Oscillator Circuit

The first stage in the HERF gun is to generate a frequency which will be used to create alternating current to pulse the ignition coil with. The best circuit for this application uses a 555 timer IC. A crudely drawn circuit is below.

The right side also shows the ignition coil driver. R1 and R2 are 100 K potentiometers (variable resistors), each in series with a 4.7 K resistor. These allow the output frequency to be adjusted. The 555 timer provides output current on pin 3, up to 200 mA. The parts used for this circuit are (with RadioShack numbers):

• 276-158 Grid-Style PC Board
• 276-1723 LM555 Timer
• 271-092 100 K ohm Linear Taper Potentiometers (two needed)
• 271-1330 4.7 K ohm 1/4 watt resistors
• 272-1069 0.1uF 50V Polyester Film capacitors
• 276-1995 8-pin socket for the 555 IC

The possible frequencies are dependent on the capacitor labelled 'timing capacitor' in my diagram, and the resistors. For the values shown here, the frequencies range from 46 to 1023 Hz.

The ground and output from this circuit feed into the next step, the ignition coil driver.