- Blog entry posted in 'General Purpose Circuits.', May 07, 2012.
This is a simple circuit for converting a 4mA thru 20mA Loop signal to 0V thru +5V, suitable for an ADC input.
When using a LM358 OPA, the closest specified lowest swing is approx 20mV above 0V.
Take care when using with a ADC that will not accept excessive outputs voltages from theLM358.
For example with a PIC if the OPA output could exceed 5V in operation, using a limiting resistor, that will limit the ADC input current to less than ~10mA.
The internal clamp diodes of the PIC are rated at ~20mA max.
A series 470R connected between the LM358 output and the ADC input pin will limit the clamp current to ~10mA, if the OPA output reached +10V.
NOTE: 16 May2012
Added a 0V to +10Vout version of the converter
NOTE: 17 May2012
Added a 0V to +5/10Vout version of the converter for a 0mA to 20mA input.
korak_de, May 14, 2012
Hi, Neat circuit. Would it be possible to modify the circuit to give a 0 thru 10V output. For your circuit, I guess another alternative would be the RCV420 IC.
ericgibbs, May 14, 2012
hi korak, As requested a 10Vout version has been posted. E.
korak_de, May 15, 2012
Dear Eric, Thanks for the quick reply. These circuits are really neat. The beauty lies in the simplicity with which you have achieved the conversion. I will try them at the earliest. Keep up the fantastic work Korak
Acquired Engineer Lucky, June 07, 2012
Micheal_Up, December 03, 2012
Hi Eric, I agree all reply here. There are more informations about LM358-serials just click [URL="http://www.hqew.net/product-data/LM358N/"]here[/URL].