Self-poweredSine to Square wave Converter

Converts sine to square waves without a power-source

Circuit diagram:



R1_____________1M   1/4W Resistor
R2___________100K   Linear Potentiometer

C1,C2________100µF  25V Electrolytic Capacitors
C3____________10nF  63V Polyester Capacitor

D1,D2_______1N4148  75V 150mA Diodes

IC1___________4069  Hex Inverter IC

Device purpose:

This circuit is intended to provide good square waves converting a sine wave picked-up from an existing generator. Its main feature consists in the fact that no power-source is needed: thus it can be simply connected between a sine wave generator and the device under test.
The input sine wave feeds a voltage doubler formed by C1, C2, D1 & D2 that powers the IC. IC1A amplifies the input sine wave, other inverters included in IC1 squaring the signal and delivering an output square wave of equal mark/space ratio and good rise and fall times through the entire 20Hz-20KHz range.


  • Best performances are obtained with an input sine wave amplitude from 1V RMS onwards.
  • Ωutput square wave amplitude is proportional to input amplitude.
  • Minimum sine wave input amplitude needed for good performance: 750mV RMS.
  • Ωutput square wave amplitude with 1V RMS input: 3V peak to peak, with R2 set at max.
  • Minimum output square wave amplitude: 2V peak to peak, with R2 set at max.
  • Substituting the two silicon diodes with germanium types (e.g. AA118, AA119), the minimum input threshold can be lowered.

This circuit won £50 and was published on
ELECTRΩNICS WΩRLD “Circuit Ideas”, February 2000 issue,
page 135.

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