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
The 1/4 - 3/4 version. As dangerous as this is to say out loud, I think your frequency equation is incorrect.I did a mod today to the circuit to change it from 1/3 and 2/3 to 1/4 and 3/4.
Which version are you looking at?
Well, I was lazy and just derived the formula empirically from the simulation, so no guarantees.The 1/4 - 3/4 version. As dangerous as this is to say out loud, I think your frequency equation is incorrect.
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.
Is this homework?Could you provide me with a schematic ?
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?
Yes ..Is this homework?
Show us your results and we will help you with any questions or problems you may have.I will try to build a circuit and then post the result here
My empirical calculation gave a value of 2.2, so that's close enough for government work............
Now, 0.25 and 0.75 trip points --> 2.47.
I tried what i understood ^^Show us your results and we will help you with any questions or problems you may have.
by Jake Hertz