Blinking red LED with a coin [button] cell

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cheapNdisgusting
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Blinking red LED with a coin [button] cell

Post by cheapNdisgusting » Sat Oct 14, 2017 6:31 am

Using an "off the shelf" red blinking 5mm LED [3v. 20 ma] and a small current limiting resistor controlled by a tilt switch (very simple so far) but since small size is very important I would like to power this with a coin cell [button cell] or two that are no larger than a quarter [25 cents] and no thicker than 1/4". This will be encased in epoxy so changing the battery is not an option.
The desired end result would operate [on blinking] for 10 to 15 seconds around 4 or 5 times in a 24 hour period and last as long as possible. A year would be perfect.
Coin cells like a CR2477 have a 1000 mAh rating which to a novice like me means that it would operate a 20 ma LED for a long time. I want to make a "PUT THE TOILET SEAT BACK DOWN" reminder to "attempt" to teach my son and keep both of us out of trouble. Seat up - light blinks and seat down it's off.

Am I on the right or wrong track with the battery choice? Does anyone have a better battery choice?

I am open to any and all suggestions and thanks in advance for reading this.
cNd

dyarker
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Re: Blinking red LED with a coin [button] cell

Post by dyarker » Sat Oct 14, 2017 8:57 am

CR2477s are only 3V when brand new and under no load. They are considered "dead" when voltage is down to 2V.

The blinking LEDs I found are 3.5V minimum to 14V maximum. Your circuit with one CR2477 might last a week, if it worked at all.

I suggest two CR2477s in series. That would be 6V new, 4V dead. Recalculate the resistor. Since 4V is greater than 3.5V, and short period at 20mA is a vveerryy light load, it could last a couple years.

Cheers,
Dale Y

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cheapNdisgusting
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Re: Blinking red LED with a coin [button] cell

Post by cheapNdisgusting » Sat Oct 14, 2017 11:11 am

Thank you for your reply. As I mentioned in my original post - there is room for two (stacked) no more than 1/4" high total. I will solder them.
Thanks again.
cNd

dyarker
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Re: Blinking red LED with a coin [button] cell

Post by dyarker » Sat Oct 14, 2017 1:55 pm

To meet thickness limit put the two CR2477s side by side with a wire (or flat metal strip) from bottom of one to the top of the other.

Or stack two CR2330s. They are a touch less than 1/8 inch thick each. How you would solder them together I don't know, because solder does not "wet" the metal batteries are made of. Even top and bottom wires will be a problem. Maybe heat shrink tubing to squeeze together.

Or, Or look for coin cell holders that are 1/4 inch, or less, tall and put side by side. (for either cell type)

I don't see a single cell way to get the 3.5V minimum for blinker.

Cheers,
Dale Y

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Re: Blinking red LED with a coin [button] cell

Post by cheapNdisgusting » Sun Oct 15, 2017 1:02 pm

Thanks again dyarker, since this is still in the "brain-fart stage" the first attempt will probably go into a Tic Tac container [cut down] and filled with epoxy Just in case it falls off. I will hold it on with a double sided sticky tape.
When I get it de-bugged I will post a picture.
Thanks again.
cNd

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Janitor Tzap
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Re: Blinking red LED with a coin [button] cell

Post by Janitor Tzap » Mon Oct 16, 2017 10:51 am

Someone already made one.

http://tipalert.com/


Signed: Janitor Tzap

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cheapNdisgusting
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Re: Blinking red LED with a coin [button] cell

Post by cheapNdisgusting » Mon Oct 16, 2017 12:03 pm

Yes I know - but that one(s) make sounds, don't last very long, and I just want to make it myself. :grin:
cNd

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