High impedance DC voltmeter.

admin August 17, 2009 4 Comments

Description.

A high impedance DC voltmeter using a uA741 IC is shown here. The operational amplifier is used as a non-inverting DC amplifier in which the negative feedback is through a DC meter requiring 1mA for full scale deflection. Since R6 is 100 Ohms, the meter will show full scale reading when the DC input voltage to pin3 is equal to the voltage drop across R6, viz 0.1 volts. Choice of R1 and R2 for getting different voltage ranges are shown in the table. The diodes D1 and D2 protect the IC from accidental excessive input voltages and diodes D3 and D4 protect the meter from overloads.

Circuit diagram with parts list.

high-impedance-dc-voltmeter

Notes.

  • Assemble the circuit on good quality  PCB or common board.
  • Mount the IC on a holder.
  • The circuit can be powered from a +9V/-9V dual power supply.
  • The meter M1 can be a 1mA FSD DC ammeter.
  • The values of R1 & R2  for different voltage ranges can be obtained from the table  given below.

Values of R1 ,R2 and the corresponding ranges.

high-impedance-dc-voltmeter-table.JPG

Comments
  • Ced
    August 17, 2009

    I think D2 is upside down, can someone confirm, the input is not protected against highly negative voltage. Current will be limited by R3 but not the voltage

    • admin
      August 17, 2009

      yes you are right. That was a mistake while drawing the circuit.
      I have corrected it.
      pls have a look

  • Rohit Pipalia
    February 26, 2009

    I am looking for a low volt regulated power supply.It should be adjestable from 1.5vdc to 12 vdc output.

    Rohit pipalia

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