74 as seen in fig5 a fig5 a and 5b show the microcontroler and associated digital to analog converter portions of the circuit while any suitable microcontroler may be used a 87c750 from phillips is preferred microcontroler 74 provides the necessary timing and control for the generation of the variable signal through jack 22 fig3 the output 34 on 34 time periods the 34 on time 34 selector and the mode control selection the output from pin 6 of the microcontroler is the output on signal to the base of transistor 76 fig7 typically a 2n4401 from motorola which in combination with transistor 78 typically a 2n4408 from motorola controls the output on off condition that condition is selected by the 34 on time 34 selection switch 38 by turning on and off the vcc voltage to the output power amps integrated circuits 80 fig7 b and 82 fig6 b each typically a tda7052a from phillips the input signal to pin 18 of microcontroller 74 is the 1024 u03bcs clock from the clock generator and is used for the interrupt timing control of the microcontroller integrated circuit 84 fig6 a typically a 74hc4060 from motorola is a 14 bit binary counter and oscillator used to provided the necessary primary clocks required for system operation a 4 mhz crystal is connected between pins 11 and 10 of.