Wireless firework control

[deanbayley]

Hi Guys,

I want to create a wireless firework igniter, don't worry its going to be used very responsibly!

Basically i need a circuit that will allow me to generate about 1.1a for about 2 seconds from as small a battery as possible.

I was thinking I'd need to charge a capacitor from a 9v cell? or could i use something even smaller/cheaper?

I'm not expecting anyone to do all the work for me (although any help is very much appreciated) I was just wondering if you guys might know where to start?

What is the circuit I'm trying to make called? If it was voltage it'd be an inverter, but as its current I'm trying to boost I'm not sure :)

Thanks in advance!
Dean.

[audioguru]

The voltage from a charged capacitor drops during discharge. If you charge a 0.5F (half a Farad) capacitor to 9V and discharge it for 2 seconds with an average of 1.1A then at first the current will be 1.65A, in 1 second the voltage will be 6V and the current will be 1.1A and in 2 seconds the voltage will be 3V and the current will be 0.55A.

I think a super-capacitor with a value of 0.5F will be huge.

The voltage from a 9V alkaline battery will start at 9V, quickly drop to 7.2V after a few capacitor charges then keep dropping each time it is used.

[deanbayley]

Hi audioguru,

Thanks for your quick and concise answer, I think that a capacitor of that size would be impracticable :(

I have been told i could use a decent (Duracell) 1.5v cell to provide the current for heating the coil, the only problem is finding a receiver circuit that will run from just 1.5v...

Any ideas? I could use 1x 1.5v and 1x 9v for the receiver and relay?

Where can i find a circuit for a long range transmitter receiver circuit that isn't easily triggered from interference?

Thanks!
Dean.

[audioguru]

There are transmitters and receivers that have a range of 100m. You would need to make a circuit to modulate the transmitter with a special code then another circuit at the receiver that would respond to only that code.

I have seen 1.5V Duracell tiny watch battery cells and huge 1.5V cells. The little ones won't last.

[deanbayley]

Hi audioguru,

Yeah i was meaning the AA type 1.5v, i have found this module (http://www.maplin.co.uk/Media/PDFs/N87BN.pdf) but i was wanting more like 500m range, what are my options in this situation?

Thanks!
Dean.

[audioguru]

I don't know of a transmitter/receiver that goes 1.5km. Garage door openers and keyless car remotes don't need such a long range.

Test a little AA cell to see how many times it can heat the ignitor coil.
Which gets hotter, the coil or the battery cell?

[deanbayley]

I have a pair of cobra 5km radios, would it be safe (won't damage the radio) to use the audio output from the radio to drive a transistor to drive the relay?

I was thinking of turning to the radio to full volume and using the radios call feature which generates a harsh tone which I'm hoping is higher voltage that would generated under normal voice operation..

This is the circuit i was thinking of: http://www.kpsec.freeuk.com/images/trswinpn.gif

Thanks.
Dean.

[audioguru]

Millions of people have those FRS radio walkie-talkies. You don't want to use something like that to ignite fieworks.

[deanbayley]

The site where i will be using the setup will be well out of the way from anyone that will using those radios, the remote trigger is more for effect than anything else, i would never trigger anything that couldn't be safely triggered by lighting the fuse...

There are 304 channels so there is little chance of someone being on the same channel...

Would i be risking damage to the radio?

I ran some tests, the radio has a resting audio output of about 0.5v and an active voice voltage of between 1.924 and 1.927v, pressing the radios call button gives a reading of 1.875v

Thanks!
Dean.