Computing stuff tied to the physical world

Posts Tagged ‘Toolkit’

TK – Programming

In Software on Jun 21, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Time for a different subject. All the tools discussed so far have been about electronics and computing hardware.

But what about the flip side of that computing coin – software?

As mentioned recently, software has no “fixed point”. There’s no single center of its universe. Everything is split across the dimension of programming language choice. We’re operating in a computing world divided by language barriers – just like in the real world.

Here’s the language divide, as seen on GitHub (graph extracted from this Zoom.it site):

Screen Shot 2012 06 20 at 19 51 36

Here’s another one, from the TIOBE Programming Community Index:

Screen Shot 2012 06 20 at 22 28 27

(note the complete lack of correlation between these two examples)

It’s easy to get carried away by this. Is “my” language up? Or is it down? How does language X compare to Y?

Yawn.

Programming language choice (as in real life, with natural languages) has huge implications, because to get to know a language really well, you have to spend 10,000 hours working with it. Maybe 9,863 if you try really hard.

As we learn something, we get better at it. As we get better at something, we become more productive with it.

So… everyone picks one (or perhaps a few) of the above languages and goes through the same process. We learn, we evolve, and we gain new competences. And then we find out that it’s a rabbit hole: languages do not inter-operate at a very low level. One of the best ways to inter-operate with other software these days is probably something called ZeroMQ: a carefully designed low-fat interface at the network-communication level.

The analogy with real-world spoken languages is intriguing: we all eat bread, no matter what our nationality is or which language we speak (bear with me, I’m simplifying a bit). We can walk into a shop in another country, and we’ll figure out a way to obtain some bread, because the goods and the monetary exchange structure are both bound to be the very similar. Language will be a stumbling block, but not a show stopper. We won’t starve.

In the same way, you can think of information exchanges as bread. If we define appropriate data structures and clear mappings to bits and bytes, then we can get them from one system to the other via libraries such as ZeroMQ.

Which brings me to the point I’m trying to make here: programming language choice is no longer a key issue!

What matters, are the high-level data structures we come up with and the protocols (in a loosely defined manner) we use for the interactions. The bread is what it’s about (data). Money is needed to make things happen (e.g. ZeroMQ), and programming languages are going to differ and change over time anyway – so who cares.

We should stop trying to convince each other that everything needs to be written in one programming language. Humanity has had plenty of time to deal with similar natural language hurdles, and look where we stand today…

I feel reasonably qualified to make statements about languages. I speak four natural languages more or less fluently, and I’ve programmed in at least half a dozen programming languages for over two years each (some for over a decade, and with three I think may have passed that 10,000 hour mark). In both contexts, I tend to favor the less widespread languages. It’s a personal choice and it works really well for me. I get stuff done.

Then again, this weblog is written in English, and I spend quite a bit of my time and energy writing in C. That more or less says it all, really: English is the lingua franca of the (Western) internet, and C is the universal language used to implement just about everything on top with. That’s what de facto standards are about!

So what will I pick to program in for Physical Computing, embedded micros, laptops, and the web? The jury is still out on that, but chances are that it will not be any of the first 12 languages in either of those two lists above.

But no worries. We’ll still be able to talk to each other and both have fun, and the software I write will be usable regardless of your mother’s tongue – or your father’s programming language :)

Let’s focus on our software design structures, and our data exchange formats. The rest is too ephemeral.

TK – Multimeter accuracy

In Hardware on May 31, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Once you get into calibration stuff, it’s hard to stop. I recently bought this DMMCheck from voltagestandard.com:

DSC 3314

The nice thing about this unit is that it’s fully self-contained (with a 9V battery on the back) and that it has all the bits and pieces on board to check a multimeter’s (DC) voltage, (DC) current, and resistance measurements.

It comes with a calibration report – the voltage has been trimmed to exactly 5V, but the rest will have slightly different values due to component and temperature tolerances. Also, it was calibrated at 70°F (21.1°C):

DSC 3315

Here are my HP 34401A measurements, with only 15 minutes warm-up (it’s now about 23.5°C here at JeeLabs):

DSC 3316

DSC 3317

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Very close – more than close enough to start checking the VC170 multimeter I described recently, for example:

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Easily within spec. Note that a VC170 only has 400 µA + 400 mA ranges, and 1 mA only shows 2 decimal points.

Here’s a higher-spec VC940, which I find unconvincing – I use it rarely anyway, due to its slow refresh rate:

DSC 3324

Here’s a very low end Extech MN15 – it performs worse than the VC170 and can only display values up to 1999:

DSC 3328 DSC 3325 DSC 3327

And finally, as flash from the past, a cheap analog multimeter – this one is probably over 30 years old:

DSC 3329

We’ve sure come a long way, from trying to guess the value while not mixing up all those scales!

This reaffirms my choice of using the VC170 for day-to-day use, with the high-end HP 34401A used for top accuracy and for long-running experiments (handheld multimeters always auto-shutdown much too quickly).

As you can see, the DMMCheck is an superb little tool to quickly do a sanity check of your multimeter(s). There’s now also a DMMCheck Plus with extra signals to check AC voltage + current, and even frequency + duty cycle.

If you take lots of measurements over the years, it’s well worth getting something like this to verify your DMM.

This all relates to a discipline called metrology (no, not “meteo”, but “metrics”) – i.e. the science of measurement.

TK – Frequency Meter

In Hardware on May 24, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Another post about frequencies – this time I’ve assembled a DFD4A from Almost All Digital Electronics:

DSC 3124

It’s a low-cost frequency counter which goes all the way up to 3 GHz. Here it’s measuring a 10 MHz signal from my Frequency Generator, while synchronized to the Rubidium frequency standard.

As you can see, it’s spot on – the last digit flips between 0 and 1 every so often, that’s all.

As with the Capacitance Meter I assembled recently, this kit comes with detailed build instructions. Except that this time I didn’t really want to build it, so I got the pre-built version instead, including the connectors and (fully) plastic enclosure. The front plate already has all the right cutouts, and a printed piece of paper (!) glued to the front. Works ok, but I suspect that it’ll get dirty over time.

The unit came with all the parts, I just had to solder a few components and wires in place after inserting all the switches and BNC connectors.

One thing missing was the 9V battery clip – but not to worry, I have a couple of those lying around anyway.

The reason to get this particular unit was its high frequency range of well over the 868 MHz and 2.4 GHz frequencies I may want to measure here at JeeLabs. The main difference with a professional unit is probably the fact that it doesn’t have many input signal options:

  • HF measures from 0 to 30 MHz, with 5 Vpp max into a high impedance input
  • UHF measures from 10 to 3000 MHz over a 50 Ω input (max 15 dBm)

No way to directly measure the 868 MHz output from an RFM12B, I suspect – i.e. it probably won’t be sensitive enough to measure 0 dBm.

The slow measurement mode continuously collects data for one second, so you get 1 Hz resolution on the HF range and 100 Hz resolution on the UHF range (since that’s essentially just a ÷ 100 prescaler).

The fast measurement mode runs 10 times per second, i.e. a gate time of 0.1s – so this gives 10 Hz resolution on HF and 1000 Hz (1 KHz) resolution on UHF.

It’s a bit odd that the display shows more significant digits than are being measured in all but FAST + HF mode, but no big deal – the current mode is clearly visible from the switch settings.

Knowing that the counter is very accurate (for now – it’ll no doubt gradually drift slightly), it’s time to find out how accurate the TG2511 AWG’s frequency is when not synchronized to the Rubidium standard:

DSC 3125

That’s only 0.4 ppm off and well within spec – excellent!

TK – Voltage accuracy

In Hardware on May 10, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

(this is a bit of a side excursion, about checking the quality of a measuring instrument)

“Ah, but is it any good?” – that’s the inevitable question to ask when getting a precise instrument, right?

I’m referring to the 6.5 digit 34401A HP (now Agilent) multimeter I got my hands on, recently. This translates to: better than 1 ppm (part per million), i.e. 10,000 times more accurate than one percent!

This is the sort of thing the members of the volt-nuts mailing list ponder about, I would imagine.

In my case, with now over half a dozen ways to measure voltage here (numerous hand-held multimeters, mostly), I just wanted to know which one to trust most and to what extent.

The solution comes in the form of a transfer voltage standard – an item you can order, gets shipped to you, and which then gives a certain level of confidence that it will provide a fixed voltage reference. As it turns out, Geller Labs offer just such a thing at low cost – it’s called the SVR 2.0:

DSC 3078

Put 15V on its input (left), wait 30 min, and the output pins (right) will produce exactly 10.00000 Volt – magic!

Each board is “burned in” (kept turned on) for 200 hours and calibrated at the temperature you specify (I asked for 21°C). You even get the measured temperature coefficient at that spot (mine is 1.7 ppm/°C), so you can in fact predict the voltage it will generate at a slightly different temperature. Now that’s serious calibration!

My bench-top multimeter will indeed go down to 1 ppm in 6-digit mode, i.e. steps of 10 µV when measuring 10 V:

DSC 3079

And guess what – after a 30-minute warm-up (both the 34401A and the SVR), it’s spot on.

No last-digit jitter, nothing. A constant 10.000,00 readout. The current room temperature is 21.1°C, heh.

Think about it for a second: as hobbyist, you can order a precision second-hand instrument from eBay, Google around a bit to find a little voltage standard, have ‘em shipped from different parts of the planet, get them here within two weeks, hook up some wires, wait 30 minutes, and they match to 0.000,1 % precision.

