Home-made Oxygen Analysers - Unit 2

For the next analyser, I tried the analyser detailed on Keith Sabine's site (and others) where you directly hack the digital panel meter module. Yeah, it sounds dodgy but is straightforward as long as you have a suitably fine soldering iron bit.
At this stage in proceedings, I was interested in preserving the DPM for later use in a tidier version of Dave Cordes' analyser, so this sort of explains the next action.
Rather than remove the 500 ohm resistor (it's the green one 'above' the two orange ones), I decide to piggy-back a 150 ohm resistor onto the existing 500 thus giving the desired 120 ohm value. But, I didn't have a 150 ohm (or a 120) so that was made from a 100 and a 47 in series. Having done this, I'd recommend replacing the 500 ohm resistor.
So why haven't I replaced it yet? If it ain't broke, don't fix it.

mk2 - dpm hacks (closeup) small.jpg (12130 bytes)

Next we had to remove the variable pot - tried it carefully, but ended up ripping one pin off. This was replaced with a 500R 18 turn, 79p, trimmer pot (I like those pots!) from Maplin. This had the added advantage of soldering straight to the board, so no need for flying leads etc.
And that was it. Just had to mount the thing into something suitable (an old DAT tape box proved ideal). A little bit of hot melt glue for speed soon saw the unit in action.

mk2 - in use 36.9 (closeup) small.jpg (12898 bytes)

Once again, the knob-on-a-rivet was used to adjust the pot. The punched hole was suitably tight to prevent the rivet falling out.

mk2 - adjustment (closeup, good) small.jpg (14502 bytes)

Becuase I only have the one sensor, the curly lead (stereo extension lead - 1 from the 'cheap shop') is fitted with a 3.5mm jack plug at each end, enabling me to sample using either meter just by simply unplugging and replugging the lead..

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