A square wave generator is one of those pieces of equipment that has many uses in the workshop yet few hobbyists actually have. This simple kit, based on the popular 555 Timer IC, generates six preset frequencies from 1 Hz to 100kHz. It has a wide operating voltage range and even provides visual indication of the output.CIRCUIT DESCRIPTION
The circuit is straight out of the 555 data book. The 555 is configured for astable operation, meaning that it will trigger itself and free run as a multivibrator. The timing elements are resistors R1, R2 and one of the capacitors (C1-6). The capcitor is selected by placing a shorting plug on one of the jumpers J1-6. The selected capacitor (C) is charged through R1 + R2 and discharged through R2. This allows the duty cycle (on/off ratio) to be precisely set. The charge time (output high) is given by:
t1 = 0.693 (R1 + R2) C The discharge time (output low) is given by:
t2 = 0.693 (R2) C The total period is T = t1 + t2 = 0.693 (R1 + R2) C The frequency of oscillation is:
f = 1 = 1.44
T (R1 + 2R2)C The duty cycle is: D = R2
R1 + 2R2 For the values shown, the six frequenies generated are 1Hz, 10Hz, 100Hz, 1kHz, 10kHz, 100kHz. However, due to component tolerances in the capacitors, these frequencies can vary by as much as 10 percent. The duty cycle is approximately 50%. Capacitors C8 and C9 provide power supply decoupling. The kit has an operating voltage of 5 to 18VDC.