| Description:I was wondering if you could make a Voltmeter that could also tell you the contactresistance it was measuring from (giving you the Theveninmodel of the source). I implemented something simple using an Arduino+LCD shield and 4 resistors. As a bonus it also tells you how much 50Hz is present on the measurement (I had to average powerline cycles anyway). Although my meter has 1Mohm input resistance you can see below that measuring on a source with 1Mohm contact resistance the voltage measurement error is only 1% compared to measuring direct and the contact resistance is measured correctly. |
| measuring an (almost empty) 2xAA batterypack via a 1Mohm resistor: Reading shows: -2831mVdc, no 50Hz and 1004 kohm contact resistance.  |
| measuring an (almost empty) 2xAA batterypack via a 0ohm resistor: Reading shows: -2799mVdc, no 50Hz and 0 kohm contact resistance.  |
| Info: circuit description and calculations |
