{"id":263,"date":"2010-11-14T02:20:37","date_gmt":"2010-11-14T02:20:37","guid":{"rendered":"http:\/\/louisc.co.uk\/FYP\/?p=263"},"modified":"2016-11-05T11:17:47","modified_gmt":"2016-11-05T11:17:47","slug":"experiment-connecting-up-and-testing-the-rf12-trx433s-modules","status":"publish","type":"post","link":"https:\/\/louisc.co.uk\/?p=263","title":{"rendered":"Experiment – Connecting up and testing the RF12 \/ TRX433S modules"},"content":{"rendered":"

Experiment Aim<\/span><\/h1>\n

The aim here is to Setup two wireless modules and use the RF12_Demo application provided with the JeeLabs <\/a>library to drive the modules.\u00a0Special attention will be paid to the robustness of the signal at range.<\/p>\n

A secondary aim is to gain an understanding into how the library is driving the modules and begin to think about how I will implement them.<\/p>\n

Predicted Outcome<\/h2>\n

The specifications on the module say that they can reach a maximum distance of 300m. It must be assumed this will be in ideal conditions with no obstacles or\u00a0interference\u00a0 and hence direct line of sight. This will also assume correct antenna use. A prediction of around 20-30m would be impressive considering testing is being carried out in the Undergraduate Engineering labs which are densely filled with electronic equipment.<\/p>\n

Setup<\/span><\/h1>\n

After reading through the documentation provided with the library the following setup was chosen:<\/p>\n

Circuit<\/h2>\n

The following diagram illustrates the circuit to be used and how it will be connected on the breadboard:<\/p>\n\n\n\n\n
\"\"<\/a><\/td>\n<\/tr>\n
Test circuit Setup for the Alpha transceiver module. (RF12)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

This was worked out by looking at the header files of the library:<\/p>\n

\/\/ ATmega328, etc.\r\n#define RFM_IRQ     2\r\n#define SS_PORT     PORTB\r\n#define SPI_SS      5\r\n#define SPI_MOSI    11\r\n#define SPI_MISO    12\r\n#define SPI_SCK     13<\/pre>\n
These were referenced with the\u00a0pin out\u00a0diagram of the transceiver module:<\/p>\n
\n\t\t\t\t\t
\n\t\t\t\t\t\t
\"Pin-out<\/a>
Pin-out for ALPHA RF module (From Data Sheet)<\/p><\/div>\n
Code – “RF12demo” (Relevant excerpts<\/em>)<\/h2>\n
A look into what the demo code is doing to better understand what is going on. The microcontroller (MCU) was flashed with the demo program. A serial console was then opened on the computer it was connected to and a serial connection established.<\/p>\n
Setup code:<\/h3>\n
This is the code which will be run before entering the main loop. I have used comments to better explain what it does.<\/p>\n
void setup() {\r\n      \/\/Initialize a serial connection with the\r\n      \/\/computer at 27600 baud\r\n      Serial.begin(57600);\r\n      \/\/A simple print via serial connection\r\n      Serial.print(\"\\n
<\/div>\n\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>
\n\t\t\t\t\t
\n\t\t\t\t\t\t[RF12demo.6]\");\r\n      \/\/First check EEPROM memory for stored configuration,\r\n      \/\/if nothing is found it will default to the else statement\r\n      if (rf12_config()) {\r\n         config.nodeId = eeprom_read_byte(RF12_EEPROM_ADDR);\r\n         config.group = eeprom_read_byte(RF12_EEPROM_ADDR + 1);\r\n     }\r\n     \/\/ The default settings if no previously stored\r\n     \/\/configuration is found in EEPROM\r\n     else {\r\n         config.nodeId = 0x41; \/\/ node A1 @ 433 MHz\r\n         config.group = 0xD4;\r\n         saveConfig();\r\n     }\r\n\r\n      \/\/This will run the show help function which\r\n      \/\/prints text containing commands to the screen\r\n      showHelp();\r\n }<\/pre>\n
Before continuing a look at the commands this demo program allows. This is the code that the “showHelp” function prints to the serial connection,\u00a0useful\u00a0commands have been commented:<\/p>\n
char helpText1[] PROGMEM =\r\n    \"\\n\"\r\n    \"Available commands:\" \"\\n\"\r\n    \/\/ This will allow setting of ID in EEPROM -----------------\r\n    \"   i     - set node ID (standard node ids are 1..26)\"\r\n    \"           (or enter an uppercase 'A'..'Z' to set id)\"\r\n    \/\/ ------------------------------------------------------\r\n    \"   b     - set MHz band (4 = 433, 8 = 868, 9 = 915)\"\r\n    \"   g     - set network group (RFM12 only allows 212, 0 = any)\"\r\n    \"   c     - set collect mode (advanced, normally 0)\"\r\n    \/\/ ------Our main method of testing will be using this-----\r\n    \"   t     - broadcast max-size test packet, with ack\"\r\n    \"  ..., a - send data packet to node , with ack\"\r\n    \/\/ ------------------------------------------------------\r\n    \"  ..., s - send data packet to node , no ack\"\r\n    \"   l     - turn activity LED on PB1 on or off\"\r\n    \"   q     - set quiet mode (1 = don't report bad packets)\"\r\n;<\/pre>\n
Main Loop<\/h3>\n
Now the initialization of the device is complete it will fall into its main loop where it will wait for instructions via serial or received packets via the wireless module. Some relevant code excerpts have been explained below: The first condition we have will check whether there is any information on the serial buffer. If there is it will read the data into the function handleInput().<\/p>\n
    if (Serial.available())\r\n        handleInput(Serial.read());<\/pre>\n
Inside “handleInput” is a simple set of switch case statements. I have included below the switch case statements for the highlighted commands above:<\/p>\n
If ‘i’ is send to the board via serial the following code is executed:<\/p>\n
case 'i': \/\/ set node id\r\n        config.nodeId = (config.nodeId & 0xE0) + (value & 0x1F);\r\n        saveConfig();\r\n        break;<\/pre>\n
So simply put when ‘i’ is selected the variable “nodeId” in class config is filled. The config is then saved. If ‘t’ is selected the following is run:<\/p>\n
case 't': \/\/ broadcast a maximum size test packet, request an ack\r\n        cmd = 'a';\r\n        sendLen = RF12_MAXDATA;\r\n        dest = 0;\r\n        for (byte i = 0; i < RF12_MAXDATA; ++i)\r\n             testbuf[i] = i;\r\n        break;<\/pre>\n
The task here is to broadcast a test packet of the maximum size available and request an acknowledgement. If this is broken down:<\/p>\n