I am in the midst of designing an ohm meter. Due to certain design constraints, I must use a Basic Stamp II for the first design. Later designs will likely replace it with a real microcontroller.
I have been considering components to satisfy my needs.
I have been considering using an LM334Z (TO-92) to supply a constant current source. I am thinking about this one, because with a diode and a resistor it can provide a temperature independent current source, which I can supply the load resistor that is being tested. This way, I can get a nice linear relationship that is not possible with a wheatstone bridge. I have found the LM334Z to be $1.50 on digikey.ca (note Canadian), but would like a cheaper variety.
To display the results, I have been looking at an LTC-4727JR 4 digit
16 DIP 7 segment display ($2.95 @ 5 quantity) but unsure what kind of chip I can use to drive it.I am looking into a digital potentiometer to provide an autoranging ability.
One of the drawbacks to the Basic Stamp II is that it has no ADC on it. I have found a project page that mentions the MAX187, but it is insanely expensive on digikey. I have found other ADCs that are more reasonably priced, but unsure what to look for.
Any suggestions?
- Jeffrey Drake.