Red blinking LED fades in

[overout]

This project is to make a bookmark (a physical one, for a physical book).

My husband gets distracted and forgets where he put down that book he was just reading. So, he and I decided a blinking bookmark might help.

So, I put together a red blinking LED (this LED has a red lens--its not one of the special, clear LEDs that emits red), a 100 ohm resistor, a clicky switch, and a 3V coin-cell battery. The red LED has a Vf of 2V and requires (according to the data sheet) 10mA.

The LED turned on immediately and blinked for 2 hours which seemed good. Then the weird behavior started: I turned off the circuit and came back 4 or so hours later: the circuit didn't seem to turn on, but then I noticed that the LED was slowly fading up. The LED achieved a good brightness and started blinking, but seemed to drain the battery within 10 minutes. I turned everything off for an hour. I turned everything on again and got the same fading-in then power-drain behavior.

Does anyone have a clue about what is going on?

Thank you.

[zener]

This is a self blinking LED?

[modeller]

It sounds like it could very well be a faulty battery, but you didn't say if you tried another one. You could also hook it up to a stand-alone PS ...

[overout]

Yes, this is a self-blinking LED.

I'll try another battery. Thanks.

[zener]

The self blinking ones are fairly unusual in my experience. I had one many years ago and it was very inefficient. You might only get a few hours out of a coin cell, and once the battery is weak it could act as you describe. There used to be a LED flasher IC called LM3909 that did a good job but it is discontinued. You could design a circuit that would let the battery last longer, but it would use more parts and might be a little tricky to make into a book mark.

[overout]

The self blinking ones are fairly unusual in my experience.

This is good to know. Thank you so much.

[adafruit_support_mike]

This would be a good place to use a 555 tmer.

The original 555 (designed in the 1970s) was fairly power-hungry, but the versions made with modern techniques, like the TS555 ( http://www.mouser.com/ProductDetail/STM ... nJYt74Y%3d ) work well for low-power battery circuits. The link goes to a part that costs about a quarter.

The 555 has a long 'engineering history', so there are hundreds of references showing circuits that work for a wide variety of applications. The datasheet for the part linked (http://www.mouser.com/ds/2/389/CD00000893-13244.pdf) shows how to make a simple high/low oscillator that will blink an LED.

The 555 uses two resistors to control timing, so you can adjust the relative sizes of the ON and OFF pulses. For the best battery life, make the ON pulses about 1 millisecond long and the OFF pulses 1or 2 seconds long. Don't worry about such short pulses being hard to see.. a milisecond's worth of light from an LED is several thousand times larger than the human eye's 'bright enough to see' limit.

[tldr]

use a white led. http://www.evilmadscientist.com/2009/so ... -throwies/