Given that this instrument is from the 90′s, I’m massively impressed. This 34401A HP thing rocks!

Voltage? Current? Resistance? Game over – for me, this is more than enough precision for serious use.

TK – Equivalent Series Resistance

In Hardware on May 3, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Equivalent Series Resistance, or ESR, is the resistance of a capacitor. Huh? Let me explain…

A perfect capacitor has a specific capacitance, no resistance, and no inductance. Think of a capacitor as a set of parallel plates, close to each other, but isolated. When you apply a voltage, electrons flow in on one side and electrons flow out on the other side until the voltage (potential difference) across the plates “pushes back” enough to prevent more electrons from flowing. Then the flow stops.

It’s a bit of a twisted analogy, but that’s basically what happens. A capacitor acts like a teeny weeny battery.

But no real capacitor is perfect, of course. One of the properties of a capacitor is that it has an inner resistance, which can be modeled as a resistor in series with a perfect capacitor. Hence the term “ESR”.

Resistance messes up things. For any current that flows, it eats up some of that energy, creating a voltage potential and more importantly: generating waste heat inside the capacitor.

ESR is something you don’t want in hefty power supplies, where big electrolytic capacitors are used to smooth out the ripple voltage coming from rectified AC, as provided by a transformer for example. With large power supplies, these currents going in and out of the capacitor lead to self-heating. This warms up the electrolyte in the caps, which in turn can dramatically reduce their lifetimes. Caps tend to age over time, and will occasionally break down. So to fix old electronic devices: check the big caps first!

Measuring ESR isn’t trivial. You have to charge and discharge the cap, and watch the effects of the inner resistance. And you have to cover a fairly large capacitance range.

This ESR70 instrument from Peak Instruments does just that, and also measures the capacitance value:

DSC 3055

It’s protected against large voltages, in case the capacitor under test happens to still have a charge in it (a cap is a tiny battery, remember?). The clips are gold-plated to lower the contact resistance – and removable, nice touch!

In this example, I used a 47 µF 25V electrolytic capacitor, and it ended up being slightly less than 47 µF and having an ESR of 0.6 Ω as you can see.

It this cap were used in a 1A power supply to filter the ripple from a transformer, then its ESR could generate up to 0.6 W of heat – which would most likely destroy this little capacitor in no time.

Fortunately, big caps have a much lower ESR. It measured 0 (i.e. < 0.01 Ω) with a 6800 µF unit, for example.

As with last week’s unit, this is not an indispensable instrument. But very convenient for what it does.

TK – Semiconductor Analyzer

In Hardware on Apr 26, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Today’s episode is about a little gadget called the DCA55 Semiconductor Analyzer from Peak Electronics:

DSC 3053

It’s a nifty little self-contained unit, which identifies a range of 2- and 3-pin semiconductors, their pinouts, and some useful characteristics:

  • NPN and PNP Bipolar Junction Transistors and Darlingtons
  • Various types of MOSFETs and Junction FETs
  • Low-power thryristors and triacs
  • Diode and diode networks, as well as LEDs

The convenient bit is that you just hook up all the pins, press ON, and this gadget will figure it out, all by itself.

Here’s a BC549C transistor, i.e. a very common high-gain NPN transistor:

DSC 3051

And here’s an example from the datasheet, showing all the info you get:

Screen Shot 2012 04 17 at 18 10 49

I wouldn’t call this unit indispensable – most of this can also be derived with a battery, a few resistors, and a multimeter – but it’s darn convenient, if you regularly re-use stuff from your spare parts bin, as I often do.

TK – Resolution vs accuracy

In Hardware on Apr 19, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

This episode is not about an instrument you will normally need, but about using a high-end unit.

Once you get into measuring instruments, there’s a trap – the kick of going after models which have more and more resolution and accuracy. First, let me explain the difference – i.e. roughly speaking:

  • resolution is the number of digits you can measure
  • accuracy is how close that value is to the real value

So you could have a 3-digit multimeter which is spot-on, and in most scenarios it’d probably be much more useful than a 5-digit multimeter which delivers meaningless results because it’s not properly calibrated.

The trouble with this search for perfection is that it can be addictive – see the time-nuts site for one example of keeping track of the EXACT time. Over the top for most mortals, but hey, I can relate to this sort of craziness :)

And recently I fell into the same trap. I’ve got quite a few hand-held multimeters, but when someone pointed out some eBay offers of a 6.5 digit HP/Agilent bench-top multimeter, I simply couldn’t resist and bought one:

DSC 3050

An amazing instrument – above it’s measuring between 1.8 and 2.0 µV with the probes shorted out. It’s a second-hand unit, probably from the 90′s, so it’ll be out of calibration by now. I could send it to a calibration lab, where they tweak the thing until it’s back to its sub-ppm accuracy, but that might well cost as much as what I paid for it. So for now I’ll just assume its accuracy is decent, perhaps in the 5-digit range. More than good enough for the experiments at JeeLabs anyway. This is all for fun, after all.

