Published March 17, 2019 © GPL3+

12-Channel USB-Powered Relay Board

A very simple USB board that allows you to control 12 relays for lighting, open electric gates, etc.

BeginnerFull instructions provided2 hours2,125

Things used in this project

Hardware components

ITACA Innovation uChip

Available on https://shop.itaca-innovation.com

onsemi BC337-40

3.3 kOhm, 1/4W, 5% resistor (TH)

This resistor value isn't critical. Can be lowered or increased (up to 15k is fine).

1.5 kOhm, 1/4W, 5% resistor (TH)

Adjust it to achieve your desired luminosity. Our LEDs were very bright. Much smaller value (e.g. 330 Ohm) might be required for other kinds of LED. We used precision resistors just because we had a reel of them (and no 1.5 kOhm 5%!).

100 uF Capacitor, WV >= 6.3V

270 Ohm, 1/4W, 5% resistor (TH)

2-poles screw terminal, 5.08 mm spacing

The 13th is required only if you want to externally provide 5V

10x16 cm perfboard

You just need 6.35x16 cm, but that's not a standard board! You can also use a PCB.

5 mm LED: Red

Any LED.

3 mm LED: Red

In our project we used a .1.8 mm LED.

1N4148 – General Purpose Fast Switching

TE Connectivity PCN-105D3MHZ relay

KS-01Q-01 pushbutton

Optional user buttons. You can modify the sketch to have them do something!

HEX STANDOFF M3 NYLON 6MM (e.g. CBMFTS210A)

Micro-USB to USB Cable (Generic)

16-PIN DIP IC SOCKET

HEX nylon NUT

Software apps and online services

Arduino IDE

Hand tools and fabrication machines

Soldering iron (generic)

Story

note! This project is kept up to date on next-hack.com!

Introduction

Sometimes controlling various kind of loads using a PC/Mac is desirable: one can choose his/her preferred high level language, programming environment. Loads can be easily and inexpensively switched using relays.

However, one must put some kind of interface between relays and the PC.

An USB-controlled board is a very advantageous solution: you can hook it up to any PC/Mac with an USB port and it also can draw directly the required power from it.

This very simple project allows you to control up to 12 relays. The chosen relays allow to switch (resistive) loads up to 3A. If heavier loads must be switched, then one can either put a more rugged relay, or can use these relays as a switch, to control bigger relays close to the loads.

The current consumption with all the relays in ON state is less than 350 mA, so any standard 500-mA USB compliant port should be adquate.

We used uChip, which is an Arduino Zero compatible board shrunk to a 16 DIP package. This allows us to make a compact design.

Two pushbuttons are added to extend the functionality of the board (e.g. emergency shutdown, sequence ecc...) These functionalities are left open to your immagination!

Theory of operation

The device waits for a serial connection on the USB port (CDC). Once a connection has been established, it periodically listens for commands.

The commands are as follows:

Capital letters A to L select the relay(s) you want to turn on or off. For instance ACF will select the first, the third, and the sixth relays. A subsequent 0, will turn off all the selected relays. A subsequent 1 will turn the selected relays on. Any other characters (including lower case a-l and 2 etc.) will abort the command.

For instance "ACF1" will turn on relays A, C and F.

If we write "CF0", the relays C and F will be turned off.

Any combination of relays can be turned on/off simultaneously.

Each relay is connected to uChip using a BJT. The LEDs show the state of the channels.

Preparation

In these steps we use a 10x16 cm perfboard. Of course, you can also manufacture the PCB following the layout.

1) Measure 6.35 cm on the perfboard.

2) Cut the perfboard along the line.

3) Use a file to smooth the edges.

4) Mark the position for the holes.

SAFETY WARNING! If using 110-240 V loads, then place the holes a bit farther than what's shown here, especially near the screw terminal blocks. Alternatively do not use metal stand-off, but plastic ones as suggested in the component list.

5) Drill the holes.

6) Solder all the components, in order of height. Resistors, IC socket, BJTs, diodes, 5-mm LED, screw terminal blocks, capacitor, the other LEDs, relays, pushbuttons.

