Why is IR Transceiver transmitting/receiving rubbish

infraredmicrocontrollerwireless

I am trying to interface two microcontrollers wirelessly using IR transceivers. The microcontroller I'm using is ATMega164PA running on a 3.3V supply at 8MHz and the transceiver is TFDU4101-TR3. I am using serial communication for both. When I try to send a character 10 times from one transceiver to another, I get a range of numbers between 255 and 193. Is there something that I'm doing wrong? Even if I send any other character I get the same rubbish.

Also, can I write my own protocol to establish communication between the two devices?

A schematic of my setup is shown below:

enter image description here

Best Answer

Sounds like either a baud rate mismatch or a start bit detection problem. Characters between 255 and 193 mean bits 7 and 6 are always set (0b11000000==192), as well as some lower bit (which are earlier in the serial sequence). Remarkably the receiver idles with RXD high while the transmitter should be inactive with TXD low; this combination could cause unexpected behaviour of the start bit, as the AVR transmitter will idle high. Not being familiar with the IrDA signaling standards, I would probably take an oscilloscope to the signal to examine if RXD is simply inverted from TXD.

If we do have inverted polarity behaviour, we expect a transmission like ...1111110dddddddd111111... to turn into ...111111xx0DDDDD00...0001111..., with the first 0 lost as no transmission, the 0 detected as start bit matching the least significant 1 of the transmitted byte, but the stop bit 1 would be inverted marking the framing error. At a later point, the 0 would be detected as a start bit, and eventually the transmitter times out, causing the appearance of a byte with a pattern 11...00 which does not have the frame error detected. All the data bits that are received are inverted and in the wrong position. The xes represent transmitted 0s which go undetected as the transmitter switches from not sending due to too long pulse to not sending because the value is 0. If this is the behaviour, a logic inverter on TXD should solve it.

Atmel's application note AVR1303, Use and configuration of IR communication module, covers a peripheral meant to talk to this type of transceiver. It should show what sort of signaling is normally used. By the looks of it, the format used is one pulse per 0 bit only, so direct connection to the USART is not the way to go.

Related Solutions

Electronic – MRF49XA Microchip Transceiver

The demo code is for a PIC18F87J11 and the C18 compiler, whereas you are using a PIC16F886 and some other, probably incompatible, compiler.

You will probably have more success if you use a PIC18 instead of the PIC16F886, with the C18 compiler. I downloaded the code, and apart from having to fix the include file location, the application built without any problems. You are also more likely to get assistance if you use the correct chip and compiler, either from people here, or on the Microchip forum.

How to get data from one micro controller to another using UART

I dont understand your confusion. You want to communicate between the two controllers with UART, then ofcourse both of them need UART capabilities and code for this. Your computer has drivers and software for dealing with this, so your microcontroller also needs a driver for it.

Your ATmega32 need UART TX functionality, while AT90USB1287 need UART RX functionality. Having already written both TX and RX for your ATmega32, writing the UART RX routine for AT90 should be a breese. You could add a bitvalue of some kind, identifying that the UART RX on AT90 is coming from your ATmega32, and directly pass it through to USB.

EDIT: Code from AVRFreaks that is written for at90usb1287

#include <avr/io.h> 
#include <util/delay.h> 

#define RXC      (RXC1) 
#define TXC      (RXC1) 
#define UCSRC    (UCSR1C) 
#define UCSRB    (UCSR1B) 
#define UCSRA    (UCSR1A) 
#define UDR      (UDR1) 
#define UBRRL    (UBRR1L) 
#define UBRRH    (UBRR1H) 
#define UBRR     (UBRR1) 
#define UDRE     (UDRE1) 
#define RXCIE    (RXCIE1) 
#define TXEN     (TXEN1) 
#define RXEN     (RXEN1) 
#define UCSZ0    (UCSZ10) 
#define UCSZ1    (UCSZ11) 
#define UMSEL0   (UMSEL10) 
#define UMSEL1   (UMSEL11) 

#define FRAMING_ERROR (1<<FE1) 
#define PARITY_ERROR (1<<UPE1) 
#define DATA_OVERRUN (1<<DOR1) 
#define DATA_REGISTER_EMPTY (1<<UDRE1) 
#define RX_COMPLETE (1<<RXC1) 

#define FOSC 16000000 

typedef unsigned char       Uchar; 
typedef unsigned long int   Uint32; 

#define Wait_USART_Ready() while (!(UCSR1A & (1<<UDRE1))) 

#define lowByte(w) ((uint8_t) ((w) & 0xff)) 
#define highByte(w) ((uint8_t) ((w) >> 8)) 

int main(void) 
{ 
/* Disable clock division */ 
clock_prescale_set(clock_div_1); 
   UBRRH = (Uchar)((((Uint32)FOSC)/((Uint32)USART_BAUDRATE*16)-1)>>8); 
   UBRRL = (Uchar)(((Uint32)FOSC)/((Uint32)USART_BAUDRATE*16)-1) & 0x0ff; 

   UCSRB |= (1 << RXEN) | (1 << TXEN); 
   UCSRC |= (1 << UCSZ1) | (1 << UCSZ0); 

   char ReceivedByte; 
   for (;;) // Loop forever 
   { 
      while ((UCSRA & (1 << RXC)) == 0) {}; // Do nothing until data have been received and is ready to be read from UDR 
      ReceivedByte = UDR; // Fetch the received byte value into the variable "ByteReceived" 

      while ((UCSRA & (1 << UDRE)) == 0) {}; // Do nothing until UDR is ready for more data to be written to it 
      UDR = ReceivedByte; // Echo back the received byte back to the computer 
   } 
}

Best Answer

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Electronic – MRF49XA Microchip Transceiver

How to get data from one micro controller to another using UART

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