One of the interesting specs of this multimeter is a selectable input resistance of over 10,000 MΩ on DC ranges up to 10V. This extremely high value is great for measuring the leakage of a capacitor. Let’s try it:

  • first, a 47 µF 25V cap is charged to slightly over 5V for a few minutes
  • then, the power supply is disconnected and it starts discharging
  • finally, we measure the time it takes to discharge from 5V to 3.16V
  • this was determined to be well over six hours (I stopped waiting!)

I picked this voltage range because 3.16V is 63.2% of 5V, so the measured time corresponds to the time constant of the T = R x C formula for capacitor discharge. In other words:

  • 20000 s = R x 47 µF
  • therefore, the internal leakage resistance R = 20000 / 47 ≈ 425 MΩ
  • this translates to an internal leakage current of under 5 V / 425 MΩ ≈ 12 nA

So without even having an instrument which can measure such extremely low currents, we can arrive at an estimate of the leakage of this particular 47 µF 25V electrolytic capacitor, and under 12 nA is not bad!

Update – see the comments below, the leakage is even lower because the discharge should be measured to 1.84V iso 3.16V – so it’s well under 10 nA for this capacitor, in fact!

TK – Resistors

In Hardware on Apr 12, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Yet another useful package from Conrad (NL #418714) – a set of 390 resistors from 10 Ω through 1 MΩ:

DSC 3048

Resistors come in specific values and are based on a logarithmic range, i.e. you’ll see them organized as “E6″, “E12″, or “E24″, meaning that they are split up into 6, 12, or 24 values per decade, respectively.

Here’s some info about what’s in that above box:

Screen Shot 2012 03 29 at 13 11 35

This is actually mostly a subset of the E6 range (which is 10, 15, 22, 33, 47, 68) – see this Wikipedia article about preferred numbers for how and why things are organized that way.

The point is that you can never have enough resistors, which can probably be considered to be the most elementary components in electronics. Whether for limiting the current through a LED or creating a voltage divider, these things just tend to get used all over the place.

But what if you need a different value? Well, that’s often trivial: by using two resistors, either in series or in parallel, it’s often possible to get real close to the value you’re after.

The formula for two resistors in series is simply the sum of their values:

    Rseries = R1 + R2

The formula for two resistors in parallel is slightly more complicated:

    Rparallel = (R1 x R2) / (R1 + R2)

(this can easily be explained using Ohm’s law, I’ll be happy to write a post about this if you’re interested)

Here’s an online calculator which will find the proper values – although I recommend doing the math yourself, at least initially, because it will help you get a good grasp of how resistors work together.

TK – Burden voltage

In Hardware on Apr 5, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Two weeks ago, I extolled the virtues of the multimeter for measuring various electrical units.

With voltages, things are very simple: you’ve got two probes, and you can stick them anywhere in your circuit to measure the voltage potential difference between two points. The input impedance of any modern multimeter is usually 10 MΩ or more, which means the load caused by measuring is neglegible in just about all cases.

Let’s apply Ohm’s law: 10 MΩ over 1V is just 0.1 µA current, and over 230V it’s still just 23 µA current.

But with current measurements, things change: a multimeter in current measurement mode is essentially a short. You place the probe pins between the supplier and consumer of current to measure the Amps, milliamps, or microamps. That also means you can’t just go probing around at random: sticking the probes between + and – of a power supply, or even just a battery, basically creates a short. The result is a huge current, which will blow the internal fuse of the multimeter. Very often, the fuse is a 500 mA type (to protect a 400 mA range).

That’s why the VC170 (left) is better than the VC160 (right) – voltage and current are on different jacks:

DSC 2979

But there’s another aspect of current measurement with multimeters to be aware of: burden voltage.

When measuring current, multimeters insert a small resistance in series with the load, i.e. between the two probe pins, and then work by measuring the voltage drop across them (Ohm’s law, again!).

So placing multimeter between current supplier and consumer actually introduces a small voltage drop. How much? Well, that depends both on the multimeter and on the selected range.

Here’s the VC170 with a 1 mA current through it – in its 400 mA range:

DSC 2977

I used the VC160 multimeter to measure the voltage over the VC170 multimeter, which is in current measurement mode. This is one example why having several multimeters can come in handy at times.

Not bad – roughly 1 mV to measure 1 mA, so the burden resistor in this unit for the 400 mA range is somewhere around 1.3 Ω. Note also that with 400 mA, the voltage drop will rise to over 500 mV!

