Measuring negative Voltages
Alan B. Pearce email (remove spam text)
>Would it be silly of me to suggest a current mirror?
>A pair of transistors, and a couple resistors.
Well I thought of a current source and resistor, which at the most negative
voltage gives an output voltage close to 0V, and at minimum required
negative voltage gave close to 5V - IIRC he was looking to measure -15
to -10V. Only problem with this arrangement is that it gives an upside down
A current mirror would be nicer if the measurement range did not scale 1:1
to the ADC range, and also has the advantage that minimum negative
corresponds to minimum positive input to the ADC.
See also: www.piclist.com/techref/power.htm?key=voltage
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