Measuring Resistance

This experiment measures resistance. You can get very low-cost digital multimeters to measure resistance and display the value on a four digit display. We cannot compare with cost and complexity of this type of display, but our circuit has other features. It will activate a device when a particular value of resistance is detected. This allows measurement of degrees of rotation of a potentiometer or the conductivity of a liquid (via two probes), plus many other areas where resistance values change. Our demonstration program uses a potentiometer to detect resistance in the range 0k to 10k however any other range can be read, by changing the value of C. The accuracy of the circuit is determined by the tolerance of C (most capacitors are 10%). The time taken to produce a low on the input is used as a jump value in a look-up table and a display-value is obtained for the 7-segment display. For simplicity, the values 0 to 9, plus "-" overflow, are displayed. Further experiments show two and three-digit accuracy.

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