Let’s repeat this with the VC170 in µA range, i.e. measuring up to 4000 µA:

DSC 2978

Hmmm… the voltage drop with 1 mA is now 100 mV, i.e a 100 Ω burden resistor. Not stellar.

Why is this a problem? Let’s take an example from the JeeNode world: say you want to measure the current consumed by the JeeNode once it has started up and entered some sort of low-power state in your sketch. You expect to see a few µA, so you place the multimeter in µA mode.

The JeeNode starts up, powered from say a 3.6V 3x AA battery pack with EneLoops. It starts up in full power mode, briefly drawing perhaps 10 mA. You’ve got the multimeter in series, which in µA mode means that you’ve got a 100 Ω resistor in series with the battery.

The problem: at 10 mA, a 100 Ω resistor will cause a 1V drop (BTW, make sure you can dream these cases of Ohm’s law, it’s an extremely useful skill). That comes out as 100 V/A burden voltage.

So the battery gives out 3.6V, but only 2.6V reaches the JeeNode. Supposing its ATmega is set to the default fuse settings, then the brown-out detector will force a reset at 2.7V – whoops! You’re about to witness a JeeNode constantly getting reset – just by measuring its current consumption!

In the 400 mA range, the voltage drop at 10 mA will be 13 mV and affect the circuit less (1.3 V/A burden voltage).

The good news is that the multimeter still does auto-ranging. As you can see in the above example, 1 mA is shown with 2 significant decimals, so it’s still possible to read out ± 10 µA in this mode (don’t assume it’ll be accurate beyond perhaps ± 30 µA, though).

Can this problem be avoided? Sure. Several ways:

  • stick to the higher current ranges, even if that means you can’t see low values very precisely
  • add a Schottky diode in forward mode over the multimeter – this will limit the voltage drop to about 0.3V, even during that brief 10 mA startup peak
  • get a better instrument – this is easier said than done, most multimeters have a 1..100 V/A burden voltage (!)
  • look at Dave Jones’ µCurrent adapter, which converts low currents to a decent ± 1V range with only 0.07 V/A burden voltage

One caveat with Dave’s solution is that it is never in stock. I’ve been trying to get one for years without luck. He occasionally gets new ones made, but they tend to sell out within nanoseconds, AFAICT!

TK – Basic tools

In Hardware on Mar 29, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Today just some more general notes about stuff which you probably already have: screwdrivers, pliers, tweezers, that sort of stuff. None of this is electronic – but some details do tend to matter in this context.

The toolkit I picked for this series is item 814892 from Conrad, or rather 046027, which is the multimeter plus this set, as a package deal:

814892 BB 02 FB EPS

Don’t expect top-of-the-line professional tools – just stuff which ought to work nicely. The idea is that if any of those tools break, then apparently you’re using it a lot, so maybe now’s a good time to get a better-quality version of that particular tool! – and the rest still comes in handy. By then, you’ll already have some experience, and you’ll be better equipped to pick a good brand which meets your need. It may sound crazy, but by the time you’ve managed to break all of these tools, you’ll have gained plenty of experience with each of them (or you’re handling them too roughly). Either way, it’s still worth the initial expense!

One of the tools you’ll use a lot are side-cutters, to snip off the wires of resistors, caps, etc. after having soldered these components into your circuit or onto your board. The one in this set works, but also illustrates the kind-of-average build quality of these items:

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The jaws will cut just fine, but they are not 100% parallel – it’ll cut better near the end (which is what matters most anyway), than inside where these cutters don’t fully close. But hey – they do work.

Other items in this toolbox are: various types of screwdrivers (flat, philips, and torque), hex spanners, and such. Nothing spectacular, but they come in small sizes – very convenient for electronics use.

There’s a little magnetic LED light (yawn), a loupe (oh so handy, at times, with SMD), and some less common utilities like a magnet on a telescopic pointer and a long “gripper” – useful to get screws accidentally dropped in some hard-to-reach spots, I suppose.

Furthermore there are two types of tweezers in this collection, a straight “reverse-action” type which opens when squeezed, and one bent to the side. Both can be extremely useful, for very different purposes: the straight one acts like a weak clip, since it springs back closed when released. It can be used to gently hold something in place while you’re soldering or measuring it (it does conduct heat, so don’t put it too close to the spot you want to solder).

The standard tweezer is an excellent example of a prolongement du corps – an extension of your body, letting you do more than you’d think possible. I prefer this “angled” type with a bend in it over straight models. It takes very little time to learn to pick up and manipulate tiny SMD components with it. I remember quite well how amazed I was when trying this for the first time with sub-millimeter SMDs – felt a bit like being a neuro-surgeon :)

None of these items are very special. You probably have most of them already. Otherwise, just be sure to get at least the side-cutters, the standard tweezers, and a loupe (or small magnifying glass) … even if you don’t do SMD.

