bigal_scorpio
Active Member
Hi to all,
I just realised that the PIC datasheets say that a negative voltage cannot be measured and unfortunately thats what I need to do!
I have seen one answer that uses an op-amp to invert the voltagebefore the PIC but I can't seem to do it in practice. The circuit I saw didn't mention a particular op-amp so I just looked at the specs of the ones I have and chose one that said it would work on 3 to 5v supply.
I set up the circuit on breadboard and it did seem to invert the voltage but not on a volt for volt basis When the negative voltage is varied from 0 to -5v all I see on the output is about + 4.26 v which seemed to hold steady at that and not mirror the variation in negative volts at all.
I am not at all sure about op-amps so if anyone can point me at a simple circuit or tell me that a particular one is good for my needs I would be grateful.
Thanks Al
I just realised that the PIC datasheets say that a negative voltage cannot be measured and unfortunately thats what I need to do!
I have seen one answer that uses an op-amp to invert the voltagebefore the PIC but I can't seem to do it in practice. The circuit I saw didn't mention a particular op-amp so I just looked at the specs of the ones I have and chose one that said it would work on 3 to 5v supply.
I set up the circuit on breadboard and it did seem to invert the voltage but not on a volt for volt basis When the negative voltage is varied from 0 to -5v all I see on the output is about + 4.26 v which seemed to hold steady at that and not mirror the variation in negative volts at all.
I am not at all sure about op-amps so if anyone can point me at a simple circuit or tell me that a particular one is good for my needs I would be grateful.
Thanks Al