Electronic Circuits and Tutorials
Electronics Schematics - H

Amplifier Circuits: High Impedance Circuits

This schematic is the power supply and front-end sections of the field monitor that is discussed in more detail at Electric Field Disturbance Monitor. The system can detect human and animal motion by the electric fields they disturb.

High Impedance Voltmeter (Phototransistor Circuit Test Voltmeter) - This circuit is designed to provide an inexpensive way to to create a High Impedance Voltmeter while making use of an inexpensive analog or digital multimeter. The circuit is specifically designed for testing phototransistors when they are used in the circuits shown at this site. It has a very high input impedance that will not "Load Down" the sensor that is being checked.

High impedance inverting operational amplifier circuit - The standard inverting amplifier configuration is widely used with operational amplifier integrated circuits. It has many advantages: being simple to construct; it offers the possibility of summation or mixing (in the audio sense) of several signals; and of course it inverts the signal which can be important in some instances.

High impedance DC voltmeter - 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.

NoteTo report broken links or to submit your projects, tutorials please email to Webmaster