TK – Multimeter

In Hardware on Mar 22, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

One of the tools you don’t strictly need, but which I very strongly recommend getting, is a multimeter.

A multimeter measures stuff. I picked the Voltcraft VC170, Conrad’s own (re-)brand (item 124403):

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Actually, my suggestion for this series would be to get item 046027, which includes a whole set of additional tools for only €12 extra. It won’t break the bank, and it gets you various screwdrivers, tweezers, a simple loupe, a lamp, and a few more items.

Anyway, back to the multimeter. Trust me – this is one of those lab instruments which will enable you to learn more about electricity than anything else. And this is one of those cases where a small amount of money will go a huge way – this particular unit lets you measure voltage, current, resistance, frequency, and more. The VC170 even does non-contact AC mains sensing, to detect live wires from a short distance.

I’ve got over half a dozen multimeters by now. Low-cost as well as expensive / more accurate ones. My favorite one is this VC170 (or rather, its predecessor, the VC160 which I’ve been using for several years now). Why? Because it’s very small, it’s fast and responsive, and it offers an excellent set of trade-offs.

Some more expensive ones are very sluggish (but also produce considerably more accurate 5-digit readings), some beep very annoyingly all the time, and some don’t have the sensitivity you need. Of all the multimeters I have, I end up using my trusty VC160 most of the time. It does what I need, and it doesn’t fill up my desk.

You can’t really go wrong with this. You’ll want more than one multimeter if you really get into electronics. Here’s a not-too-contrived example: measuring incoming and outgoing voltages of a power regulator at the same time, as well as incoming and outgoing currents – that’s 4 multimeters! So by the time you want a more advanced one, this first unit will still come in handy in certain use cases.

The good news is that one is fine for a huge range of situations. This one will measure up to 230 VAC mains (with a small caveat, see below), and all the way down to fractions of a µA of current (ultra-low power, anyone?).

Learning how to make the most of a multimeter is a story far beyond this initial Thursday Toolkit series. But it’s really easy to get started and learn along the way. Even just fiddling with a resistor, or a capacitor and a resistor, and measuring what happens in various hookups can be a great way to understand Ohm’s law, and all the basics of electronic circuits. Do two resistors in series draw more or less current? What is the resistance of two resistors in parallel? How much voltage are my near-dead batteries giving out, and how are they performing under load? Is that power supply doing what it’s supposed to do? And perhaps most important of all: are the proper voltages being applied to the different parts of my circuit? Trivial stuff with a multimeter – you can simply measure it!

Multimeters are very robust, especially auto-ranging ones like this, which can take any voltage and figure out all by themselves whether it’s over 100 V or in the millivolt range. But there are ways to break things. Big currents always tend to cause trouble, and even the best multimeter won’t be pleased if you push a few amps through it while it’s trying to measure microamps. Which is why the above set of input jacks is actually quite nice: voltage and current are very different quantities, and you have to hook up the measuring cables in specific ways to measure the different types of units. But mess-ups do happen… I’ve blown fuses inside my multimeters a few times – fortunately, they are easy to replace.

All multimeters have trade-offs. This one gets many of them right though, and does auto-ranging.

Then again, this multimeter seems to be at its limit when asked to measure 230 VAC, i.e. AC mains around here. It displays “OL” (overload). But it can measure 230 VAC just fine when using the “Select” button to fix it to the maximum range before doing the measurement.

The other thing is not to get carried away by the 4-digit display. You’ll be able to measure 3999 vs 4000, but that’s not an absolute accuracy, i.e. you shouldn’t expect to be spot on when measuring 3.999 V versus 4.000 V – the accuracy is only about 1.5 %, so it might well be 3.940 V, or 4.060 V. The only purpose this serves, is to show you slight fluctuations – fairly accurately. So it might be off a bit, but you will be able to see small dips and increases in voltage, current, resistance, etc.

And to be honest: 1.5 % accuracy is actually pretty amazing for such a low-cost instrument, if you compare it to the old analog multimeters which you had to read out by estimating the position of their needle!

The VC170 added a function I’ve dearly missed on the VC160: frequency measurements. Its specs says that it works up to 10 MHz, but a quick test here tells me that it’ll work up to at least 25 MHz with a 1 Vpp signal (wait for tomorrow’s post to find out how I tested that). The frequency range is in fact very convenient for microcontroller debugging of timing loops, for example – I’ll go into this in a future post.

So much for the multimeter. If you solder electronic circuits together, all I can say is: get one!

TK – Soldering Iron

In Hardware on Mar 15, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

The very first tool you’ll need – inevitably – when going beyond breadboards and wire jumpers to hook stuff together, i.e. when building things which need to become more or less permanent, is a soldering iron.

