Small wireless button -- kinetic (no battery)? - Page 1
Forum section: electronics / projects

author: ebastler
author_rank: Super Contributor
timestamp: October 23, 2024, 06:07:48 am
content: Wireless light switches are available which don't need a power supply, because they generate a short burst of power from the switch actuation itself. (Not sure whether they use piezo or electromagnetic transducers, or something else?) These are often described as "kinetic" wireless switches.For a project I'm currently sketching out, it would be ideal to have a smaller pushbutton -- say 1 cm diameter and up to 3..4 cm in length -- which does the same. An extra little circuit board with the transmitter would be fine, as long as it can be positioned freely vs. the button itself, with a short wire connection. Has anyone come across such a solution? It would need to be off-the-shelf and reasonably robust, since it is meant to be used in a museum exhibit. But it does not have to be weatherproof.As a fallback, is there a micro-power solution you would recommend? A battery-powered transmitter which only gets powered for a short burst when someone presses the button?In either case, power requirements on thereceiverend are not critical; the receiver can be listening continuously. The required transmission distance is about 1 meter. Cycle time between button presses can be a couple of seconds if there should be an internal recovery/recharge time, but 1 second or less would be preferred. Thanks in advance for your ideas!

author: bookaboo
author_rank: Frequent Contributor
timestamp: October 23, 2024, 11:21:26 am
content: If you can tolerate a coin cell this is pretty easy, ESP32-S3 has deepsleep <~10uA, nRF devices <~2uA, TI CCxxxx <~2uAOr the button as a switch to power the entire circuit, so you could use any small RF chip / board that you like with 0uA standby.I did a few keyfob devices like this 20 years ago, the 2 I kept here are still working.

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 23, 2024, 12:14:25 pm
content: BigClive did a couple of videos on these a few years back:The PCB these use, if acceptable size and form factor, might be suitable to your needs, and can easily be found at eBay and Aliexpress. (I found the Germa 433MHz push-button waterproof one interesting, but obviously don't know if it actually is kinetic or waterproof.)

author: nali
author_rank: Frequent Contributor
timestamp: October 23, 2024, 12:26:11 pm
content: I went through this a little while ago, but I had constraints on that it needed to work with a field population of legacy receivers, so kinetic solutions just couldn't provide the power budget.In the end I used an AVR. Battery supply is switched by a load switch IC, enabled by the button and latched by a GPIO. The AVR does its stuff, sleeps for a while (to prevent repeat presses) then cuts the power.From power profiling I should get >5 years from a CR2032 with a couple hundred presses per week.I did findhttps://www.iebelong.combut they weren't that interested.Edit: Found an example of power generated per press/release: 330uJhttps://www.farnell.com/datasheets/2736014.pdf

author: ebastler
author_rank: Super Contributor
timestamp: October 23, 2024, 12:39:14 pm
content: Many thanks, gentlemen! Very helpful replies -- both the Big Clive videos and the suggestions and estimates for battery-powered options.I certainly will have room for a battery that should last at least year, even under heavier use from many museum visitors. Would still love a totally maintenance-free version, since the museum staff is bound to forget about the battery and then scratch their heads when communication eventually fails. But who knows whether the kinetic switches themselves will be as reliable as a decent momentary button? I'll take a close look at the Big Clive videos.For the battery-powered, wake-up/transmit/sleep solutions -- what is the radio standard of choice? Does one of the usual suspects (Bluetooth, Zigbee, ...?) have specific advantages when it comes to establishing the connection quickly without much protocol overhead?

author: bookaboo
author_rank: Frequent Contributor
timestamp: October 23, 2024, 03:23:26 pm
content: For a quick pushbutton I'd go for 433/868 sub GHz. BLE or Zigbee would work but it's likely overkill, I've never done a simple "remote" like that.An easy solution would be RFM69HCW HopeRF module (or any similar module) and use the open source Arduino libs and processor of your choice.Or if you are an ESP32 fan, try ESP-NOW protocol for a single chip solution.

author: tszaboo
author_rank: Super Contributor
timestamp: October 23, 2024, 03:35:45 pm
content: Quote from: bookaboo on October 23, 2024, 03:23:26 pmI think ESP is not a good solution for that. Sleep current is quite high and the bloatware to load in the beginning is long.But this all depends on your battery. If you can hide a AA LiSOCL battery in the device, and you get maybe a hundred button presses in a day, you probably get a few years of battery life. It's just, with a Nordic or Silicon labs micro you for sure would get a decade with the right software and protocol.Kinetic energy harvesting is interesting. But if I try to build a device with the harvester sourced from Digikey, and some specific Power management ASIC, might as well place a battery because that's going to be 5x cheaper.

author: TimFox
author_rank: Super Contributor
timestamp: October 23, 2024, 06:11:04 pm
content: The first (or at least early) TV remote control (from Zenith Radio) did not rely on batteries:https://www.theverge.com/23810061/zenith-space-command-remote-control-button-of-the-month