No, I haven’t abandoned the Micro Power Snitch!

But some projects are trickier than others, and this one didn’t want to play along when I tried it again on my new PCB design. I fixed one glaring wiring mistake so far, but there’s more going on. Since Mr. Murphy seems to be enjoying himself again, I’m going to let him enjoy his little “victory” for a while and come back to the MPS at a (slightly) later date.

Instead, let’s move up the ladder a little and experiment with another ARM µC:

On the right: four times as much memory (both flash and RAM) and twice as many pins.

• Meet the LPC812 – Wed
• It runs the same firmware – Thu
• Soldering a TSSOP chip by hand – Fri
• Adding an RFM69 radio – Sat

As you can see, packaging is everything – and bigger is not always more…

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In this concluding part (for now) about the Micro Power Snitch, which feeds off the magnetic field around an AC mains power cable when in use, I’ll look into how the whole circuit behaves when it comes to actually sending out wireless radio packets.

The daily articles in this week’s final MPS episode are:

• CT’s and burden resistors – Wed
• Inductive spikes and safety – Thu

Update – With apologies (again!), I’m going to postpone the following posts:

• Sending out MPS packets – Fri
• Construction and final notes – Sat

It’s a huge challenge to manage the incoming energy so that everything keeps going!

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At the end of the day, the Micro Power Snitch (MPS) is really about powering up and down robustly under all circumstances. There will be times when there is no energy coming from the Current Transformer, and there will be times when energy levels hover around the go/no-go point of the circuit. That’s the hard part: being (very) decisive at all times!

This week’s episode looks at an improved circuit with a dozen individual components or so. As you will see, it has excellent snap-action behaviour, and does the right thing on the “up” ramp as well as on the “down” ramp, regardless of how slowly those voltage levels change.

Here is the daily sequence for this week:

• A revised, complete MPS – Wed
• Extremely slow ramps – Thu
• Next MPS challenge: the radio – Fri
• The MPS as prototype PCB – Sat

With a complete MPS circuit design worked out, we’re finally getting somewhere.

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There’s trouble ahead for the MPS: it’s not reliable enough yet, and can enter a “zombie mode” whereby the µC won’t have enough voltage to start up, while drawing so much current (relatively speaking) that the energy source isn’t able to raise the voltage further.

Leading to some beautiful pictures, but nevertheless totally undesired behaviour:

The daily articles in this week’s episode are:

• Pretty picture, ugly effect – Wed
• An improved MPS circuit – Thu
• It’s all about the startup “hump” – Fri
• Investigating the voltage doubler – Sat

So far, it looks like this second MPS design solves the problems of the first. Progress!

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