A soldering iron is just a heater which gets hot enough to melt solder. For the solder used in electronics, the iron’s tip is usually kept at between 275°C and 375°C. That’s more than hot enough to give you a serious burn when touched. So the whole idea of a soldering iron is really to get that heat in the right place, while giving you a way to hold the thing and manipulate it fairly precisely.

There are tons of different models, costing from €10 to €1000. The idea here is to pick one which doesn’t burn a hole in your pocket (heh, turned off, I mean :) – The target I’ve set myself for this initial Thursday Toolkit series is to be able to get all the tools you need for having oodles of fun with various Physical Computing projects for a total of under €150.

That rules out a lot of soldering irons, and forces use to focus on two essential features, i.e. that the soldering iron has enough heat to work well, and also has some sort of basic temperature control. A soldering iron which is too cold will be an awful time-consuming hassle, but one which is too hot will burn and damage electrical components, and will oxidize the solder much too quickly. The big fat uncontrolled “after-burners” used by electricians and plumbers are not suitable here.

As mentioned in the initial post, I decided to buy all the tools at Conrad, item 588417 in this case:

DSC 2940

(just the iron and the two tubes at the left are included – the rest was ordered separately)

What I like about this 45W unit is that it has a solid base and sort of a temperature control, letting you regulate how much heat gets generated. This is definitely a low-end unit. Another option, with a better (smaller!) soldering iron, is the Aoyue 936 (here’s a link to a Dutch shop carrying this particular model).

The Conrad unit is a soldering iron heated at 230 VAC. Let’s have a look in close up:

DSC 2942

It’s all about heat, and keeping it away from your hand. You hold it like a big pencil or marker, and after an hour or so of use, you’ll note that the middle of that thing gets warm, but not too hot – which is the whole idea. The metal part is the hot end, as you’ll quickly find out once you touch it and get a nasty burn. Trust me, you will get burned at least once – it comes with the hobby…

As I said, this is a low-end unit. One of the compromises is that the hot end is fairly large – so holding this thing steady and accurately placing the tip where you want it takes some practice. But no worries – everyone starts out this way, and many of us keep on working with such a unit for years. It works fine.

The other compromise is that this unit isn’t really controlled by a thermostat, it’s really just trying to keep the tip at a somewhat constant temperature, based on thermal flow in free air. Let’s take it apart:

DSC 2945

The shiny metal barrel is the heater. Some nichrome wire, wound inside an isolated jacket no doubt. Much like toasters, hair driers, etc – but only 45W. In the middle sits a big metal core, with the pointy tip we’ll be soldering with. Its main task is to conduct the heat to the tip, and being such a large piece of metal, it’ll keep a reasonably constant temperature, even when the tip touches the copper and wires of the circuit being soldered.

There are two heat-insulated wires to the heater, powered from AC mains. The third wire is ground, and is attached directly to the barrel. This provides three types of safety: 1) if the heater breaks down, it’ll cause a short to ground and blow your AC mains fuse instead of electrocuting you, 2) if you accidentally burn through a wire carrying AC mains current (such as the soldering iron’s own!) it’ll also blow a fuse, and 3) the tip of the soldering iron is at ground potential, so any static electricity around your circuit will be conducted safely away from the sensitive electronic parts.

Then there’s the base, where the hot soldering iron is kept between your soldering work. Note the metal spring / holder, which keeps soldering iron itself hot, but tries to stay reasonably cool to the the touch on the outside. You’re not going to get burned touching it – just a quick reminder that there’s something very hot inside!

And then there’s this thing:

DSC 2943

That’s actually a synthetic sponge. It’ll probably make more sense once you soak it in water:

DSC 2944

Part of the skill needed to solder stuff together, is to keep a good clean soldering tip. Solder tends to oxidize, so over time you’ll get in the habit if wiping that scorching hot tip clean and applying fresh solder. The wet sponge is one way to clean that tip – it’ll sizzle and scorch a bit, but it works fine.

So much for the venerable soldering iron. Get one, don’t go overboard on features (a small size is great, but it’ll cost ya’). Far more important is to get a decent one and practice, practice, practice! – I won’t go into the actual soldering skills here, there are plenty of articles, books, and weblogs on internet, so my suggestion would be to just google around a bit. And then: practice – there’s no magic pill around that.

Next week, I’ll go into one of the best other investments you can make – apart from the soldering iron.

Thursday Toolkit

In Hardware on Mar 8, 2012 at 00:01

Welcome to a second new initiative on this weblog: a weekly series about tools, i.e. the stuff you can use to design and create stuff, in the context of Physical Computing, that is. Again, you can bookmark this Toolkit link to find back all the related posts on this weblog, now and later.

People regularly ask about what to get, how to get started, and sometimes I see comments indicating that maybe a few basic extra investments might help understand and fix a problem much quicker.

