![]() ![]() The amplitude of IC3’s inverted output available at CON5 can be adjusted using potmeter VR4. These frequencies are also available across CON4 at pins 3, 4 and 5, respectively. That is, the output frequency of IC2 is divided by 10, 1. Resistive dividers comprising R11 through R14 provide three more amplitudes. The amplitude of signals can be adjusted using potmeter VR3. The frequency signal output produced by IC2 is available at connector CON4. ![]() Here, forward resistances and voltage drops of diodes D3 and D4 are neglected and inverse resistances of diodes assumed to be infinity. When Cx=1nF and VR2=0-ohm, the maximal frequency (Fmax) is: Where Cx may be 1nF, 10nF, 100nF, 1♟ or 10♟.Īssuming switch S1 is closed and Cx=1nF and VR2=22-kilo-ohm, the minimal frequency (Fmin) is given as below: The frequency (F) is determined by components connected to pins 2, 6 and 7 of IC2 as follows: Table below shows calculated frequency ranges of squarewave signals. The signal generator produces forward and inverted signals through IC2 and IC3, respectively. It is built around two NE555 timers (IC2 and IC3), an LED (LED3), seven BAT42 Schottky diodes (D3 through D9) and a few other components.įig. The circuit diagram of the signal generator is shown in Fig. The variable power supply can be used for additional adjustment of the timers’ amplitude. You can vary the output from 1.25V to 15V using potmeter VR1. The 4.7kΩ resistor(R2) is a pull up resistor.įor the schematic and PCB I used a free program CadSoft Eagle which I would recommend to anyone making schematics or PCBs.The power supply output available at connector CON2 is variable. The 1kΩ resistor(R1) limits the base emitter current, without it the path from pin 7 of the IC to transistor would act like short circuit to ground. ![]() In other words the PWM signal is amplified by the transistor. The PWM signal generated by IC switches the transistor on and off. We have to use a transistor because the NE555 is not capable of supporting high currents to the load so the majority of current goes through transistor and not the IC. The oscillation is determined by the size of capacitor(C1) and position of potentiometer(R3). The integrated circuit NE555 is wired in an astable mode(oscillator). But if you used separate power supply for the chip and for the transistor it could be used for driving voltages higher than 16V. HOW IT WORKS This circuit can work on voltages from 4.5V to 16V. A big advantage of this board design is that it can be plugged into the breadboard for testing. ![]()
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