Electronic – arduino – Simulated 555 timer not working

Here is something to try. Q20 wants to be a phase splitter. You can read about that here; enter link description here. Because you are tying Q20's base directly to 9V it is not working like a phase splitter. It is two forward biased diodes BC and BE. The means both the base of Q21 and the input to the 200 Ohm resistor are at 8.3V. So try this, put a resistor between the switch and Q20 base. Size it to get say 1V at the 200 Ohm resistor. When you do this, you will get about 1.5mA flowing thrugh Q20 emitter. This same current will flow into the collector trying to drop about 10V in the 6.8k resistor. Since it can't the transistor will saturate at maybe 1.1V. Now you will have Q24 on and Q22 off. Driving the base directly with 9V has them both on.

First of all, try following a schematic rather than a youtube tutorial showing a breadboard. There is a good chance you may have wired something incorrectly.

A 555 timer in an astable configuration would look like this:

^{simulate this circuit – Schematic created using CircuitLab}

Using this, you should be able to place your components on a breadboard, following the schematic closely. I assume you know the internal connections of a breadboard, but just in case, here is a diagram:

If you change the values of R1/R2 or C1 then you will be able to vary the frequency. Or stick a potentiometer in the place of R2.

This link HERE will be able to help you calculate which values to use for your desired frequency.

If you wanted to work it out yourself, you could use the forumula:

f= 1.44/(R1+2R2)C

Although I have found that to be a tad off sometimes! But it gives you a ballpark idea as real world electronics will never be exact!

So, basically, take it apart and rebuild it, this time following a schematic!

P.S make sure you have a working LED!