Digispark Controls Relay Via GSM

This instructable uses a Digispark board, together with a relay and GSM module to turn on or off and appliance, while texting the current state to a predefined phone number(s).

The code is very crude, responsive to any communication from the module to the Digispark (includes a phone call, text message, anything that triggers a communication).

It automatically hangs up roughly after 4 dialing tones, in case of a phone call.

Step 1: Setting Up

This project involves the following:

- 1 Digispark module using an ATtiny85 AVR MCU;

- 1 A6 GSM module with valid SIM card;

- 1 5V relay module

- Some wires;

- A box to put this in to (I'm still missing this);

- Something to turn on or off!

Step 2: Connections and Programming

The software I wrote uses pin 0 for actuating the relay, pin 2 as serial receive and pin 3 as serial transmit.

As the Digispark has no UART, we are using SoftwareSerial library.

Pin 0 is connected to the relay board's input (I mounted my Digispark via headers to the relay board), Pin 2 connects to the GSM module's Tx pin and Pin 3 connects to the GSM module's Rx pin.

I chose pin 3 as Tx as it already has a 3.4V zener clamping diode for USB communication/programming, while the GSM module uses 2.8V logic, according to the datasheet. I haven't had any issues until now, since communication is set to a minimum.

5V and ground are taken from the GSM board.

Step 3: Ready to Use!

Program the Digispark with the included code, not forgetting to replace "xxxxxx" and "yyyyyy" with you recipient's phone number.

Connect a lamp or other load under 10A to the relay, dial the GSM module phone number and you'll be presented with a clicking sound and an SMS indicating if the relay is On or Off!