{"id":491,"date":"2019-03-30T11:14:55","date_gmt":"2019-03-30T10:14:55","guid":{"rendered":"https:\/\/next-hack.com\/?p=491"},"modified":"2020-06-05T21:18:00","modified_gmt":"2020-06-05T19:18:00","slug":"a-simple-12-channel-usb-controlled-relay-board-part-1","status":"publish","type":"post","link":"https:\/\/next-hack.com\/index.php\/2019\/03\/30\/a-simple-12-channel-usb-controlled-relay-board-part-1\/","title":{"rendered":"A simple 12-channel USB controlled relay board (part 1)"},"content":{"rendered":"\n

Introduction<\/h3>\n\n\n\n

In the Internet of Things (IoT) era, being able of controlling everything is becoming more and more requested. The most common example is the home automation: one would like to control for instance lights, the gates, and even appliances. One could use advanced wireless and custom solutions, but this adds difficulty to the task, and discourages many people. A much simpler way is to connect directly a relay board to a PC\/Mac: one can choose his\/her preferred high level language programming environment. Relays allow easy and inexpensive control of loads.<\/p>\n\n\n\n

How to connect relays to a PC? Of course via USB! 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.<\/p>\n\n\n\n

Despite its simplicity, this project will allow 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.<\/p>\n\n\n\n

The board is USB compliant, as the current consumption with all the relays in the ON state is less than 350 mA.<\/p>\n\n\n\n

We used\u00a0uChip<\/a>, which is an Arduino Zero compatible board shrunk to a 16 DIP package. This allows us to make a compact design. Actually you might use anything you want that has an USB connection and enough I\/O pins.<\/p>\n\n\n\n

In this project we also put two pushbuttons which might be used for testing purposes, or emergency buttons, or other things. These functionalities are left open to your immagination!<\/p>\n\n\n\n

Part 1 will cover the full project, which allows to control the board using a PC\/MAC or even a Raspberry.
Part 2 will cover the USB Host implementation, that allows to connect a 3G dongle, and to allow to control the relays using SMS.<\/p>\n\n\n\n

Theory of operation<\/h3>\n\n\n\n

The device waits for a serial connection on the USB port (CDC). Once a connection has been established, it periodically listens for commands. You might use any baud rate, as the USB device implements a virtual COM port.<\/p>\n\n\n\n

The commands are as follows:<\/p>\n\n\n\n

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 2-9 etc.) will abort the command.<\/p>\n\n\n\n

For instance “ACF1” will turn on relays A, C and F.<\/p>\n\n\n\n

If we write “CF0”, the relays C and F will be turned off.<\/p>\n\n\n\n

Any combination of relays can be turned on\/off simultaneously.<\/p>\n\n\n\n

Each relay is connected to uChip using a BJT. The LEDs show the state of the channels.<\/p>\n\n\n\n

Here is the schematics PNG and here the KiCAD project!<\/a><\/p>\n\n\n\n

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Downloads<\/h2>\n\n\n\n

Click here for the full KiCAD project.<\/a><\/p>\n\n\n\n

Click here for the Arduino sketch!<\/a><\/p>\n\n\n\n

Hardware requirements<\/h3>\n\n\n\n