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I'm looking for a component that can display a (binary) state without being powered. The only things I could come up with are flip-dots and e-ink. Flip-dots are hard to source and e-ink is expensive. I am aware that LCDs draw very little power, but they still require a driver and a battery. Is there something I'm missing?

Edit: What I'm working on is basically a cartridge with an EEPROM that slots into a device that reads and writes to it. The purpose of the display is to indicate the status of the EEPROM content to the user while disconnected from the receiving device.

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  • \$\begingroup\$ Is it acceptable for it to use power just while changing state? If so, how much power and for how long? \$\endgroup\$
    – Davide Andrea
    Commented Jul 3, 2023 at 22:33
  • \$\begingroup\$ @DavideAndrea Yes of course it can use power while changing state. It can use a few watts if necessary. It just has to retain the state while powered down. \$\endgroup\$
    – Zipdox
    Commented Jul 3, 2023 at 23:24
  • \$\begingroup\$ @glen_geek Yes they need to be rewritable. I updated the post with more details. \$\endgroup\$
    – Zipdox
    Commented Jul 3, 2023 at 23:59

5 Answers 5

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Some time ago I was thinking about this.
Simple solution is to use a small solenoid, no spring return, bidirectional.
You can make your own. It is very simple, just a coil with magnet inside.

The indicator in panel has two notches which allow the springs to hold the indicator in one of the position (indicator in or indicator out) after selenoid pulse disappear.

enter image description here

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Hobby RC servo (eg. SG90) with a 3D-printed indicator flag. Cheap (a couple dollars), runs on 5V to change state and capable of displaying more states than binary if required (eg. 'gas gauge' for a non-volatile memory with 180° pointer motion). Single wire interface to your MCU. Below image from here.

enter image description here

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Years ago I built signs using magnetic flip dots. There is a "U" shaped electro magnet that gets pulsed by current. This flips the magnet which is painted back/yellow. Current only needs to be there for a mS. The dot remains flipped.

enter image description here enter link description here

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    \$\begingroup\$ You most likely mean ms, not mS. \$\endgroup\$
    – Hearth
    Commented Jul 4, 2023 at 16:13
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    \$\begingroup\$ I emailed AlfaZeta and hopefully they'll get back to me with a reasonable price for flip dots. I think I'll go that route. \$\endgroup\$
    – Zipdox
    Commented Jul 4, 2023 at 22:06
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An LCD with a micro power LCD-optimized cpu driving it will have the endurance of the shelf life of the battery that’s powering it. In other words: stick a super capacitor in there and it will be as good as any permanent display unless the device is not used for a decade or so.

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If you want Cheap!:

If the status of the EEPROM is known by the system it connects to it could be indicated to the user when it was removed and the user can set a manual "switch" on the device.

Some devices (eg some camera batteries) have such an indicator.
It is not managed in any way by the system proper - just by the user.
This can be used to indicated charged / used - or for any other purpose that the user may desire.

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