Self-energising push buttons - Page 1
Forum section: electronics / general

author: nali
author_rank: Frequent Contributor
timestamp: January 07, 2023, 08:38:32 pm
content: I've seen these before but my Google-fu is failing me - they have a snap action which zips a magnet past a coil to generate enough power to allow a MCU to fire off a code via a low power RF transmitter.There seems to be a few finished products out there called "wireless pushbutton" and suchlike which are complete with transmitter and thus require a compatible receiver. But I'm really after just the button mechanism as I want to use my own MCU & TX to interface with existing product.Anyone know who makes these, or what terminology they tend to use? Looking for mainstream manufacturers not here today gone tomorrow Aliexpress/ebay/whatever sellers.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 07, 2023, 09:17:45 pm
content: Omron has some commercial offering:https://automation.omron.com/en/us/products/family/A2W

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 08, 2023, 10:02:14 am
content: I'd be interested in finding a proper manufacturer for these, although I'm only a hobbyist myself. Apparently, "kinetic switch" and "self-powering remote control" seem common names for these. There are also piezoelectric ones, but that's a different approach (piezoelectric effect, instead of induction with a coil and a small permanent magnet). Anyway,"kinetic rf switch"seems to yield quite a few hits on the web, including places like ledbulbs.co.uk, which might or might not be a valid UK seller of such stuff –– I not sure as I non-UK hobbyist ––, which leads to brands like "Culina kinetic switches".BigClive investigated some of the eBay ones way back, and indeed it is very difficult to find which ones are fakes and which ones real, so I don't think even eBay/BangGood/AliBaba etc. are reliable sources, even for a hobbyist looking for just one or two units:If you find out which ones are reputable in UK and/or Europe, perhaps sold in reputable local brick-and-mortar stores, do let us know, please.(Here in Finland, it is common for such specialist companies to not sell to private customers, as they only do business-to-business, and because of reasons, I'm not willing to set up a company even just on paper.)

author: nali
author_rank: Frequent Contributor
timestamp: January 08, 2023, 10:27:27 am
content: Quote from: Nominal Animal on January 08, 2023, 10:02:14 amThanks, "kinetic switch" was an obvious one I hadn't tried. A quick search findsthisbut it's not quite what I was hoping for which is basically a switch assembly with coil(piezo) connections instead of switch contacts and would need to be rugged & waterproof to be used out on the street. I need to emulate an existing 433MHz fob which is why I don't want one with an integrated TX.I'm not even sure such a thing exists but it's something a client asked me about so I said I'd do a bit of looking.

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 08, 2023, 11:03:46 am
content: Quote from: nali on January 08, 2023, 10:27:27 amCan you determine the chip used in the fob? They are often standardized (see above videos), so if it happens to be one of the well-documented 433MHz transmitter chips, it might be a simple case of using a compatible one and just programming the same code.

author: nali
author_rank: Frequent Contributor
timestamp: January 08, 2023, 11:19:00 am
content: Quote from: Nominal Animal on January 08, 2023, 11:03:46 amThat side of things is no problem, the fob, receiver and OTA protocol are our own product which has been in the field for years. So if I can find something it should just be an exercise in energy harvesting and re-purposing the existing fob design.

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 08, 2023, 01:05:39 pm
content: Quote from: nali on January 08, 2023, 11:19:00 amAssuming your hardware and software is suitable for minimal-energy implementation. For example, the chips mentioned in the above videos are designed for the purpose, and simply send a 24-bit value. If yours requires more energy, or the delay from energization to sending the signal is too long (so humans get frustrated by the delay), welp, you're screwed.How about you obtain some of the existing switches, and replace their logic with a carefully measured load ballast, and measure how much power they generate? And then measure exactly how much energy does your existing fob require to send a single key/message. That would at least tell you whether you're in the ballpark, physically, or if you need to add a small wind-up generator above the button with a note telling users to give it a few turns to generate enough enery for sending the RF packet.Otherwise, I'd say you're in the mechanical design realm, and need to find out how to make a physical magnet-and-coil assembly that 1) is weatherproof, and 2) generates enough energy (long enough button travel but still be within weak human keypress force range) to power your existing circuits. Some kind of spring-assisted lever mechanism is probably needed, since humans tend to not push buttons more than a couple of millimeters maximum, and some (elderly) tend to press them quite slowly (gently).

