USB Controlled RF Switch

Here is a fairly simple USB controlled RF switch using a Dow Key relay and an Arduino Nano.

Parts List

Dow Key RF Switching Relay, 12 V Coil With TTL Control

Low Power SMA connectors - Dow Key P/N 401-220802A-ROHS, 401-420832A-ROHS or similar.

High Power N connectors - Dow Key P/N 402-220132A-ROHS or similar

Price new is not easily available. Price used on eBay is $20 - $75

Arduino Nano

Price - many available from $3 and up

USB cable

Price - $2 and up

Berg header, Berg connectors and wires to connect the relay to the Nano

From my junk box, Price a few dollars if you can find what you need. You can just wire it directly.

Wires and Powerpole connector to provide 12V to the relay

On Hand for me, Powerpoles are about $1 in multipacks from Powewerx or HRO

Build Instructions

Connect Gnd on the Nano to Gnd on the relay

Connect Digital I/O 2 on the Nano to TTL Control A on the relay

Connect Digital I/O 3 on the Nano to TTL Control B on the relay

Connect USB cable to the Nano

Here are the Nano connections

Connect 12V to the relay Coil + (12V) and - (Gnd)

Connect RF sources to the relay

Connect USB cable to the computer. It should find the driver. If you are using virtual com ports, you

will need to assign this one to a high COM number to not interfere.

Here is everything connected together

Fire up the Arduino IDE and load the code listed below into the Nano.

Fire up a terminal program. You can use the serial monitor in the Arduino IDE or any program that can talk to a serial port. I use 115200 Baud.

You can then command the relay. Send an “A” or “a” to select channel A. Send a “B” or a “b” to select channel B. On startup the Nano will select A, wait a second, select B and then say it is ready for commands. When you send a command it will echo back the switch position.

Notes:

This can be expanded to use more TTL outputs to control more or different relays. Some relays have indicator outputs and you can read those back with the Nano.

This is not galvanically isolated. If you need that, you can get USB isolators.

You may need to add ferrite beads depending on power levels.

Arduino Sketch

int inByte=0;

void setup() {

// initialize serial:

Serial.begin(115200);

pinMode(13, OUTPUT);

pinMode(2, OUTPUT);

pinMode(3, OUTPUT);

Serial.print("Serial Init\n");

digitalWrite(13, HIGH); // turn the LED on (HIGH is the voltage level)

digitalWrite(2, HIGH);

digitalWrite(3, LOW);

Serial.print("CH A ON\n");

delay(1000); // wait for a second

digitalWrite(13, LOW); // turn the LED off by making the voltage LOW

digitalWrite(2, LOW);

digitalWrite(3, HIGH);

Serial.print("CH B ON\n");

Serial.print("Ready for Commands\n");

}

void loop() {

if (Serial.available() > 0) {

// get incoming byte:

inByte = Serial.read();

if ((inByte == 0x41)||(inByte == 0x61)) { // "A" or "a"

digitalWrite(13, HIGH);

digitalWrite(2, HIGH);

digitalWrite(3, LOW);

Serial.print("Ch A ON\n");

}

if ((inByte == 0x42)||(inByte == 0x62)) { // "B" or "b"a

digitalWrite(13, LOW);

digitalWrite(2, LOW);

digitalWrite(3, HIGH);

Serial.print("Ch B ON\n");

}

}

}

Copyright Note:

All content Copyright (C) 2017 by Mark Goldberg.

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Last Edited 4 December 2017