Stamp PLC - Analog Input Max Voltage?

BCGary

Hi;

I am building a pool/spa automation system using a Stamp PLC.· My system voltage is 24 VDC for all of the DI/DO control.· I would also like to use 24 VDC for the analog input loops (4-20 mA) but I see that the MAX1270 ADC has a maximum voltage threshold of 15.6 VDC.· The answer seems obvious that I need to use 15 VDC or less to power the analog inputs or am I missing something?· If this is the case, does anyone have an example schematic to step down my 24 VDC to 12 or 15 VDC for this purpose?

Thanks for the help.

BCGary

Phil Pilgrim (PhiPi)

When measuring current, there's a 250-ohm shunt resistor from the analog input to ground. This limits the voltage that the ADC sees to 5V when the loop current is 20mA. So there's nothing wrong with powering a properly configured loop with 24V. The loop itself will drop the remaining 19V.

-Phil

BCGary

Thanks Phil...much appreciated!

BCGary