# Can I use the oscillation frequency equation for this circuit?

I'm not really sure if this is a question that can be answered so I'm sorry in advance if it isn't. I've just started doing electronics on a breadboard and I'm making a "Mini Strobe Light" from Jaycar's 'Short Circuit 2':

The book says that the first IC 555 (IC1) is a basic oscillator and that the second IC 555 (IC2) is a monostable multivibrator. I was going to use an equation for oscillation frequency (1.44/((R1 + 2*R2)*C1) to determine the flashing frequency of the LED. However, the book said that the potentiometer (circled in red) is not R2 and makes up R1 with the 33k resistor and that the circuit does not have a R2. On top of that, I'm not really sure if this equation is relevant as I thought that the LED flashes because of the output it receives from IC2. So I was just wondering if I could use the previously mentioned equation?

I'm really sorry if this is extremely longwinded but thank you to anyone who tries to help!! Please tell me if I haven't explained anything enough.

• You might want to look at a few tutorials on basic 555 astable and monostable circuits. The 555 is one of the most well documented and versatile basic chips in existence. It doesn't do anything exceptionally well, but is very versatile and educational.
– K H
Jan 14, 2019 at 2:53

It's more like the circuit sets R2 = 0$$\\Omega\$$. The consequence of this is that the first 555 will have a very short output pulse, and that it may not be very reliable over temperature and part variations.

The equation for oscillation frequency should still be accurate if you plug in a zero value for R2, though.