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!