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Friday, 8 June 2012

Decision Maker With Slow Down Veroboard Stripboard

I've wanted to make one of these for a while, I am terrible at making decisions - if someone asks me anything where I need to make a decision I freeze up so over the years I've made various yes/no machines but they were never quite right because they didn't slow down, they just stopped. 

This is quite a simple little circuit, so simple I don't know why people haven't done it before - sure there are heads or tails type decision makers out there but they light up and stop when you release the switch where as this one slows down to a stop which feels more random than the other method.

the main difference between this circuit and the usual heads and tails circuit (which I got from my 130 in one electronics project lab) is that this one charges the 22u capacitor which discharges through Q1 basically lowering the voltage to the 555 oscillator, as the voltage lowers - the oscillation gets slower and as it depletes it stops on red or green - or whichever colours you choose

when you turn it on for the first time you'll notice that one of the lights are lit - this is normal.
the explanation for this is that the CD4013 is a dual integrated flip flop circuit so it's always in one state or the other - it usually starts up in the same state every time.
when you press the push to make switch both LEDs will light up, maybe with a little flicker and once you depress the switch they will start to slow down till they make their choice.

operating voltage is between about 6 - 9 volts any lower it will tend to favor one state over the other.

C5 - in the schematic, this was left out of the stripboard because it's not really needed so don't worry about this. I thought there might be an issue with DC hum but there wasn't

TRANSISTORs - Although I stated BC549s in the stripboard, you can use most general purpose transistors like 2N3904s for example.

my rather unimpressive boxed up version


  1. Hello,
    I've been an electronic experimenter for years now. There has been a circuit as yours made, in the January 1972 issue of Popular Electronics, called "Heads N Tails" I can't recall the authors name, but, he used a few transistors and an SN7473 flip flop. I remember making it after I got out of the service, worked very well. Thank you for posting your version of the decision maker, can't wait to try it! Thanks again, David

  2. Hello,

    How is the SPST momentary switch wired in? On a related note, is it a SPST momentary switch?



    1. I used a push-to-make switch rather than a momentary, it helps more with the randomness of the outcome.
      these switches only have 2 pins so just connect a wire to each one - doesn't mater which way around.

      the other switch you see on my boxed one is just an on/off switch in series with the battery.

    2. Ah, that makes sense. Thanks!