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