This project details how to connect Opto-Isolated Relay Board to an AVR development board and control it via Text message (SMS)
BASCOM Source Code
What is needed
| Atmel AVR Microcontroller Development System
This kit was kindly provided to me by the friendly people over at http://www.btinternet.com/~e2one/avrbrd/
| 8×24 LCD Display
Details of how to wire up a 8×24 display to the development board can be found at http://www.btinternet.com/~e2one/avrbrd/ (see the 8×24 LCD Project). If you use a smaller display then you will have to modifying the code to suit.
| Relay board
Opto-Isolated Relay Board, includes 4 channels for remote control of Mains appliances and circuits. Ideal for home control and industrial applications. Each channel is controlled by a TTL input and can easily be controlled by a microcontroller or control system.
| Relay cable
Cable to wire the AVR board to the relay board
| A mobile phone
I used a NOKIA 7110 but any phone that has a built in modem should be ok.
| A DLR-3 cable
A phone connector wired to a DB9-F
If you don't have one or you can't afford to buy it then there are some good solutions for making your own.
A great site for the wiring of all things RS232 can found at http://www.lammertbies.nl/comm/cable/RS-232.html
9 Pin Connector on a DTE device (Phone connection)
|Pin Number||Direction of signal:|
|1||Carrier Detect (CD) (from DCE) Incoming signal from a modem|
|2||Received Data (RD) Incoming Data from a DCE|
|3||Transmitted Data (TD) Outgoing Data to a DCE|
|4||Data Terminal Ready (DTR) Outgoing handshaking signal|
|5||Signal Ground Common reference voltage|
|6||Data Set Ready (DSR) Incoming handshaking signal|
|7||Request To Send (RTS) Outgoing flow control signal|
|8||Clear To Send (CTS) Incoming flow control signal|
|9||Ring Indicator (RI) (from DCE) Incoming signal from a modem|
Nokia 7110 DLR-3
|1||V In||0..8.5V, 0..850mA|
|2||Chrg Control||PWM, 32..37 Hz, 1..99%|
|3||XMic / Device Selector|
|4||SGnd / DLR-3 VCC||3.3 V|
|5||XEar / DLR-3 RTS|
|7||FBus Rx / Modem|| 9600 - 230.400 bps
< 0.8V : '0'
> 2.0V : '1'
|8||FBus Tx / Modem|| 9600 - 230.400 bps
< 0.8V : '0' @ max. 4mA > 1.7V : '1' @ max. 4mA
Inside the AVR cable
The standard cable that is supplied with the AVR development kit uses a 3 pin configuration for RS232 data. It is wired as a DTE with built in loop back handshaking.
To overcome this problem we will build a new cable. This will be wired so that the AVR board is seen as DCE, additionally it will also have a hardwired active DTR signal.
|AVR board IDC||Connector||Function|
|2||3||Tx → Rx|
|3||2||Rx → Tx|
|4||4||Vcc → DTR|
The purpose of this null modem cable is to make the phone think there is a DCE device listening
So to wire a suitable cable the following mapping can be used
|LCD Board||6 Pin IDC|
|3||Out0 - PB2|
|5||Out1 - PB3|
|12||Out2 - PB4|
|13||Out3 - PB7|