Electronic Voltmeter Ammeter Circuit Using Single IC 741

Simple Electronic Multimeter High cost deters many hobbyists from buying a conventional multimeter. Since it is difficult to obtain cheap 50 uAor 100uA meters which are essential for a highly sensitive multimeter, an electronic alternative device is suggested to serve the purpose. The circuit shown here gives economic and safe ranges covered to th
Electronic Voltmeter Ammeter Circuit Using Single IC 741 - schematic

ree values : (i) 0-15V, (ii) 0- l5mA, and (iii) 0-150mA. The ranges can be extended with suitable modifications. The 741 operational amplifier acts as a null detector. its output is equal to the voltage at point A minus the voltage at, point B, multiplied by the device`s very high voltage gain. lf VA is slightly greater than VB, the output is limited by the supply voltage to about 7 volts. lf VA is slightly less than VB, the output is about 2 volts. At the point at which the output changes from low to high or vice-versa, VA is equal to VB to within a very small margin of error. With the switch set to the position shown in circuit diagram (15V range) the potential difference between points A and C is The forward voltage drop of the diode D3 is about 0. 6V and largely independent of battery condition. About 0. 5V appears across the variable resistance VRl and a known fraction of this indicated by a scale on the potentiometer appears between points A and C, i. e. it compares the known reference voltage with a known fraction of the input voltage. On the two current ranges, the reference potential difference is compared with the voltages developed across R4 plus R5 on the l5mA range and R5 only in 150mA range. T `D2, a light emitting diode, with its current limiting series resistor R9 indicates whether the output of the operational amplifier is high or low. The diode D1 and the condenser Cl provide the facility of measuring...

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