Electronic Decision Maker - 4046




In this instructable I will show you how I made an electronic "decision maker" with the 4046 - phase-locked loop.

What does that mean you ask? Well it's basically a coin flipper. You press the button to start the oscillation and then wait until one of the LEDs stabilizes.

If you need to decide between more than two states then you might be interested in electronic dice that I made in the previous instructable : Electronic dice with slowdown

Step 1: Demonstration

I was assigned to build this circuit at our school's electronics hardware competition by the name Zenit and with this layout I scored the first, although this was only regional round.

Step 2: Parts List

For this instructable you will need:

Decision maker PCB or some perfboard

1x - 4046

1x - 3.6V zener diode (can be omitted but then change R6 to 10k otherwise it won't behave properly)

1x - BC557 or any other small signal PNP transistor

1x - BC547 or any other small signal NPN transistor

1x - 1N4148 or any other general purpose diode

1x - tactile switch (I recommend the bigger one)

1x - 9V battery clip (6f22)

2x - 22µF/16V electrolytic capacitor

1x - 100nF ceramic capacitor

2x - 1kΩ resistor

1x - 2.2kΩ resistor

2x - 10kΩ resistor

2x - 100kΩ resistor

1x - 220kΩ resistor

1x - 1MΩ resistor


1x - 16pin DIP socket

Step 3: Schematic and PCB

You can use a DC power supply in the range of 3-15V.

To make the schematic and the PCB I used a free program Cadsoft Eagle which I would recommend to anyone making schematics or PCBs.

Step 4: Etching the PCB

I did not make the video.
I etched the PCB with i guess "photographic method" - that would be the direct translation from my language. I printed out the PDF file from previous step on transparent foil and then shone through it on photosensitve PCB, then developed it in solution of sodium hydroxide and then etched it in ferric chloride. If you find it confusing just watch the video, It's very well explained. Also don't forget to orient the transparent foil on the PCB so that you can read the words written on it.

Step 5: Perfboard Version

This project is ideal to build on perfboard because of it's simple layout. So if you can't make your own PCBs you can still build your own decision maker! I also cut the top and bottom borders with an utility knife to make it a bit smaller.

Step 6: Conclusion

This was probably the most symmetrical PCB layout I've ever made and also won a competition with.



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    9 Discussions


    1 year ago

    Hi! I did it but i have one problem and its the leds only are turn on but they dont blink
    or do something, Im using the circuit CD4046BD maybe thats the thing that doesnt work, I hope you can help me.


    2 years ago

    wow i cant believe you did that at 17! I'm 14 and looking for ideas for projects for my trade in high school do you mind if i borrow this?

    1 reply
    DIY Circuitseltoro5

    Reply 2 years ago

    I encurage you to do so. When I was at your age and even now I still look for ideas for projects on the internet.


    2 years ago

    Thanks a lot DITY Circuits, I could manage to get it for free.

    It is not very intuitive, I will have to grab a tuto.


    2 years ago

    Hi and congratulations.
    I tried to download Cadsoft Eagle but it doesn't seem to be free.
    Are you sure it is free ?

    1 reply
    DIY CircuitsPifouni

    Reply 2 years ago

    There is a free version but the PCB size is limited(100x80mm). I think it's called the express version.


    2 years ago

    did you design this circuit yourself? And how old are you if i may ask?

    1 reply
    DIY Circuitsnemob

    Reply 2 years ago

    No, I did not. As I said I was given this schematic at the school electronics competition and my task was to design a PCB. This circuit sold as a kit (Velleman MK135) and I think that is the original schematic and they have just redrawn it into eagle.
    I'm 17 years old.