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First time poster. I’m wondering if you can help. I am trying to make a dumb sauna controller (see pic) smart, so as to be able to turn on my sauna remotely. I am very much an amateur. So be kind.

To do this I have wired one of those sonoff relays in parallel to the push button switch that toggles in on/off. I use about 2 meters of flex heat proof (link below) behind the sauna cladding to my Sonoff switch at ground level (where it’s cooler). The switch is connected directly in a NO setup with the Sonoff and works well. However, when the sauna heats to about 70 degrees the controller will turn off on its own. (Controller is higher up where it gets hot) If I turn it on again, it will stay on but turn off again after around 10 minutes. If I disconnect the flex (at the controller) and so make it dumb again, it works as normal at high temps. If I disconnect at the sonoff switch but leave the 2 meter of cable connected at controller it turns off by itself, just as it does when connected to the sonoff. So I’ve ruled out the relay. The controller gives 3VDC when I put a voltmeter on it at the controller button but after the cable span it’s only 2VDC. Just before it turns off it drops to 1VDC. However, the relay doesn’t close.

My suspicion is my length of cable and heat are combining in some way, or perhaps the type of cable, 2 meters is probably too much. I’ve reduced cable length as much as I can. Could it be that the controller, at high temps can not provide power to that length of cable? Any help or guidance very much appreciated.

Thanks for your time.

PsmGoods 32 Feet 22 Gauge Silicone Wire Super Flexible Silicone Rubber Wire Cable 22 AWG Silicone Wire 16 Feet Red/16 Feet Black (22 Gauge) https://www.amazon.co.uk/dp/B07428WN78/ref=cm_sw_r_cp_api_mWC8Bb7QJWDEK

Sonoff Smart Remote Control Wireless Switch Universal Module 4ch DC 5V 12V 32V Wifi Switch Timer Phone APP Remote Control Support Alexa Voice Control for Smart Home https://www.amazon.co.uk/dp/B07DS44LXJ/ref=cm_sw_r_cp_api_ISC8Bb1D5KN05

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  • \$\begingroup\$ picking up noise on the cable, and causes the button to trigger. Does the same button that you are controlling affect both on and off functions? \$\endgroup\$ – Passerby Nov 19 '18 at 22:37
  • \$\begingroup\$ Yes Sam the Sonoff is isolated, independently powered. You are correct, it’s not powering ‘a switch’. I mean is he controller able to ‘power’ that cable length. Or is there a limit. I’m dealing with 3VDC...... @Passerby Yes, same button for on and off. Yet controller never turns on, only off, and only when controller is at high temps (70ish). But when manually turned back on it will take a while to turn off again... Note The sonoff relay is setup to connect for 500ms and then disconnect, to simulate button press. \$\endgroup\$ – Curious J Nov 19 '18 at 23:19
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    \$\begingroup\$ The options here are use a relay closer to the button, or use an alternative like an optocoupler. Power the opto from the dc input of the sonos, with the opto inside the case. \$\endgroup\$ – Passerby Nov 20 '18 at 0:46
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    \$\begingroup\$ Something like a miniature relay, maybe this reed relay would fit inside the case. It would prevent the long wire from being connected directly to the controller. The relay is unlikely to trip based on noise alone. mouser.com/ProductDetail/Hamlin-Littelfuse/… \$\endgroup\$ – Passerby Nov 20 '18 at 0:52
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    \$\begingroup\$ @Passerby I owe you a drink. 2nd Miniature relay (12VDC NO) arrived today (first didn’t work). Set it up, fitted it neatly inside controller and boom, works like a charm. Had a Sauna this evening, it was up to 90 degrees. No random turn offs. Delighted. Thanks for your help. \$\endgroup\$ – Curious J Dec 7 '18 at 22:15
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Educated guess is that the length of wire used is causing a floating condition, and picking up noise. This is causing signal to change, triggering a false button press. Essentially wires acting like an antenna. There are a few ways to fix this electronically, like using shielded cable or twisted cable, using an optocoupler locally ( that might still have some issues with noise), a filtering circuit, etc.

A better option is a mechanical relay. A relay will be less likely to trigger based on noise due to its current and voltage requirements on its solenoid section. It can still be triggered remotely, even at a couple of meters without issue. Since the switched side will be right on the target board, the button will not experience noise. Based on OPs response this has solved their issue.

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