Wall switch to send rf signal

Thread Starter

Fbcircus

Joined Jan 10, 2021
4
Hi there,
I would like to have my wall switch to send a short rf signal when either turning on or off.

I believe what I am looking for is a 220v to 5v acdc, followed by a edge detector (both when transitioning from off to on and vice versa), followed by a rf transmitter activated by the pulses generated by the edge detector.
Can anyone recommend an easy way to achieve this? I cannot be the first person needing this :D
Thank you!
 

MisterBill2

Joined Jan 23, 2018
9,310
The question is not clear. I am guessing that at every change of state in a switch in a 220 volts lighting system the TS wants to output a burst of RF. If all bursts are to be the same then only an on/off controller is needed for a single transmitter. If that iis correct then here is the method:
Start with a small 220 volts AC coil DPDT relayOne set of contacts connects a capacitor to charge whikle tghe relay is energised, and connects the charged capacitor to the RF generator through a diode when the relay de-energises. The second set of contacts connects another similar capacitor to charge while the relay is not energised, and connects the capacitor to power the RF source through a diode when the relay energises. The charging voltage and capacitor values will be determined by the power requirements of the RF module and how long the pulse needs to be. The pulses do not need to be the same length.
Certainly there are more complex ways available but this scheme is simple and reliable and quite low cost.
 

sghioto

Joined Dec 31, 2017
2,395
Or better use the relay contacts to switch a 555. This will give definitive ON-OFF switching.
The component values listed give a 1 second duration.1610311548962.png
 

sghioto

Joined Dec 31, 2017
2,395
How will the Shelly 1 unit activate the RF module when the light switch is turned OFF?
If the button is held down on the RF module won't that send a continuous signal?
 

Thread Starter

Fbcircus

Joined Jan 10, 2021
4
How will the Shelly 1 unit activate the RF module when the light switch is turned OFF?
If the button is held down on the RF module won't that send a continuous signal?
The shelly 1 can be configured to stay on for a fraction of a second (shelly 2.5 has decimals, I believe shelly 1 will be the same), as about the transition from on to off, the shelly a2.5 can operate in 'edge' mode detecting that transition, but you are right I should verify if shelly 1 does the same before buying it
 

MisterBill2

Joined Jan 23, 2018
9,310
Either of the relay circuits will work, the one I described discharges the capacitors into the RF module, while the one with the Spdt relay uses the capacitor charging to power the module. But the circuit with the SPDT relay places a constant load on the power supply while the circuit that I described only loads the supply to charge the capacitors.. So it is more efficient and does not generate as much heat. Also, it is not limited by tgha maximum current capability of a 555 timer IC.
 
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