On Wed, May 26, 2010 at 9:19 AM, RussellMc wrote: > > > A safer value is usually 0.1 ohm. This gives 0.1 mV per mA or 0.1 V > per A. Many modern multimeter's have a 200 mV DC Volts range with a > resolution of 0.1 mV. On this range the meter v will read on mA. > > Also, using an eg 100 uF capacitor from the circuit's +ve to -ve > supplu leads at point of attachment often makes things work better. > > > Russell > > This reminds me of a circuit I recently used in a test fixture. I used a 10 ohm resistor in series with the load - the device is very low power. I measured the voltage across the resistor with an MCP3551 - 21 bit A/D converter (22 with sign), 3v reference. The theoretical LSB resolution is very small. I would guess that the accuracy is better than most transimpedance amplifiers of similar cost. You need an external A/D converter anyway if you want to measure a high dynamic range with your embedded circuit. The circuit I outlined can measure from a few microamps up to 0.3 amp, though the realistic limit depends on resistor dissipation. -- Martin K. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist