# Voltage across capacitor...

#### ascotti

Joined Jun 7, 2004
2
Hi there,
I am trying to write a software emulator for some circuits that were used in the 80's to generate sounds and effects in arcade machine. You can check:

http://www.ascotti.org/programming/side/soundboard.htm

to see for example the Space Invaders soundboard.

I wonder if some of you can help with this piece of circuit:

V1+ --- R1 --- C1 --- R2 --- C2 --- R3 --- V2+

(all capacitors also connected to ground). I need to determine the voltage across capacitor C2.

What I'm doing now:
- I charge C1 via V1 and R1;
- I charge C1 via R2 and C2 (doesn't seem to matter much);
- I charge C2 via C1 and R2;
- I also charge C2 via V2 and R3.

The above doesn't seem to be correct, but with my limited knowledge I can't do better (I have read the relevant chapters of the great "All About Circuits" guide and worked out the examples up to the "Complex RC circuits" with Thevenin's theorem, but I don't know how to apply that to my case).

If possible, I would like a formula that gives me the voltage across capacitor C2.

P.S. I have attached a picture with the whole circuit (it's the "fire" effect from Galaxian by the way), the part I refer to is in the lower right corner.

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#### mozikluv

Joined Jan 22, 2004
1,435
hi,

where does the line of R46 & R48 lead to going upwards ( base on the picture you presented)

what's the voltage supply

what's that line connecting to the series R46 & R48 with a mark word (noise) :unsure:

#### ascotti

Joined Jun 7, 2004
2
The R46 and R48 lines go upward to (one of) the control of a 4066 switch that is unused in this circuit. We can assume the lines are disconnected.
The voltage supply is +5V and the NOISE line is connected to the output of a 7474.

#### mozikluv

Joined Jan 22, 2004
1,435
hi,

base on the picture R47 & R48 act as a voltage divider to C28. so whatever is the voltage ouput of pin 3 of the 7400 only half goes to C28.

C29 holds the voltage of pin 5 of the timer to 1/3 of the supply in relation to the threshold voltage of the timer.

as to the other circuit you have presented use the Kirchoff voltage law