Posted: 2/20/2026 6:14:42 PM EDT
[Last Edit: Bophades][Edited]
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I need a super low power relay controller so my HomeAssistant can wifi-control a garage door opener. So im thinking ESP8266 for as low draw as possible. This kit on amazon seems to be what I need, right? I need it to be super low power so that it can be controlled from the 2 wire cable from the garage door unit to the button on the wall. Now, its gonna get weird here, so this just may not work lol. 1. The line the device gets powered from (V-in and Gnd) will also be the line that gets temporarily shorted (separate relay Gnd and the NO) to activate the garage door unit. 2. The line from the garage door is 3.8Vdc so yeah a bit too hot for a 3V3, but in this case V-in wants 5v anyways, will the V-in be OK with 3.8vdc instead? 3. Assuming #1 there ends up not being a problem, i guess its possible that my arduino unit may crash out and reboot everytime I use it to open/close the garage door. 4. If I buy that kit, how do I program it? Am I supposed to buy some extra head kit or something that has USB? ETA: corrected link to appropriate device |
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That kit is just a relay. There is no MCU. You'll have to add one. Could be a number of things: Arduinos, ESP8266, ESP32, Raspberry Pi, Adafruit Trinket. There are a lot of options. Here's a version that actually includes a microcontroller: https://www.amazon.com/Acxico-ESP8266-ESP-01S-Module-Control/dp/B08PB6Q2JF You program them using the Arduino IDE and you'll typically use a USB UART of some kind. I have no idea what you need for the kits above because there's just not enough accurate info in the Amazon pages. ESP8266 is pretty outdated. The ESP32 is the replacement and is much more capable...which probably doesn't matter much here. Personally I like Adafruit Trinkets for this kind of stuff. The Adafruit ecosystem is typically very well documented and organized...just gotta hold your nose and ignore all the political BS in their site. |
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got it ok thanks. ok so id need something like this to program it I believe. these controllers seem to want 5V which tells me its got built in regulation right? since isnt the normal ESP controller a 3V3? so im hoping that the regulartor can deal with my 3.8v input being 1.2v below what it expects. as well as those other issues I identified that may come up. |
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Originally Posted By Bophades: I need a super low power relay controller so my HomeAssistant can wifi-control a garage door opener. So im thinking ESP8266 for as low draw as possible. This kit on amazon seems to be what I need, right? I need it to be super low power so that it can be controlled from the 2 wire cable from the garage door unit to the button on the wall. Now, its gonna get weird here, so this just may not work lol. 1. The line the device gets powered from (V-in and Gnd) will also be the line that gets temporarily shorted (separate relay Gnd and the NO) to activate the garage door unit. 2. The line from the garage door is 3.8Vdc so yeah a bit too hot for a 3V3, but in this case V-in wants 5v anyways, will the V-in be OK with 3.8vdc instead? 3. Assuming #1 there ends up not being a problem, i guess its possible that my arduino unit may crash out and reboot everytime I use it to open/close the garage door. 4. If I buy that kit, how do I program it? Am I supposed to buy some extra head kit or something that has USB? ETA: corrected link to appropriate device Put a diode/rectifier in the garage door line, and then connect that to a 3-cell battery holder with NiCd batteries (NiCd can be floated and 3 cells will run from 3.0V to 4.5V so any voltage in that range will be OK.) Connect the arduino to the batteries, both of which are connected after the diode. Connect the relay to short out the lines before the diode. During the time it's shorted, the diode will prevent current from batteries flowing back into the short, and continue to power the arduino. One it opens it'll go back to float charging. Most arduinos can be programmed via a serial port, so you need a USB to serial converter to program. You can optionally use a AVR RISP clone, but using the serial bootloader is going to be far easier. ETA: Per Targetwork's excellent comment below, you probably want to see how much current can be sourced from the line, and also realize that the NiCds will need to be charged first or just charging them will result in it looking like a stuck button. |
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1. The line the device gets powered from (V-in and Gnd) will also be the line that gets temporarily shorted (separate relay Gnd and the NO) to activate the garage door unit. 2. The line from the garage door is 3.8Vdc so yeah a bit too hot for a 3V3, but in this case V-in wants 5v anyways, will the V-in be OK with 3.8vdc instead? If I'm correctly interpreting that to mean that there's a 2-wire cable from the garage door controller to a momentary pushbutton switch on the wall that you briefly press to actuate the garage door controller to open or close the garage door, then I'd advise against trying to use that to power the microcontroller, for a number of reasons. First, if that switch shunts the 3.8 VDC to ground, then there almost certainly is a high-value resistor inline with that, which means that you're unlikely to be able to draw enough current to power the microcontroller. But also, having the microcontroller activate a relay to short out the power supply to the microcontroller (to mimic a human user activating the pushbutton), IMHO that's a poor way to engineer a circuit. Is there no other way to power the microcontroller? How about maybe (slowly) charging a supercapacitor or battery from that 3.8 VDC, but isolating that power circuitry from the 3.8 VDC line with a schottky diode such that shorting that 3.8 VDC line to ground doesn't actually short out the power supply to the microcontroller? Maybe a diagram of what you're trying to do would help, though. |
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Originally Posted By targetworks: 1. The line the device gets powered from (V-in and Gnd) will also be the line that gets temporarily shorted (separate relay Gnd and the NO) to activate the garage door unit. 2. The line from the garage door is 3.8Vdc so yeah a bit too hot for a 3V3, but in this case V-in wants 5v anyways, will the V-in be OK with 3.8vdc instead? If I'm correctly interpreting that to mean that there's a 2-wire cable from the garage door controller to a momentary pushbutton switch on the wall that you briefly press to actuate the garage door controller to open or close the garage door, then I'd advise against trying to use that to power the microcontroller, for a number of reasons. First, if that switch shunts the 3.8 VDC to ground, then there almost certainly is a high-value resistor inline with that, which means that you're unlikely to be able to draw enough current to power the microcontroller. But also, having the microcontroller activate a relay to short out the power supply to the microcontroller (to mimic a human user activating the pushbutton), IMHO that's a poor way to engineer a circuit. Is there no other way to power the microcontroller? How about maybe (slowly) charging a supercapacitor or battery from that 3.8 VDC, but isolating that power circuitry from the 3.8 VDC line with a schottky diode such that shorting that 3.8 VDC line to ground doesn't actually short out the power supply to the microcontroller? Maybe a diagram of what you're trying to do would help, though. no diagram needed, you nailed it perfectly what I was thinking there. ahhh ok all thanks for all this. so now Im considering another possible option. I was going to have to buy a 2nd controller anyways, for IR and a 433mhz transmitter for inside the home devices. so maybe just get a single ESP32, and get a IR txcvr, an RF433MHZ txcvr, and the relay. and this time, just sacrifice the tiny little board of one of the garage door openers I have and connect the relay to that. will also have to figure out a 5v-to-3v for the garage door opener, or just continue to use the CR2032 button battery. this way its just 1 controller I have to deal with |
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