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Small Alternating LED Flasher

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Technoboots

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Hi, i'm trying to work out the best way to make a circuit which will flash 2 LED's alternately at quite a quick speed. There are a few requirements though.

1-I need it to be as small as possible since it will need to fit inside a watch casing.
2-It should be able to run off a single 3v button battery.
3-This one is an option, but it would be good if you could press a button and have it flash for 20-30 seconds and then switch off. Alternately holding down a button to keep it activated would be Ok.

I've been reading through the forum and have read about different chips such as the 555 chip. I am guessing something like this would be required. I only have a limited knowledge of electronics, but my younger brother is doing an electronics course so if I get stuck on a few things he can help me. Any help would b appreciated. thanks
 
The minimum supply voltage for an ordinary 555 is 4.5V. So 4 button batteries in series would make it blink 2 LEDs for a couple of minutes before the batteries are dead. A much bigger 9V alkaline battery will last 24 hours.

You need a very low power circuit so you can use weak button battery cells. The circuit must not have the high current LEDs on very long but it must blink each LED for only a few milli-seconds each time.

Discovery Circuits on the web have some low power LED blinking circuits.
 
Thanks for the site, i've looked through and there are a few possibilities. There was 1 chip called lm3909 (I know this chip has been discontinued). I have read that it can run on 1.5v and that it can be used for a single led flasher. Would it be possible to use this chip to make an alternating dual flasher?
 
The smallest LED flasher I can think of would use a PIC10F206. Just a 0.1uf cap and a small resistor (optional at 3V as the PIC has about 50ohms on the output lines)
So blink, sleep (save battery power) repeat.
 
I've looked through google and found a diagram for a low powered astable multivibrator which runs on 1.5v. I am not sure how this would be converted to an alternating flash led.
https://www.electro-tech-online.com/custompdfs/2007/09/1HZOSC1.pdf
This project has to be an alternating flash rather than both flashing at the same time. I have also found out about 'flip flop' circuits, but these run on 9v.
The battery life is something I am not worried about since this will only be used for very short periods.
 
I have an LM3909 blinking an LED for 1 year when it is powered by a huge and heavy alkaline D cell. It also uses a pretty big eletrolytic capacitor.

The watch must be huge to contain a D cell and a big capacitor.
 
Hello

May be off from what you are requiring but while trying to get my head around electronics I decided to take apart a quartz clock movement of 1.5v.

Inside the case of the movement you will find the very small circuit it consists of a watch crystal and all the parts required that makes the clock tick. If you very gently take this out from the housing remembering where the battery connected to the circuit now throw away the case.

You now have the circuit with the electro magnet attached. Gently remove the coil cutting the very fine wires.The coil output can be used to light your led's. You will have to solder wires to the circuit where the battery terminals once touched. solder one wire on each for + and - these can be now connected to a battery of your choise.You will have to solder wires to the circuit where the coil wires were, these can be for the power to the LED's.

The good thing about these circuits is they are bipolar so you can wire the two LED's up to opposite supply with this you will get one led flashing and the the other.

I include a photo but it does not show much detail. In the photo I only have one led but you can use two wired up opposite to give alternating flashes.

Hope this is of use.If you require any more info please ask.

Wombweller
 

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I'm going to be using a button battery for power. Longevity is not an issue for me.
I found plans for a 1.5v astable multi vibrator, but don't know if it could be converted to be a dual alternating LED flasher. I also read about astable 'flip flop' circuits, but these run on 9v.
Wombweller, that sounds interesting, it may be useful. I've never taken a clock apart before, but i'll have to have a look at one.
 
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A red LED needs about 1.8V and other colors need a higher voltage so forget about only a 1.5V battery.
There are many 3V astable oscillator circuits on the web that alternate two LEDs. They use two pretty big electrolytic caoacitors. They have a high average current draw because it doesn't blink. Then a button cell will last only a few minutes.
 
Technoboots said:
I'm going to be using a button battery for power. Longevity is not an issue for me.
I found plans for a 1.5v astable multi vibrator, but don't know if it could be converted to be a dual alternating LED flasher. I also read about astable 'flip flop' circuits, but these run on 9v.
Wombweller, that sounds interesting, it may be useful. I've never taken a clock apart before, but i'll have to have a look at one.


Hello

You will find theirs not very much at all to the circuit and is quite small about 20mm x 10mm The hardest thing is soldering the wire's that replace the coil , the circuits quite fragile and I destroyed three trying ( but i'm not very experienced with soldering) With my demo I wired two led's up in opposite polarity and working from three volts they flashed very happily.

One thing that I also found was while touching the circuit the led's stopped flashing but then started again but they flashed very quickly.I think this was due to static and it effected the frequency of the tiny crystal.

I don't know how small you want to go but this is quite small, don't know what alternative power supply you can use.


Regards wombweller

PS. You can buy many of these quartz clocks on ebay for very little cash and the circuit is already built, it's just a case of is it suitable for your needs
 
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I'm going to be using 2 red LED's and a 3V button battery (cr1220). 20mm by 10mm sounds like it would fit in the case so would probaly work. What type of clock specifically did you use? Do you have a picture of one, it would make it easier for me to find the right type.
 
Technoboots said:
I'm going to be using 2 red LED's and a 3V button battery (cr1220). 20mm by 10mm sounds like it would fit in the case so would probaly work. What type of clock specifically did you use? Do you have a picture of one, it would make it easier for me to find the right type.


Here are the type that I purchased-

**broken link removed**

Item number: 260164062003

But I think many are the same but I am unsure.

wombweller
 
A tiny CR1220 lithium battery cell is rated at 40mAh when it has a 0.064mA load.
It drops to 30mAh when it pulses 2.8mA for only 2 seconds 12 times per day.

An LED is fairly bright at 10ma. The tiny battery is doomed. Try it.
 
Thanks wombweller, i'm going to order some next week and give it a go. I guess it's time for me to get a new soldering iron, the old one we have is knackered. Audioguru, I am going to try it with the button battery first, depending on the performance it gives will make me decide whether or not I need to change the power source.
Thanks for your help, i'll post more info when i've tried it.
 
finally finished the project (for now at least). The circuit works perfectly for my needs and fits in the case ok. There is only one thing which I would like to change on it though. Right now you have to hold the button down to keep it on. I tried looking for an on/off button which I could use so that when you press it once it keeps it on and pressing it again turns it off. Unfortunatly I could'nt find one small enough to fit inside. Does anyone know of one that could work?
Anyway, here is a video of the circuit in action, I managed to get it working on the first try.
https://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=20499919
Thanks again wombweller
 
Technoboots said:
finally finished the project (for now at least). The circuit works perfectly for my needs and fits in the case ok. There is only one thing which I would like to change on it though. Right now you have to hold the button down to keep it on. I tried looking for an on/off button which I could use so that when you press it once it keeps it on and pressing it again turns it off. Unfortunatly I could'nt find one small enough to fit inside. Does anyone know of one that could work?
Anyway, here is a video of the circuit in action, I managed to get it working on the first try.
https://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=20499919
Thanks again wombweller

Hello
What circuit do you finally use? If you used the quatz circuit then a simple on of switch would sufice.

Wombweller
 
I did use the quartz circuit. I need a push on/off button, not a flip switch though. All the ones I saw only stay on when you press them.
 
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