Keep the component leads. These will be useful later for the connections!

7) After soldering the components, remove the extra pads around the relays and screw terminal blocks, ti improve insulation. This can be done using the soldering iron. Be sure to use a sacrificial tip and not your good one!

8) Make the connections using the wires you cut from the components. Use additional wire when no space is left. :-)

9) Insert uChip, connect the board with a microUSB cable and program uChip using the sketch provided and Arduino IDE.

10) Use your favourite terminal program (serial monitor, termite, etc.) and write a test string to see if it works. For instance, entering ABCDEFGHIJK1 will cause all LEDs will turn on.

11) Enjoy!

Code

Sketch for the relay board

/* Simple USB relay controller for uChip. Copyright 2019 Nicola Wrachien www.next-hack.com 
 * 
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *  
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.   
 * 
 ****************************************************************************************
 * USAGE:
 * Open a serial connection, and first write the relays you want to operate (A = relay 0, 
 * B= relay 1, and so on), and then write 1 to switch them on, or 0 to switch them off.
 * Any other character will abort the command.
 * 
 * Examples (remove quotes "):
 * "ABC1"     // turns on relays 0 (A), 1 (B), 2 (C) 
 * "BD0"      // turns off relays 1 (B) and 3 (D). 
 * (assuming you have 12 relays):  "AQ1"    (aborts the command once Q has been received. 
 *                                1 does nothing, because no relay was selected after Q)
 * "ABC2": aborts the command, as 2 is not a valid character.
 */
uint32_t time;
uint32_t relays = 0;
//const uint8_t pins[] = {1, 2, 3, 4, 5, 6, 10, 9, 7, 15, 12 , 11};
const uint8_t pins[] = {1, 2, 3, 4, 5, 6, 7, 15, 12,  11, 10 , 9};

void setup() 
{
  // set all outputs default low.
  for (int i = 0; i < sizeof(pins); i++)
  {
    pinMode(pins[i], OUTPUT);  
    digitalWrite(pins[i], 0);
  }
  // set output to 5V
  REG_PORT_DIRSET0 = PORT_PA15;
  REG_PORT_OUTSET0 = PORT_PA15;  // Quickly enable 5V buck regulation!
  // open serial and wait till it's ready!
  SerialUSB.begin(9600);
  while (!SerialUSB);
  pinMode(LED_BUILTIN, OUTPUT);
}
void loop() 
{
  if (millis() - time > 1000)
  {
    time = millis();
    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
  }
  // now get some data and process it
  if (SerialUSB.available() > 0)
  {
    char c =SerialUSB.read();
    if (c >= 'A' && c < 'A' + sizeof(pins))       
    {
      relays |= 1 << (c - 'A');   // set to one the bit corresponding to the relay we want to turn off/on
    }
    else if (c == '0')
    { // we want to turn off all the previously selected relays.
      for (int i = 0; i < sizeof(pins); i++)
      {
        if (relays & (1 << i))
          digitalWrite(pins[i], 0);
      }
      relays = 0; // deselect relays
    }
    else if (c == '1')
    {
      for (int i = 0; i < sizeof(pins); i++)
      {
        if (relays & (1 << i))
          digitalWrite(pins[i], 1);
      }      
      relays = 0; // deselect relays
    }
    else // any other chars... cancel the command
      relays = 0;    
  }
}

Credits

Nicola Wrachien

3 projects • 2 followers

I was born, then I got my master, a PhD. I forgot about all what's in between.

12-Channel USB-Powered Relay Board

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Introduction

Theory of operation

Preparation

Schematics

Schematics

Example of LLayout

Complete KiCAD project

Code

Sketch for the relay board

Credits

Nicola Wrachien

Comments

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12-Channel USB-Powered Relay Board

12-Channel USB-Powered Relay Board

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Introduction

Theory of operation

Preparation

Schematics

Schematics

Example of LLayout

Complete KiCAD project

Code

Sketch for the relay board

Credits

Nicola Wrachien

Comments

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