Im building a multi-channel firework ignition controller.

My hopes are to have 6 selectable channels (each connected to a diff firework). each channel is turned on/off by a spst toggle and each also has a red indicator lamp that will light when channel is on.

the issue i am having is that i want the red lights to double as continuity indicators as well. i want a spdt toggle to select a fire circuit or a test circuit.

i have a schematic drawn but am unable to uploaded due to the file type. i can email it to anyone who thinks they can help.

really my question is this: i want to run 20mA thru the test circuit to test the continuity w/o actually lighting the fireworks. im powering the controller with a 9v battery and using a 1/4w 470 ohm resistor for the test circuit. will 20mA be enough to light the 12VDC lamps that i will be using as indicators?

i really appreciate any/all help. thx

 

You should use leds as the indicators opposed to a 12vDC bulb. It will take much more to light it.

Depending what you are using as a match, but you could use a very low wattage resistor. If you pass a few volts a few mA, you could light the led. But if you draw more, you can ignite the resistor, using it as the match.

Can you take a screen shot of the schematic and post it? Try to save it as a PNG.

 

a match.....

but I think it has already been invented

 

I think Retched was talking about overloading the resistor and using it to ignite the fireworks. When a resistor overload it tends to burn its surroundings. It would be a one time use component though, you'd have to have a supply of resistors. The advantage of this is that you can light the LED with a low voltage and fire the fireworks with a high voltage (which won't last for long because the resistor will burn out in seconds.) You may need a zener diode to limit the current that flows through the LED when the higher voltage is selected, because for a few seconds the LED will be faced with more voltage than it is rated for.

 

ok i hope this works... heres the schematic. (keep in mind im a novice )



i had thought to use leds at first but i figured with my design, wen i pushed the fire button, the leds would overload and fry... maybe im wrong.. idk

thx again for the help. reeeeally appreciate it!

 

Uhhh, no. You do not want the LEDs in series with what is probably a pretty high current path. Be right back, drawing.

This is a fundamental circuit used for rocket launchers (very similar application). The toggle switch is a safety switch. Many cases it is a earphone jack that uses a shorted earphone plug, so some manjack can't activate it while you are working on the other end.

 

that really helps alot. but..... i really only want 1 fire button that would fire all selected channels...

i went back and made some changes to my schematic using your diagram as a template and came up with this


the problem is i dont think the indicator lights are true to indicating continuity in their given channel.. there could be cross contamination from other closed channels.

i feel like im getting closer and i really appreciate the input. keep it coming. thx

 

You are right, it is a major problem. How about putting the arming toggle switches across the resistor/LED, and have the "fire" button up the chain? When you arm a circuit the LED would go out, but you still have the option to test continuity. Just label the two positions "test" and "armed".

Something like this...

 

i thought of that too and was very tempted by it... but i did not like the idea of the LEDs going off when it was switched to "armed" and after reading the quote at the bottom of your posts, i couldnt settle for just "good enough"

so i went back to the drawing board and i think i may have solved that problem and the problem of cross contamination....



any concerns?

 

I think that would work, but be sure to overrate the diodes. 1Amp is still low for what I suspect those ignitors will use.

 

so what kind of diodes do i need? im still pretty new to this stuff and dont know anything about diode ratings...

 

From what I've read you need high current. Try one of your ignitors out of circuit and see what the current draw is. You need to know this for the switches too.

What are your ignitors? Were do you get them?

 

the ignitors are homemade. just a strand of 44g nichrome wire between the ends of some 22g speaker wire. im gonna clip the nichrome right against the firework fuse.

 

OK, do it dry (without the circuitry, just the battery) and see what the current is. I figure you have a DVM with a current meter.

 

ok. thanks for all of your help!