Welcome to the N1IR Electronics Website. Totally off the cuff, one take, unrehearsed video projects for anyone interested in amateur radio, electronic design, makers, hardware hackers and science.

Get off your duff and build something!
Training the hand and mind since 1982.

Sunday, May 8, 2011

Current to Voltage Converter

I designed this for our Arduino based triple power supply. The supply is a bench top linear supply with a 20X4 LCD screen. Displayed on the screen is voltage V1,V2 and V3. Easy enough to monitor with the Arduino A/D converter with a basic voltage divider. However to monitor current we needed a current to voltage monitor, I searched the web and found some current to voltage monitors but there were not cheap, cost was around 30 bucks. My design this cost around $5 USD.

The heart of this circuit is the LMP8603 a 60V Common Mode, 100 x Gain Bidirectional Precision Current Sensing Amplifier
. With a very small value resistor to get around the burden voltage. I used a .01 ohm resistor that could measure 0 to 5 amps at 0 to 50mV across the resistor then added the LMP8603 with a gain of 100 so for every amp I would get 1 volt out.

The great thing about this IC, it's bi directional, it can be a high side or a low side configuration. It uses a single supply, A set gain of a hundred with no precision resistor needed like standard op amps.

Resolution of this is around 5V(A) / 1024 (10bit A/D) = 4.8 mA per step, if you need to change the resolution you could always swap out the resistor with a .1 Ohm but you maximum current would only be .5 amps, but resolution would increase to .48 mA per step. For my case I chose the .01 ohm.