Computing stuff tied to the physical world

Analog, but not quite

In Hardware on Nov 11, 2009 at 00:01

The original Analog Plug is a bit overkill and a bit expensive for 8 simple 12-bit channels. I’m going to switch to an MCP3424, which has “only” 4 channels. The interesting bit is that they go all the way up to 18-bit resolution – if you need only about 4 samples per second (think thermostats, voltmeters, etc).

Here’s the board I had made:


And here’s the patch I had to apply (VSS and VDD mixed up, doh!):


This sketch puts the chip in continuous 18-bit mode and reports the readings:

Screen shot 2009-11-05 at 17.54.24.png

Sample output:

Screen shot 2009-11-05 at 17.54.05.png

I tied channel 1 “-” to ground and connected a small trimpot to “+” – note that the input range is bipolar and should be within -2.5 .. +2.5 V (or less, since input gain is adjustable from 1x to 8x). The sample output shows readings while turning the trimpot a bit, with 18-bits these readings lie between -131,071 and +131,071.

Luckily only a few of these plugs have been made so far (as part of a larger panel with other stuff on it), so there’s no harm done. To redo them properly will just take a few more weeks, as usual…