LED Flasher circuit for 1 battery theft control.

[gary350]

I don't have much experience with LEDs. I know this circuit works with 100 volts and a NE2 neon light. Will it work with and LED and 1 AA battery?

We are having a theft problem in the neighborhood. I want to put a simple flashing LED in each window it will make a thief sneeking around in the dark think there is a camera or some type of security system in each window.

T=RxC .01uf x 1M = 1 second.

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[Sceadwian]

No it will not work there is no active device. The reason the neon works is because as soon as the capacitor charges up to the neon's conduction voltage it will dump all the caps energy flashing once and then staying off till it's charged up to it's conduction voltage again, the neon tube is acting like an arc timer with the R/C values, no such effect can occur with an LED.

The simplest solution would be to actually buy blinking LED's, they have the blink circuitry built right into them.
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20 bucks for 100 of them.. These will not work on 1.5 volts though you're going to have to use at least two cells.

 

[gary350]

The RED LED is 1.9-2.2v

The BLUE LED is 3.0-3.3v

Security systems always have RED flashing lights. How do I get 2 AA batteries to flash a RED Flashing LED?

2AA batteries = 3 volts

I = 20 ma

E = voltage drop across resistor = 1 volts

R = E/I = 1/.02 = 50 ohms

If I am correct a 50 ohms resistor in series with the LED should work.

 

[Sceadwian]

Use the Red one and a small resistor to compensate for the over voltage a fresh pair of 1.5 volt cells will exhibit.
3.0 volts of two 1.5volt cells is .8 volts over the high limit, the current the LED draws is 20ma. Toss that into a calculator and you'll see that all you need is a 40 ohm resistor in series. Or you could just use two NIMH batteries. That'd be 2.4 volts and only just barely over the allowed voltage.

I'd throw a pair of NiMh's at it and call it a day.

 

[BrownOut]

YOu can make your LED act like a neon bulb by adding a UJT. Look at the UJT relaxation oscillator in this image. You can connect the LED between the UJT and R1.

 

[Mike_2545]

Or, get a Flashing LED...like these

 

[BrownOut]

YOu can make your LED act like a neon bulb by adding a UJT.

I've taken down my PUT oscillator, because I don't think it will work at the voltages specified. Instead, I'm posting a circuit I got form colon55. It works down to 1.5V.

 

[Reloadron]

You can buy a few of these for under $1.70 each. A few resistors and 1.5 volt batteries and you are done. I agree with Sceadwian, just a simple over the counter solution. Thinking you have a Radio Shack down there in Tenn?

Ron

 

[Sceadwian]

Radio Shack will charge you 10 bucks for something like that. The e-bay link I posted is for 100 LED's for 20 bucks... Hard to beat that price, the batteries are going to be more expensive by far.

 

[sheldonstv]

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this circuit ive used for many years for this very purpose started out life as a go/no go tester for optos-if you use hi brightness leds the flash is quite impressive