Monthly Science: CR2023 Lithium Cells vs. Wearable LEDs

Those wearable LEDs spent the last five months sitting on the kitchen window sash, quietly discharging their CR2032 lithium cells:

Wearable LED with CR2023 cell

Wearable LED with CR2023 cell

Occasional voltage measurements produced an interesting graph:

CR2032 vs Wearable LEDs

CR2032 vs Wearable LEDs

CR2023 primary lithium cells start out around 3.3 V, so these were pretty much dead (from their previous lives in dataloggers) when I slipped them into their holders. The LEDs seem to be blue LEDs, with threshold voltages around 3.6 V, with colored phosphors / filters, so they started out dim and got dimmer. The green(-ish) LED obviously fell over a cliff and went dark in late January; I have no way to measure long-term microamp currents, alas.

The reddish LED is still going, mmm, strong.

If you need a rather dim light for a surprisingly long time, these things will do the trick.

I should gimmick up another astable multivibrator to blink one LED.

The original data:

CR2032 vs Wearable LEDs - data

CR2032 vs Wearable LEDs – data

  1. #1 by brianjwp on 2017-05-01 - 08:50

    The security certificate on some of your ADs is expired.

    • #2 by Ed on 2017-05-01 - 09:08

      As it says in the sidebar, any and all advertisements come from WordPress, not me: That’s Not My Problem in many different ways.

      At the risk of my penny-per-hour revenue, I highly recommend using an ad blocker. [grin]

  2. #3 by madbodger on 2017-05-01 - 09:37

    It used to be, you could flash a neon bulb with a “dead” photoflash or radio B battery for many months, even years. Then technology marched on, and the LM3909 chip came out, which let you flash an LED with a “dead” 1.5V cell for months. Then the LM3909 was discontinued (it was a somewhat clever chip, probably doing a charge pump style boost operation, like a “joule thief” without an inductor). Now I’m tempted to breadboard an LM3909 type circuit…

    • #4 by RCPete on 2017-05-01 - 11:42

      Somebody did a discrete version; Cute little circuit, done by one of the nicer designers at National’s linear group, Pete Lefferts.

      • #5 by Ed on 2017-05-02 - 13:32

        I am definitely soldering a discrete LM3909 atop a lithium cell holder!

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