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Subject: Re: Blinking LED circuit design

Date: 03/23/03 at 2:47 PM
Posted by: Brian Snell
E-mail: bsnall@lara.on.ca
Message Posted:

In Reply to: Blinking LED circuit design posted by Jeremy Hendrix on 03/23/03 at 12:25 PM:

Greetings. National Semiconductor used to make an IC, #LM3909, which will provide a flasher circuit operating right down to a 1.5 v cell. The chip requires only a few extra components to create a circuit such as you require. In case you are wondering how it can drive an LED from 1.5 volts, it charges up a capacitor, then reverses the cap charge, adds it to the 1.5 volts and -- voila, there is a brief 3 volt pulse which flashes the LED with commendable brightness. With a "C" battery, it will flash one LED for over one year.

The "down" side is that National no longer produce the LM3909 (the company is run by accountants -- not electronic enthusiasts). There are a number of warehouses, however, which still seem to be showing it in their stock lists. Take a look at a Digi-Key catalogue. Mine is a few years old so anything there is probably no good. I believe that Holtek also make a similar chip as well. If you do not have access to any older National Linear Data Books, I can scan you the relevant pages and E-Mail them to you.

Let me know.


Brian Snell.

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