Need help with a Fireworks project I'm working on - Electronic Circuits Projects Diagrams Free

Triskal · 22nd March 2008, 04:34 AM

I've been working on a Computer controlled firing system for fireworks, and I thought my design was going to work... all my breadboard tests worked great, so I built a PCB, and now a problem has surfaced... went back to the breadboard, and sure enough the problem has been in the design all along. Without boring you completely with the intricate details of the control.. here's my problem.

The Plan:
The plan was to use P-channel, and N-channel MOSFET's in series, one that would switch the ground, and the other that would switch the positives. This would allow me to have 8 n-channel mosfets switching the grounds, and 8 p-channel mosfets switching the positives... turning any two at a time on, would turn on a different combination of circuits, and eventually lighting a firework.

The Problem:
The problem seems to be that whenever I turn on one of the P-channel mosfet's, all the LEDs turn on (using LED's in place of fireworks for the time being... don't really want to blow myself up), regardless of what's going on with the n-channel ones. The most extreme case I tried was turning none of the n-channels on, and 1 of the p-channels on... and all the LEDs turned on. What I don't understand is why this would happen and how to fix it.

Attached is a simplified schematic of the circuit...

Any help would be appreciated.

Thanks

ldanielrosa · 22nd March 2008, 05:39 AM

Perhaps the circuit you included is over-simplified, and perhaps I'm not reading clearly at this hour. What I see is two N-channel and one P-channel, both biased on, with no explicit indication as to what the inputs actually are. Am I missing something here?

Triskal · 22nd March 2008, 06:26 AM

it's possible that the diagram is over simplified. The inputs to A and B are a 595 IC, which is controlled by the parallel port of my PC. The input to C is a 595, who's outputs go through a ULN2803 to reverse the output (595 sends a high, ULN2803 sends a low, and vice versa).

I'm not sure what you mean by biased on? the 10K resistors on A and B are pull down resistors, pulling the turning the gate off, and the 10K resistor on C, is pulling the gate up, which turns it off.

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22nd March 2008, 05:39 AM	(permalink)
ldanielrosa	Perhaps the circuit you included is over-simplified, and perhaps I'm not reading clearly at this hour. What I see is two N-channel and one P-channel, both biased on, with no explicit indication as to what the inputs actually are. Am I missing something here?

22nd March 2008, 06:26 AM	(permalink)
Triskal	it's possible that the diagram is over simplified. The inputs to A and B are a 595 IC, which is controlled by the parallel port of my PC. The input to C is a 595, who's outputs go through a ULN2803 to reverse the output (595 sends a high, ULN2803 sends a low, and vice versa). I'm not sure what you mean by biased on? the 10K resistors on A and B are pull down resistors, pulling the turning the gate off, and the 10K resistor on C, is pulling the gate up, which turns it off.