I bought a fake/empty alarm box for my house, but thought I'd make it look more realistic by putting some kind of periodic flashing bulb in the unit.
I made up an astable on stripboard with uneven RC sides, so the thing flashes very briefly every 1-2 seconds. This works fine, but I used an LED, which isn't bright enough to be seen through the blue transparent panel of the alarm box, from any distance at all.
The cct is driven by a 9v battery. Can anybody suggest something I can use for a bright periodic flash?
I bought a fake/empty alarm box for my house, but thought I'd make it look more realistic by putting some kind of periodic flashing bulb in the unit.
I made up an astable on stripboard with uneven RC sides, so the thing flashes very briefly every 1-2 seconds. This works fine, but I used an LED, which isn't bright enough to be seen through the blue transparent panel of the alarm box, from any distance at all.
The cct is driven by a 9v battery. Can anybody suggest something I can use for a bright periodic flash?
I didn't know you could get super bright led's. I'll try them first. Can you get white/clear ones? I can only see red and green at 3000mcd at the moment?
They make blue ones that bright and white ones even brighter. Try Hosfelt Electronics for "hobbyist" quantities. You can get prime grade ones from Nichia in fairly small quantities also - see their website
there are several types and colors of led having the multivib incorporated beware of the front panel, since it might act as a filter thus actually "filtering" the red light out I'd consider bringing the led out of the box by mounting it through the panel....
I thougth about the filtering of the blue front panel, so I decided to find blue LED's I bought some clear/blue 10mm 14,000mcd bombs that I'm hoping to try out this weekend.
Time between flashes = 3.26s Quiescent current @ 9V = 200uA Current required for charging Ct = 12uA Current required for flash = 9uA (Averaged over period) Total power budget = 221uA * 9V = 2mW
For a typical 9V, you could have 1000 or more service hours.
(created by AACircuit v1.28 beta 10/06/04
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You can adjust the length of time of the flash by adjusting the value of Rd. You can adjust the frequency of flashes by changing Rt or Ct.
For a brighter flash, use a smaller value resistor for Ro. That will marginally affect the life. Use a high-brightness LED for best results.
Using a low-leakage capacitor for Ct is probably important for the timing, but it'll be hard to get a 10uF cap that is low leakage. Avoid electrolytic caps if possible.
When I built this and measured it, it was using more like 150uA quiescent. The datasheet said 200uA, though. The timing (using an electrolytic 10uF, 16V) was pretty accurate.
I used the datasheet from STMicroelectroncs for the TS555CN for this design. I ignored discharge pin leakage, which is claimed to be under 100nA.
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Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
I think you left out the pin numbers so I put Pin One in.
10 uF Electrolytics work okay in this circuit, and so do 10 uF tantalums. Using a 10 uF plasti cap is going to be really expensive and it will be huge.
I've built simpler flasher circuits using two transistors and they draw low current if you set them for low duty cycle, like yours below. See URL
Better yet, use a two or three AA cell holder, and run it off 3 or
4.5VDC. The AA cells should last 6 months or more. Here's a good circuit.
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Those are 2N2222 and 2N2904 transistors. Blue LED won't work with 3V, you have to have 4.5V. This should last more than a year with two AA cells. I built one of these and I used a pair of AA cells from a flashlight that were 'dead', and it ran for over 6 months.
If possible, increase the value of any resistor that controls the LED current. Most blue LEDs are nonliear and have efficiency increasing as current is changed towards just a few milliamps - most blue LEDs are noticeably much more than 20% as bright at 4 mA as at 20 mA.
See if the flashing circuit draws much current - I know how to make a flashing circuit that draws a fraction of a milliamp.
Use an LMC555 and a section of a 4049 inverter to drive an LED with 4 mA for a low duty cycle (like .2 second on, .8 second off). Total current draw should be about 1.5 milliamps, which a 9V alkaline battery should be able to provide for about 400 hours or about 2 weeks. Other circuits, such as ones using a "low power" op amp as an oscillator, can improve upon this somewhat. You may get adequate light with just 2 mA or even less of LED current - it may be possible to get the average current draw down to about 1/4 of a milliamp and then battery life of about 2-3 months is possible.
Wow, there's a lot of responses here! Thanks. I'll have to take the time to go through all of them and give them due consideration.
I realised today that when tuning the cct on a breadboard, I varied the capacitor values to arrive at what I wanted. I really should have made the capacitor values as small as possible, and varied the R values.
Using an array of 2400MaH NiMh rechargables may have helped too. Cheers, Mark
Remember that rechargeable cells lose a certain percentage of their charge just sitting there, without any load. So you have to recharge them every few months just to keep them from going flat.
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