Designing an Ohm Meter

Jeffrey Drake · 2007-05-11T04:11:16+00:00

I am in the midst of designing an ohm meter. Due to certain designconstraints, I must use a Basic Stamp II for the first design. Laterdesigns 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 constantcurrent source. I am thinking about this one, because with a diode anda resistor it can provide a temperature independent current source,which I can supply the load resistor that is being tested. This way, Ican get a nice linear relationship that is not possible with awheatstone bridge. I have found the LM334Z to be $1.50 on (note Canadian), but would like a cheaper variety.To display the results, I have been looking at an LTC-4727JR 4 digit16 DIP 7 segment display ($2.95 @ 5 quantity) but unsure what kind ofchip I can use to drive it.I am looking into a digital potentiometer to provide an autorangingability.One of the drawbacks to the Basic Stamp II is that it has no ADC onit. I have found a project page that mentions the MAX187, but it isinsanely expensive on digikey. I have found other ADCs that are morereasonably priced, but unsure what to look for.Any suggestions?- Jeffrey Drake.