Tools can be anything: the soldering iron you use, various electronics “lab instruments”, but also the software you use, and even the computer setup you work with. There is no “best” answer. It’s all matter of goals, interest levels, amount of involvement, and of course budget.

What I’d like to do is start off this series from scratch. I vividly remember the time when I re-booted my interest in electronics a few years ago and started JeeLabs to get into Physical Computing. It was very confusing. Do I get the best tools money can buy? Sure, dream on, but if going broke is not an option, what do I get first? When should I buy specific items? Which items are risk-free? Is really everything required? What’s “everything”, anyway? What would be the absolute minimum? Is this the start of never-ending upgrades?

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The good news is: you can start having immense fun, and learn, and build stuff for less than the price of an Xbox. To draw on a theme from Alice in Wonderland: you can pick the red pill or the blue pill, it’s all up to you. The red pill is: watch videos, play games, surf and consume, follow the pack, compare yourself (and keep up) with others. The blue pill is: launch yourself into a new adventure, find out what so many explorative minds before you have invented, discover the gift of boundless learning, and start contributing to change the path of the future – your own, of your friends, of your community, or maybe even of your whole world. It’s all possible, these journeys are totally real (and indeed also non-virtual). Today. Now!

The even better news is, that these make incredibly nice gifts (note that gifts are not tied to a particular time of year – the best time to give IMO, is when you feel like it and can turn it into a genuine act of generosity).

Thinking about how to start off this series (which, incidentally, will be open for guest writers, so feel free to suggest topics or contribute with posts), I decided to take on the role of someone who really wants to dive into Physical Computing and has to start from scratch: knowing nothing, having nothing, eager to learn, willing to buy what’s needed – or indeed, having received some sort of starter set as a gift.

I came up with a list of items: some tools, and a fun kit to build, which can catapult you into this world of technical invention and creation. It’s meant as a suggestion – no more. Whatever works for you, ok?

Next question was – how to make this meaningful, i.e. how can people get hold of this stuff, if they simply want to get started? I decided to select appropriate items from Conrad, a mail-order shop with outlets all over Europe, which has been in the business of supplying all sorts of electronics and hobby products for many decades. You’ll find cheaper stuff in China, and you may be served better by a local company you already know, but if you really start from scratch, Conrad is a fine mail-order source of hobby-oriented products for the Europe region. And although I don’t know them as well, I suspect that Jameco has a similar audience in the US.

I do not have even the slightest affiliation with Conrad – I just order from them once in a while (and know from experience that returns and cancellations are handled in a courteous and responsive manner). Their website is not the fastest or the most convenient, but hey, it works.

Here is a list of what I found and will be discussing in the upcoming installments. Unfortunately, it appears that these item numbers are not identical across different countries – these links are to Conrad’s Dutch site:

  • indispensable: a soldering iron + some extras (item 588417)
  • just about indispensable: multi-meter + screw drivers, pliers, etc (item 046027)
  • essential, because we only have two: a third hand (item 588124)
  • consumables, better never run out of this: leaded solder (item 812803)
  • nice to “undo” soldering mistakes: desoldering wick (item 588243)
  • convenient and cheap: solder cleaner (item 588371)

Cost so far: € 86.04, including VAT and free shipping (Dutch prices, other countries should be similar).

That leaves plenty of spare cash in our sub-Xbox budget to buy one more thing: a delightful robotic kit (item 191451) – the same as used for the TwitLEDs project. Total expenses: € 146.03 (over 40% of which is that robot).

588417 GB 00 FB EPS 046027 BB 00 FB EPS 191164 LB 00 FB EPS

The coming weekly posts are going to describe these items in detail, and explain why less is too little and more is not essential. Feel free to pick alternatives, but don’t omit too many of these items. Even that robot (or some starter project) is essential. Walk first, then run. But as you’ll see, even walking is fun!

My reasoning for this approach is as follows: when starting out, you need enough to get going, to be able to really learn and get used to everything, and to build up the skills which will allow you to step up to more advanced tools – but only then, and only if you decide that you want to take it further!

Nobody in their right mind would start learning to play the violin on a Stardivarius. Well.. I have to admit that my well-documented recent oscilloscope acquisition sure feels like a “Strad”. And I’m glad I didn’t get it any sooner, or skipped the Rigol trial, because I would probably have had no idea how to make use of it otherwise.

So this series will be about picking tools, making the very most of them, and focusing on the world beyond.

It’s not the tools that matter. It’s what they enable. And it’s for everyone who’s interested, from age 7 to 77.

Update – ALthough this will slightly exceed the total budget, I recommend also getting a large set of resistors, such as Conrad’s 418714. I’ll go into this in one of the upcoming Toolkit posts.