ADWSystems
Member
I have a 0-5V input ADC and need to measure voltages between 0V and almost 24V. I need to do this without altering the resolution. So a simple resistor divider is out. I was thinking of using an opamp in a differential mode, with one input hooked to a resistor divider to input different ranges (0, 4.5, 9, 13.5, and 18). Starting at the highest range, if the ADC reads 0 then move to the next lower range until the ADC returns a reading.
It looks good to me on paper. I am now working to find an available opamp to fit in the circuit. As the inputs will be 0 to 24v, I think the power supply will need to be the same. The output will only be 0 to 5v, so plenty of headroom on the high side but will need to include Vee on the low side. I might be able to get a supply with -Vee but the opamps I have seen are specified +/-15V dual supply or +36v single supply. What happens if I use -5v and +24v? Smoke?
Is there another circuit I might consider? How do I find an opamp to fit the bill? I spent an hour trying to get Digikey to help narrow down the list but without success.
It looks good to me on paper. I am now working to find an available opamp to fit in the circuit. As the inputs will be 0 to 24v, I think the power supply will need to be the same. The output will only be 0 to 5v, so plenty of headroom on the high side but will need to include Vee on the low side. I might be able to get a supply with -Vee but the opamps I have seen are specified +/-15V dual supply or +36v single supply. What happens if I use -5v and +24v? Smoke?
Is there another circuit I might consider? How do I find an opamp to fit the bill? I spent an hour trying to get Digikey to help narrow down the list but without success.