How can I replace "Wireless Remote Control Switch" with Raspberry Pi?

Question

I am looking for a solution where I can control a "8 Channel Relay" (Link: http://www.amazon.in/channel-control-optocoupler-ARDUINO-Raspberry/dp/B00YY0SYFU?tag=googinhydr18418-21) wirelessly by using raspberry pi. Presently I am using it (8 Channel Relay) by connecting it to GPIO pins (wired connection). I have found, I can use nRF24L01 (Link: http://www.nordicsemi.com/eng/Products/2.4GHz-RF/nRF24L01) but again the problem is relay requires an external power source. Is there any multi channel relay available, which doesn't require any external power source and just can be connected to nRF24L01.

OR

In "4 Channel DC 12V AC 240V RF Wireless Remote Control Switch Relay Transmitter 4CH" (Link: http://www.ebay.in/itm/4-Channel-DC-12V-AC-240V-RF-Wireless-Remote-Control-Switch-Relay-Transmitter-4CH-/121104193817) can I replace the wireless remote control by using nRF24L01 (Wireless Transceiver) to send signals from raspberry pi? Because it is already available in market which doesn't require any external power source.

Thank You!

Answer 1

The "4 Channel Wireless Remote Control Switch Relay" uses the 433Mhz RF frequency (basically the frequency used by garage door openers). The nRF24L01 uses the 2.4Ghz WiFi range. These two products don't work together as is. To make them work, you basically have 2 options:

1. You do not use the nRF24L01 transceiver but instead buy a 433Mhz transmitter, such as this one. You would need to look for a library to control it, or write something yourself.

2. You can break open the 4-button remote you receive with the relay, check the voltage that goes through the 4 buttons (hopefully it is something like 3V3), remove the buttons, solder a wire onto remote at the output end of each button, and connect those wires to your rPi. Then it's the same as in option 1.

I thought about suggesting to replace the 433Mhz receiver module with a 2.4Ghz transceiver. From the looks of it, the 433Mhz receiver module used in that relay is exactly this one. You could desolder this module and replace it with a 2.4Ghz WiFi receiver/transceiver - BUT this would likely not work, as the relay has firmware that knows how to communicate with the 433Mhz receiver, but not with the 2.4Ghz WiFi receiver. So it is extremely unlikely that option would work.

Answer 2

I am using the same wireless remote control switch and have built a program, that sends control signals from a PC. To use it as-is, you would need an 433MHz transmitter (see Phil's answer) and an ATMega8 controller with a USB plug hooked to it (I have repurposed an USBASP programmer so I don't have to solder anything). Install avr-gcc, build the firmware, flash it into ATMega8, then connect transmitters data pin to port PB3 (don't forget to supply power to the transmitter). The commandline/ directory contains a program, that communicates with the controller and asks it to send a specific signal - you need a binary 24-digit code like 111000100100001001100000.

It seems, that last 9 digits is the command for the relay. For example, "110000000" turns off the one-channel relay, and "001100000" turns it on.

As you already have a Raspberry Pi, you can skip the ATMega8 part and change the program to run on Raspberry itself. However, there are two advantages running the code on a separate controller:

• you can attach an usb-enabled controller not just to a Raspberry Pi, but also to any Linux computer (for example you would possibly try out sending different codes using a PC);
• 433MHz works better on higher voltages (you can supply up to 12V); Raspberry PI GPIO voltage is 3.3V, ATMega8 can run on 5V. When I tried running the transmitter on 3.3V, I got a very limited range - about 55cm. Switching to 5V boosts the range to a few meters. However, you can use a transistor with a Raspberry Pi to translate 3.3V signal level to a higher voltage.

GitHub: http://github.com/kmeaw/afb422

You need to checkout branch "pt2262" - it should work with your device.