Disposiable camera flash modification

[HarveyH42]

Hi, I'm building yet another cat scaring gadget, and could use a little help...

I've gotten this project down to the final stage, and not too sure about part selection, or the best way not waste too much battery power. I have a disposiable camera flash board, runs off of a single 1.5 AA battery. There are two switches (sets of wires...), one charges the capacitor and the other triggers the flash (when a tiny neon lamp glows and flashes "ready").

I just want to send power to the board, and have the capacitor charge, then trigger when the neon says its "ready". Nothing fancy, no need for variable rate or anything. Next I wish to a piezo-tweeter, so as to get a loud "POP" when the xenon fires.

Now, I'm pretty sure I can just shot the charge switch, but the trigger is the tough one, a neon lamp glows at 70 vac. I don't know how to pick the best part to trigger the flash with this.

The piezo-tweeter I have is rated 100 watts, hoping I can direct wire it to the neon or some place, maybe add a resister for protection.

Finally, this whole mess runs off 1.5 vdc, but my supply will be 9 volts from a PIR motion sensor, power by 6-nicad AAs , solar-charged. Need to drop the 9 volts down to 1.5, without wasting too much battery power. Although, the PIR will only power the flash board long enough for two-three flashes. So I guess its not to important right now.

The idea is a motion controlled electronic firecracker. Figured, I'd give this post a shot, and hopefully find some incrediably simple solutions.

finally note... I have read and search this forum pretty thoroughly, and...
Yes, I am aware that the flash board carries unpleasant charges, so yes I'll be very careful, and always discharge the capacitor, before touching the board.
I've search with Google and Metacrawler , there are several good pages for modifying these flash boards, but not what I had in mind. Some use exotic sounding parts for a variable rate stobe, others salvage the major parts, and build new circuits.
Oh, and this gadget should, in no way, interfer with cell phones....

 

[akg]

u could use a zener(6.3V) and 2 fw:biased diodes(2*0.6) to reduce the 9v to 1.5 v.

 

[1Steveo]

Use the pir to trigger an "Opto triac" ( MOC3020) to the Flash trigger switch.

 

[HarveyH42]

The output from the PIR powers the flash board for about 15 seconds, so I won't be able to use it to also trigger the flash... Also, when the PIR powers the flash board I hope to get 2-3 flashes each activation. Need the flash board to be self triggering.

Not positive about the zener diode suggestion, will play with it, and see if I can figure it out. The two forward biased diodes, could I use 1n914? I have about a thousand of them... I've got a couple dozen zeners some place, but never got around to sorting through them. Tough to read the markings....

Thanks for the help, sounds like one less problem....

 

[HarveyH42]

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Okay, this looks good in simulation, although the zenner blows up (program fault...) The acual zenner may differ, this was the only model in the program.

The trigger. Well, ordered some SCRs an NE-2 neons, like in most strobe circuits I've studied on the web, guessing it will work as expected.

The sound portion... I'm hoping a 100 watt piezo-tweeter will take some abuse... I've got a bunch, so no biggy if I blow a few up... no specs, and don't know much about ceramics.

 

[Nigel Goodwin]

Well, for a start, the diodes in the circuit are all the wrong way round!.

Secondly, piezo-tweeters aren't rated in watts, but in volts, I would suggest (as you've got plenty of them) using multiple ones in series.

 

[HarveyH42]

Alright. I got the flash board working as a strobe. It was real simple, just put anode and gate of a 2n5064 SCR across the little neon, the cathode to one of the trigger switch leads (not the ground side). It's a little faster than expected.

No luck on using 9 volts yet, even tried a resister voltage divider and 9 volt battery (might not have been fresh enough, just handy). Have to see why this flash board is so picky.

The piezo-tweeter... I hooked it across the neon, it clicks pretty good, but it interfers with the flash being triggerd. Not the load POP I wanted.

Oh, here in america, stereo equipment is usually rated in watts, thats why the speaker is rated at 100 watts.
Anyway, was going to try to hook it across the trigger transformer and ground, but the wire on the xenon tube side is sealed. The wire on the very small transformer looks a little delicate to mess with...

Hopefully, have these final issues worked out over the weekend. Thanks for the help.

 

[Nigel Goodwin]

Oh, here in america, stereo equipment is usually rated in watts, thats why the speaker is rated at 100 watts.

Stereo equipment is rated in watts everywhere, but NOT piezo tweeters, as 'watts' don't really apply to them.

 

[HarveyH42]

Well, here's all the info I got on the speaker...

GOLDWOOD GT-400CD BULLET PIEZO HORN DRIVER * Similar to KSN1142A * Power handling: 100 watts RMS. * Frequency response: 1800-30000 Hz * SPL: 92 dB 1W/1m * Mounts to any 1-3/8", 18TPI horn * Designed for use with our horn * Net weight: 1/4 lb. * Manufacturer model number: GT-400CD * Dimensions: diameter: 2-7/16", depth: 1-1/2".

They were cheap, and well into the ultrasonic range, unfortunately not all animals are effected by this. Some cats are just plain stuborn. I tried several frequencies, timing, and sweeps. Still have trouble with two male cats from across the street. If the strobe light doesn't do it, might try a little shock theropy (sp). The strobe board ought to give a nice jolt when they urinate in my carport...

 

[evandude]

yes, first off, you have all the diodes in parallel, instead of in series... the zener should be reverse-biased (cathode to + terminal of input) and the other diodes forward-biased. It wasn't a "simulation error", if you built that circuit you would in fact blow up all of the diodes.

Secondly, using diodes in that way to drop the voltage is not a good way to get a 1.5v output, since they are a fixed voltage drop... as soon as the nicads start discharging and their output voltage drops, your output is going to fall right with it, and even a little drop in each battery would be a significant drop as a fraction of the 1.5v output you want.