Halloween circuits

[HarveyH42]

I was cleaning off my workbench (first time for everything) to make room for some new projects and found I had several items that would make great Halloween effects. Thought maybe this year I'd do something with them.

I have 3 disposiable camera flashes, converted to strobe (plus a bag full I never messed with). Never figured a good way to get them to run off anything besides 1.5 batteries. Wired in series, they worked okay off a 5v wallwart. Nice lightning effect, as the charge and flash at slightly different rates (10 to 15 seconds).

LED candle circuits (several attempts) for jack-o-lanerns, torches (not flashlight, like in the UK).

Fading Red Eyes, should start shopping for a cheap plastic skull or something...

Those are pretty much ready to use, just a few minutes to install. Was wondering if anybody has some quick and cheap circuit/prop ideas to add to the list.

 

[Nigel Goodwin]

EPE did a project last year, called "Halloween Howler", a PIC based circuit that played audio out of an EEPROM (up to 11 seconds worth). It was triggered by a shodow passing over the sensors - the idea being you walk past a skull and it talks to you!.

 

[HarveyH42]

I've had some ideas on animating a skull, but have run across one with a moviable jaw, not to mention they usually look a little cartoonish. Was going to use a single channel color organ type circuit to run a motor to work the jaw to audio.

I did pick up 3, 16meg MP3 players ($5 each), but haven't figured out how to pop them open without a hammer. Not very loud, but what do you expect from a single AAA battery.

 

[justwantin]

I tried a 5 LEDs for flickering light in a pumpkin run by a PIC based on this **broken link removed** but there really wasn't enough light to make it worthwhile until I changed it all to an array of 15 LEDs, three wired in parallel off each 5 pins on a PIC12F675 then bunched all up like a flower arrangement so that light from on LED's was also a secondary reflection in off LEDs.

I used 10 clear/yellow and 5 clear/red LEDs. A 4Ah 6V battery power supply was a winner as the brightest compared to a 1.3 Ah 6 volt battery and a 4.5V wall wart. I used an LM317 for a 4.5V supply off the battery.

I experimented with a foil lined box but the effect was even better and brighter in a 26-280mm paper mache pumpkin with inside painted bright white. The red Leds made a difference in reflecting off the white paint and'd probably be just as good in a real pumpkin

Not bells and whistles or complicated just allot of soldering. There's an avi of the effect in and out of the box here **broken link removed**

 

[HarveyH42]

Wow, this thread is 3 years old... Think it was just before I started messing around with AVR microcontrollers. I did an LED candle with a Attiny13, using 5 LEDs (3 Amber, 2 Yellow). Thought the red was a little out of place. Never tried it in a pumpkin, but its plenty bright. Found a pretty cool flicker method using Bascom BASIC, I just pick a pin at random, and toggle it, and small delay before picking another pin. Haven't noticed any periods of all pins off (dark). I'm also a little abusive, don't use any resistors on the LEDs, 4 AA batteries for the supply, no regulator. I mostly use NiMh batteries, but works fine off disposables (6 volts, fresh). The Tiny13 data sheet recommends 5.5 volts max.

 

[BrownOut]

Halloween must be one the greated times for hackers.

 

[giftiger_wunsch]

Halloween must be one the greated times for hackers.

Maybe for the kind of "hacker" who wields a machete, yes

 

[EN0]

Two years ago I made an awesome robot costume (if I do say so myself ). I had two red LEDs for the eyes and two blinking green LEDs for the antennas. I also assembled this voice synthesizer kit and used the "Robot Voice" mode. My friends and siblings were really jealous because I always got an extra handful of candy!

 

[giftiger_wunsch]

Did you have a car battery strapped to your back to power the lights?

 

[EN0]

Did you have a car battery strapped to your back to power the lights?

Nope, all I had was a 9V battery. It's lasted two years! I haven't used it much though, but It stays just as brilliant as ever.

 

[justwantin]

That's the beauty of LED's they use virtually nothing for what you get out of them. My 15 LEDs take up maybe .2V running around 8 hours.

 

[giftiger_wunsch]

How do you "take up 0.2V"? They dissipate energy during their operation; change in battery voltage over time is a poor measure of the efficiency of the LEDs as it's usually non-linear and varies greatly between types of batteries.

Measuring the power being used compared to light intensity, on the other hand, is a much better measure of efficiency as you're measuring energy over time.

Either way though, LEDs are typically more efficient than filament bulbs, true enough.

 

[justwantin]

The same way one takes ups space, or the slack hmmmm.... "take up energy" is just a figure of speech, not proper terminology. Let me put it another way. I had 6.5 volts last night I have 6.3 volts this morning. That's about as measured as I can get.

 

[giftiger_wunsch]

Voltage is charge separation, and as you discharge a battery the voltage falls in a non-linear way, so this is not a good way of measuring how much energy the LEDs have dissipated.

On the other hand, if you're using a 6.5V supply, and for example the current through the LEDs is around 200mA, then we can say the following:

a) In 8 hours, you've discharged ~1600mAh of the battery's charge

b) The LEDs are dissipating 1.3W of power, i.e. in 8 hours, the LEDs have converted ~37.44kJ of electrical energy into light (and partly into heat etc.).


That's a much better method of measuring the power requirements of the LEDs, and comparing the brightness to a 1.3W filament bulb, for example, would be a good way of checking its comparative efficiency.

Please note that I don't know the actual voltage / current across these LEDs so I've made an estimate.

Also note that I haven't used the phrase "take up energy": it's dissipated, i.e. dispersed into the LED's surroundings as light and/or heat.

 

[justwantin]

Thanks for that. I have taken up too much of your time ;^) Current would be a tough one to measure as the LED's are spec'd slighttly different and are switched on and off in a pseudo-random sequence with currentas I measure it rapidly moving up and down. I was not too interested in the efficiency, just looking for a yellowish red flickering glow out of the eyes nose and mouth of the pumpkin. I have a 10,000, 12,000 and 35,000 millicandela (MCD) LED wired to each pin and more than one pin may be "on" or "off" at one time. MY understanding is that mcd can not be used in a comparison with spherical candlepower (MSCP) which is commonly used to measure brightness of incandescent bulbs. LED luminous intensity is proportional to the amount of current being used but as I mentioned above current is a tough one to nail down.

For me it is sufficient to say that the battery don't drop below six volts if it left on all night and it is bright enough to make people smile which is likewise a desirable outcome and sufficient in itself.

 

[ANTlabs]

You could make a circuit where whenever someone passes by.

 

[BrownOut]

You could make a circuit where whenever someone passes by.

It does what?

 

[giftiger_wunsch]

You could wire it up to a doomsday device?

 

[ANTlabs]

Sorry Brownout, I didn't compleet my sentence. whenever you walk by it turns on.

 

[HarveyH42]

PIR Motion detectors, like on security lights are pretty cheap these days, not real tough to modify, kind of gets involved if you want to build your own.

IR receiver modules are also pretty cheap and easy to use. You can probable salvage one, most things use a remote these days. Plenty of examples of how to build a 38khz transmitter using a 555 timer. The output of the module goes low, while receiving, so it will go high, and trigger what ever you want, when the path is blocked.