author: nali
author_rank: Frequent Contributor
timestamp: January 08, 2023, 05:32:05 pm
content: Oh I know the fob is energy-conscious; It's not a standard press-to-do-something type, rather it transmits a code every second until you turn it off and runs off a single CR2032. I can't remember how much continuous operation one would get from a single cell (it's not my design) but it's some weeks IIRC.Definately don't have enough MechEng ability to create my own... so if we find something then nice otherwise it's not the end of the world.

author: nali
author_rank: Frequent Contributor
timestamp: January 09, 2023, 09:54:45 pm
content: Quote from: Nominal Animal on January 08, 2023, 10:02:14 amSo I found this one, which is a BLE version and apparently gets enough juice to send out a bunch of Eddystone advertising frames.https://uk.farnell.com/on-semiconductor/ble-switch001-gevb/eval-board-energy-harvesting-ble/dp/3010438.Interesting but not quite what I was envisioning. Anyway as I'm busy with projects at the moment I'm not going to waste time on an idle query - but still might order a couple of decent rare earth magnets & some wire, dust off the 3D printer and have a tinker some day for the heck of it...

author: thm_w
author_rank: Super Contributor
timestamp: January 09, 2023, 10:11:34 pm
content: If the device lasts weeks on a CR2032 then I wouldn't expect it to do well on energy harvesting, that is a large amount of power.Or are you saying, it only lasts weeks because it gets turned on and forget to be turned off?

author: nali
author_rank: Frequent Contributor
timestamp: January 09, 2023, 10:18:57 pm
content: Quote from: thm_w on January 09, 2023, 10:11:34 pmYes. this...The original design is maybe 15yrs old & uses a ATTINY. I'd obviously use a more modern nano power MCU for harvested energy.

author: thm_w
author_rank: Super Contributor
timestamp: January 10, 2023, 12:49:24 am
content: The ATTINY should be OK lasting years on a CR2032, modern MCU may be slightly better.I would work on the code and stick with CR2032. Or maybe a rechargeable CR2032 equivalent and a small solar cell.

author: Halcyon
author_rank: Unknown
timestamp: January 19, 2023, 11:35:29 pm
content: Quote from: Mark Ruiz on January 19, 2023, 09:39:22 pmHmmm... Bot much?

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 19, 2023, 11:38:16 pm
content: Quote from: Halcyon on January 19, 2023, 11:35:29 pmYou're right. I was worried that someone even more newbie in electronics than I am would mistakenly believe that we're talking about reed switches here.We're not; the switches discussed here harvest the energy from the button push to power the circuit itself for a very short moment, just enough to transmit a RF signal packet.

author: Halcyon
author_rank: Unknown
timestamp: January 20, 2023, 12:07:41 am
content: Will flag the account for future scrutiny. The IP address comes back to a VPN service (to no surprise).

author: vk6zgo
author_rank: Super Contributor
timestamp: January 20, 2023, 01:47:46 am
content: Quote from: Nominal Animal on January 19, 2023, 11:38:16 pmSeems like a seriously dumb idea to me--why not the CR2032 & a momentary switch, which only supplies power during its "On" time.

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 20, 2023, 02:11:09 am
content: Quote from: vk6zgo on January 20, 2023, 01:47:46 amThe switches are commercially available, and have been demonstrated to work well. So, why do you say it is a dumb idea?I can imagine many scenarios where the lack of a replaceable battery would be a plus, especially if I had say a dozen of the switches. Replacing the CR2032 is a maintenance task that may be nontrivial; consider for example inset buttons with only the button head protruding. One has to have CR2032 in stock, too.Wireless doorbell push buttons, for example. If I ever find a cheap outdoors one that can handle -45° to +35°C, I'll immediately have use for one.

author: PlainName
author_rank: Super Contributor
timestamp: January 20, 2023, 01:31:55 pm
content: My office doorbell uses one of these. It's just one of many available onAmazon. Feel is slightly squishier than a battery or externally supplied one, but not enough to make you think it's broken. Been stuck in the full force of English weather for four years with zero issues, where my previous ones were forever running the battery flat or otherwise succumbing to early care home syndrome.