Simple indicator with same principe that e-paper ? (bargraph or dot) - Page 1
Forum section: electronics / beginners

author: JL34
author_rank: Contributor
timestamp: June 03, 2022, 08:13:35 pm
content: Hello,I try to find a low power and low cost display to indicate a simple level on an outdoor sensor (low, medium, high level for example). This level will only be refreshed at MCU wake-up, each 5 minutes. So ideally, the indicator should not consume power when MCU is sleeping. So I have though to an e-paper bargraph (or dots to realize a bargraph). But I have not found one.Does someone know a type of indicator that could correspond to my needs, or have an idea to realize a solution ?Thanks

author: ataradov
author_rank: Super Contributor
timestamp: June 03, 2022, 08:55:48 pm
content: Here is a simple 5-dot e-ink displayhttps://www.digikey.com/en/products/detail/e-ink-corporation/SCD722002/7380338

author: JL34
author_rank: Contributor
timestamp: June 03, 2022, 09:52:20 pm
content: Thanks @ataradovBut as the sensor I am designing aim to be low cost, this one is a bit pricey. Specially here in Europe with taxes...

author: ataradov
author_rank: Super Contributor
timestamp: June 03, 2022, 10:23:38 pm
content: Well, all e-ink products are not cheap. If you need something cheaper, then you need to look at LCDs. There are bar-graph LCDs that are reasonably cheap, but they would need minimal amount of power to operate.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 03, 2022, 11:16:36 pm
content: Flipdot?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 03, 2022, 11:25:10 pm
content: A static drive LCD is probably your best bet- think how long a basic digital watch runs on a small lithium coin cell.The other advantage of an active display is that you know when the battery is dead - with a e-ink etc. you don't know if the reading is valid, or is just the last one before the battery died.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 04, 2022, 02:36:01 am
content: Quote from: JL34 on June 03, 2022, 09:52:20 pmThat's going to be about 5 euros with taxes in low quantities? If that's too expensive, e-ink displays are not for you, I'm afraid. I looked on Aliexpress as well and was unable to find something cheaper than this.I don't know for sure your power budget in "sleep" mode, but if cost is an issue, you should probably just use a regular LCD display. Small ones with just a few segments draw very little power. Like that for instance:https://www.excel-display.com/bargraph.shtml

author: JL34
author_rank: Contributor
timestamp: June 04, 2022, 07:33:35 am
content: Thanks for your replies.Quote from: mikeselectricstuff on June 03, 2022, 11:25:10 pmInteresting words. I have forgotten that LCDs could consume so low power. I will take a look at this display type, and flipdot too. For this one, I believed it exists only for sport score display...My whole design consumes 1-2uA at sleep. I hope a could find a display with same magnitude consumption.

author: mariush
author_rank: Super Contributor
timestamp: June 04, 2022, 08:14:25 am
content: For a basic 3 state indicator, if the design allows maybe you should consider just having 3 leds and maybe a push button.Hold the button down and the state led lights up.Or, without a button, just flash the led for a few ms every 5 seconds or so.You can get red leds that are super bright even with less than half a mA and with a CR2032 battery it would probably blink for a yearIt will be more power consumption but cheaper than adding driving LCD complexity, the lcd itself, maybe the zebra strip material to connect lcd to pcb.If you do get lcd, you should look at mass produced ones like the 4 digit used in watches or 8 digit ones used in the cheap 1$ multimeters and pocket calculators.

author: ledtester
author_rank: Super Contributor
timestamp: June 04, 2022, 09:35:25 am
content: Quote from: JL34 on June 03, 2022, 08:13:35 pmIf this is just a hobby project, how about repurposing a solar powered calculator or any other coin-cell powered calculator? Could be a low-power way of driving an LCD display without involving your MCU. Hook up GPIOs to the key pads to operate the calculator and change the display.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 04, 2022, 09:38:27 am
content: There are indicators that are based on a tube with some "stuff" in it, and which can indicate a level, and they look somewhat like the glass thermometers. The level is changed by running a DC current though it for some time. I have never seen these myself, but apparently these have been used for for hour counters. I also don't know what these things cost, or even if they are still available.

author: Gyro
author_rank: Super Contributor
timestamp: June 04, 2022, 10:10:42 am
content: Quote from: Doctorandus_P on June 04, 2022, 09:38:27 amMercury column elapsed time indicators. They can only take a very small current and move very slowly (10s on hours full scale being about the fastest at several mA). They are very good as... elapsed time indicators. No use as status indicators though.Edit: 85uA max for 100 hours (min) full scale, datasheet attached...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 04, 2022, 10:38:44 am
content: One of these tiny LCDs maybe ?Not static drive, though you might be able to get 3 unique patterns with non-multiplexed drive

author: Gyro
author_rank: Super Contributor
timestamp: June 04, 2022, 11:10:29 am
content: Yes, a smallest possible non-muxed LCD, driven by a couple (maybe one) of 74HC86 XORs, with one or two gates used as a simple inverter oscillator at lowest possible drive frequency. I'd be surprised if it took more than a few uA.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 04, 2022, 11:49:26 am
content: Small stepper motors can be quite cheap. You could combine that with a disk with info on it. You can drive it against an endstop in one direction, and then rotate it a fixed amount. (Rotating it does take a relativey big amount of current though.A Motorized potentiometer is also an option. Your uC reads the potentiometer wiper value, and only rotates it if needed. But these things are not very cheap usually.