Quote:
Originally Posted by Two340'sman
That is very helpful, I did take apart the digital one, also held together by a central screw, looked complicated, but I did see no series polarity protection diode.
Will have a look at the analogue one. Thanks again.
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The basic digital one uses the same case as the analogue one with a plain plated/bezel in place of the clear meter screen so the basic circuitry is likely to be the same with an ADC/voltmeter chip set up to read the voltage across the Wheatstone Bridge and hence display the CO content.
The Gastester Professional i think it was called also has battery volts, rpm, dwell(?) as well as the CO readings. Oviously a bit more involved but i suspect on the simple digital one, it probably uses generic components so replacing the 7805 and possibly the ADC and/or display driver chip will get it up and running for you. The display being LED is of course protected anyway!
On both of them, adding a 1N4007 as a serie polarity protection diode will do the job, cheap, simple add-on to prevent further accidents! The 4007 is rated at 1A but then so is the 7805 so will be up to the job of protecting it happily.