Computing stuff tied to the physical world

Analog Plug

In AVR, Hardware, Software on Sep 30, 2009 at 00:01

The second plug panel has arrived. I’ll document my test results in the coming days.

First, the Analog Plug – an 8-channel 12-bit ADC connected via I2C:

DSC_0545.jpg

It’s based on the ADS7828 chip. Here’s a demo sketch to read it out:

Picture 3.png

I hooked it up using various gimmicks lying around here – this ties a trim pot to channel 4, with range 0 .. 3.3V on the wiper:

DSC_0544.jpg

As you can see, the Breadboard Connector can be used to hook up to 8 of the 12 pins of this plug.

Here’s some sample output:

Picture 1.png

I slowly turned the wiper as you can see. It stops at 4095 counts, which represents the 2.5V of its internal reference. Appears to work fine in this test setup at the maximum I2C rate, somewhere over 1 MHz. The readings didn’t change by more than one count when touching various parts of the circuit, so as first impression it looks like it’s pretty stable.

This plug has two solder jumpers, to configure its I2C address to 0×48 .. 0x4B, which in hindsight is a bit overkill. Only minor nit is that I mis-labeled the A0 jumper – as shown in the picture, the address ends up being 0×49 i.s.o. 0×48. Oh well, a small silkscreen fix will resolve that later.

So there you have it – eight 3.5 digit voltmeters on one tiny blue-and-gold plug :)

  1. Nice ! :-)

    And when are you going to offer it through the shop ?

    I also experimented this weekend with the MSP23016 ( no not the 23017) and it works great. 16 more Digital I/O’s on a square inch.

    • I don’t know. I sure hope I’m not painting myself into a corner – here’s my dilemma: I love to make these things and tinker with them. I also want to make all of this available at a reasonable cost and see all the delightful stuff fellow-tinkerers will come up with. But I don’t want to drown in complex inventory tracking or handling/shipping of individual components. I’ve only got one pair of eyes and one pair of hands… :)

      Also need to think about pre-assembled vs. kits vs. bare boards, given that most plugs are based on (a few) SMD components. By now, I find it quite easy to solder them on by hand, but not everyone will want to get into that.

      I’m inclined to batch plugs up a bit to simplify things (for me!). Perhaps make this available as pre-assembled units for now with say 1 extender plug + 1 analog (ADC) + 1 voltage (DAC). Or perhaps application specific, e.g. all the plugs needed to set up a reflow controller: blink plug + thermo plug + lcd plug.

      Could also provide bare pcb’s of any plug type, but in sets of 5 or so. The catch is that there’s probably no way to please everyone…

      This clearly needs to be resolved soon.

  2. Just found the MCP3424 chip, which is even more intriguing: 4 differential channels for -2.5V .. +2.5V, converting 12-bit @ 240 samples/sec up to 18-bit (!) @ 3.75 samples/sec.

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