I did a mod today to the circuit to change it from 1/3 and 2/3 to 1/4 and 3/4.Side question. If Wally's circuit trips at capacitor voltages of 1/4 and 3/4 Vcc, and a 555 trips at 1/3 and 2/3 Vcc, why are the equations for the operating frequency the same?
Is that your teacher? So this is a homework problem?but i need to use 555 timer to do that as my doctor request from me
Okay, back to the 555 circuit.
You can use two 555's (or one 556) to generate a 1kHz PWM circuit from the variable resistance of the LDR.
Is that allowed by the doctor?
The first is configured as a 1 KHz astable multivibrator, adjusted to give a short negative going pulse.
This triggers a second 555 configured as a one-shot multivibrator with the LDR resistance controlling the one-shot period.
This will give a 1kHz signal out from the second 555 with the duty-cycle controlled by the LDR resistance.
First, let me correct myself in post #4. The constant in your equation is not the same as the one for a 555 astable (memory burp). However, it is the same as the one for a CD4060 oscillator section. In any case, I do not think it is correct for the circuit you show.What do you think the equation should be?
I tried what i understood ^^Show us your results and we will help you with any questions or problems you may have.
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by Lianne Frith