Astable multivibrator - how to modify the timing

[Richardcavell]

Hi everyone.

Today I built this circuit, with a difference. I put pots in series with each of the resistors. It oscillates at about 2 hertz.

1. What's the standard method of varying the timing of the circuit?

2. Is it usual to vary the capacitance in a circuit like this? I thought of switching between a 10 uF and 22 uF cap, or switching a second 10 uF cap in parallel with each, but it seems easier to vary the resistance.

3. Varying the 47k resistors makes a huge difference to the timing. But what does varying the 470 resistors do? It seems to alter the brightness of the LED but doesn't do anything to the timing.

Richard

 

[MrAl]

Hi,

The 470 ohm changes the current through the LED and hence the brightness.

If you go too high with the 47k it wont be able to turn the transistor on enough.

Best way to vary the timing is with the capacitors, unless you need fine control then you can vary the 47k somewhat. You'll have to test to see what you can get away with with the 47k resistors.

 

[colin55]

The easiest way to adjust the frequency is to change the 47k resistors. They can be 22k to 100k.
The capacitors can be 10u to 100u.