Never did get a picture of this project running

The idea is that an SMS phone can be used to receive SMS messages that can then be displayed on a large format message board.

Hardware Description
Atmel AVR Microcontroller Development System
This kit was kindly provided to me by the friendly people over at
8×24 LCD Display
Details of how to wire up a 8×24 display to the development board can be found at (see the 8×24 LCD Project). If you use a smaller display then you will have to modifying the code to suit.
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
  • As the ATMEL AT90S2313 only has 2k of code space the demo version of BASCOM can be used without hitting any of its restrictions.
  • Hyperterminal or any suitable terminal emulation package. Useful for making sure that your GPS unit is tranmitting data.

A great site for the wiring of all things RS232 can found at

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

Pin Signal Specs
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
6 MBus 9600bps
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
9 LGnd

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.

AVR RS232 DB9 wiring The DLR-3 cable expects partial handshaking from a DCE. The problem is the AVR board does not implement any hardware handshaking and is wired as a DTE.

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
1 5 Signal ground
2 3 Tx → Rx
3 2 Rx → Tx
4 4 Vcc → DTR

[#Beginning of Shooting Data Section]
Nikon COOLPIX3100
Focal Length: 10.2mm
White Balance: Auto
Digital Zoom Ratio: 1.00
2005/02/19 14:02:22
Exposure Mode: Programmed Auto
AF Mode: AF-C
Saturation comp: 0
JPEG (8-bit) Normal
Metering Mode: Multi-Pattern
Tone Comp: Auto
Sharpening: Auto
Image Size:  640 x 480
1/89.9 sec - F/3.6
Flash Sync Mode: Red Eye Reduction
Noise Reduction: OFF
Exposure Comp.: 0 EV
ConverterLens: None
Sensitivity: Auto

The purpose of this null modem cable is to make the phone think there is a DCE device listening

  • atmel/smsrx.txt
  • Last modified: 2012/07/09 11:43
  • by minerva9