Simple Square wave Generator

Three switchable frequencies: 100Hz, 1KHz, 10KHz
1.5V battery operated, minimum parts counting

This simple circuit generates a good and stable 1V peak-to-peak square wave at 100Hz, 1KHz and 10KHz using a single 1.5V cell as power supply.

An useful feature of this circuit is that frequency changes can be obtained by switching only one capacitor at a time. Current consumption is about 600µA.

Parts:

• R1____________560K 1/4W Resistor
• R2____________680R 1/4W Resistor
• R3______________2K2 1/4W Resistor
• R4____________150K 1/4W Resistor
• C1_____________12nF 63V Polyester Capacitor
• C2______________1n2 63V Polyester Capacitor
• C3____________120pF 63V Polystyrene or ceramic Capacitor
• C4,C5__________10µF 25V Electrolytic Capacitors
• Q1,Q2________BC549C 25V 100mA NPN High-gain Low-noise Transistors
• SW1____________SPST Slider Switch
• SW2____________1 pole 3 ways Rotary Switch
• B1_____________1.5V Battery (AA or AAA cell etc.)

Notes:

• If a precise 50% duty-cycle is needed, trim R1 and monitor the output wave form by means of an oscilloscope.
• A good 500mV peak-to-peak square wave is provided even at 1V supply.

Self-powered Sine to Square wave Converter

Converts sine to square waves without a power-source
Useful as a test instrument for audio purposes

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.


Parts:

• 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

Notes:

• Best performances are obtained with an input sine wave amplitude from 1V RMS onwards.
• Output square wave amplitude is proportional to input amplitude.
• Minimum sine wave input amplitude needed for good performance: 750mV RMS.
• Output 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.