electronic head tail schematic

Electronic Head or Tail Circuit

The principle used in this electronic head or tail circuit is simple: a multivibrator controls a flip flop. The multivibrator oscillates as long as the buton S1 is pressed and the flip flop switches on and off with a frequency of several kilohertz. When the button is released, a +5 volts is set at one of the two gates that makes up th multivibrator. The flip flop latches on at one of the two possible states: “head” or “tail”.

The state of the flip flop is dependent on the exact time when the button S1 was released. because the speed of the flip flop’s switch overs and the relative inertia of the human reaction, the state at which the flip flop latch is random.

The entire circuit is made up of a single 7400 IC. It is important to decouple the circuit and the display bulbs very well to avoid reverse voltages and currents that appear during the switching off of the display bulbs.

The capacitor C5 (not shown in the schematic diagram) is a 250 uF electrolytic capacitor rated at 10 volts.

Electronic head or tail circuit schematic

electronic head tail schematic

Head or tail PCB layout

electronic head tail pcb


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  • AlanC


    I build this circuit in the 70s and it did not work.

    I have played around with it in a simulator and the oscillator inputs need pullup resistors between 1K and 10k (say 2.2k) in addition the the 1k resistors (see image).

    The flip-flop misses pulses (works better with LSTTL and 4k7 resistors rather than the 10k resistors) but in this circuit who cares.

    Regards AlanC

    • AlanC

      Hi All,

      I think I know what is going on here.

      The old TTL devices probably had reverse diodes between ground and the inputs as show in a typical TTL schematics. The new TT5L/LSTTL devices and the simulator model appear to be different?
      If I put a reverse diode in the circuit it comes to life in the simulator!

      Regards AlanC

  • bethellou castañeda

    hi saan po pwedeng makakuha ng schematic diagram ng mosquito repellent na may fun or blower?? tnx po