Computing stuff tied to the physical world

Pressure cooker

In Musings on Mar 31, 2012 at 00:01

These past 36 hours have been absolutely fabulous, and exhausting…

First there was the 7th HackersNL meeting in Utrecht. The name of the event is unfortunate, IMO (this whole “hacker” monicker doesn’t sit well with normal people, i.e. 99.9% of humanity), but the presentations were both absolutely fantastic. A wide scale of design topics by David Menting, including his “linear clock” for which he designed custom hardware based on a standard tiny Linux + WiFi board, and then a talk about turning a cheap laser cutter into a pretty amazing unit by ripping out the driver board and software, and replacing it with their own custom hardware with an MBED module plus software (wiki) – by Jaap Vermaas and Peter Brier. Both cutting edge, if you pardon the pun, and above all a pressure cooker where two dozen people get to talk about “stuff”, mostly related to Physical Computing really. Everything is open source.

If you live in the neighborhood of Utrecht, I can highly recommend this recurring meeting, scheduled for the last Thursday of each month – so take note, hope to see you there, one day!

The other event was the Air Quality Egg Workshop, by Joe Saavedra. Basic idea: a sensor unit, to measure air quality in some way, plus an “egg” base station which can tie into Pachube (both ways), relays the sensor data, and includes an RGB color light plus push-button.

Except that it doesn’t exist yet. We built a wired prototype based on a Nanode with SparkFun protoshield, a CO sensor, an NO2 sensor, and a DHT22 temperature/humidity sensor.

Here’s my concoction (three of the sensors were mounted away from the heat generated by the Nanode):

DSC 3002

It’s now sitting next to the JeeLabs server, feeding Pachube periodically. We’ll see how it goes, since apparently these sensors need 24..48 hours to stabilize. Here are some of the readings so far:






What I took away from this, is:

  1. Whee, there sure is a lot more fun stuff waiting to be explored!
  2. When you put a fantastic bunch of creative people together, you get magic!
  3. Not enough time! Would it help to keep flying westwards to cram more hours into a day?
  1. I’m curious about the gas sensors, what the principle of operation is. Is there some internal heater that cycles on and off, and some sorption / desorption cycle that generates a resistance change? What kind of sensitivity do they have, and could you test it?

    • All the sensors are based on the same heater principle, and indeed one actually cycles, see for several types. One issue is the calibration part, since no-one usually has access to a controlled ppm environment of these gases.

      I’d love to find a way to get decent ppm results out, even if approximate. Also thinking about hooking these things up to an Analog Plug, so their fluctuations can be read more accurately even when the range is not full-scale on the ADC.

  2. ‘3. When you put a fantastic bunch of creative people together, you get magic!’

    I agree! Have you considered any Jeelabs centered workshops? I would be very interested in joining…maybe to workshop out some Jeemon/Jeerev stuff, etc, etc.

  3. It was fun! I’d like to suggest to solve the ‘name issue’ with a brainstorm. The regular participants of the HackersNL meetings could have a discussion about this and see if we can come up with something better. BUT I’d like to keep ‘HackersNL’ or whatever the name may be to also be connected with the Hackerspaces community, even though we’re not a space in the physical sense of the word :) Anyways, fun times and looking forward to see whatever we all can come with.

  4. So what is the best way to optimise battery use when using these sensors with heaters in, and still get reasonably stable results out ?

    • Can’t be done, I’m afraid. These units require some 125 mA continuous, and need to stabilize for 24..48 hours. Such a unit simply can’t be run off batteries – a small-sized solar panel might work for outdoor use – either way, it’s a few hundred mA continuous drain depending on how many sensors you use.

  5. Hi jcw! Can you post the schematics and the code used for Pressure cooker? I want to build one for myself and I’m not so good at electronics .. I like more the programming part. Thank you.

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