AVR Freaks

Implementing of pulses is pretty easy with ATtiny202. I don't need to use micros() but I will use TCB in Periodic or Single Shot mode (e.g. 80µs for Triac control).

I have decided to start from scratch with ATtiny202 and follow the Manchester Encoder Using USART and CCL on ATtiny817. It is running well on standard ATtiny202 frequency 20 MHz / 6 = 3.333 MHz and 9600 bits/s.

ATtiny202 same result as in the AN2371 example above:

Although I found the OregonScientific-RF-Protocols (need version 2.1) I do not fully understand how to generate the "sauce" around Manchester encoded temperature data.

Finally I succeeded. I can now transmit temperature data from the ATtiny202 through 433 MHz transmitter to the Oregon Scientifics base station.
 

I am going to make a final version of the program with sleep mode to transmit data each 30 seconds. The ATtiny202 clock 20 MHz is devided by 24 to 833333 Hz to save the power consumption and to get the 1 024 Hz bit rate. I am using synchronous USART and  Configurable Custom Logic (CCL) to generate Manchester code.
 

The program uses 103 out of 128 bytes of RAM and 932 out of 2 048 bytes of Program Flash.

Attached you can find my MPLAB X IDE working test project which sends temperature 12.3°C each 30 seconds to the Oregon Scientific base station 259981. The ATtiny202 is simulating the Oregon Scientific THN132N Wireless Temperature Sensor.

The THN132N is using Oregon Scientific protocol 2.1 and 1024 Hz bit rate. 1024 BAUD doesn't work but 1028 BAUD Yes.

The ATtiny202 clock 20 MHz is divided by 24 which is 833333 Hz. Synchronous IRQ USART routines generated at start.atmel.com

ATtiny202 pins PA3 (SOIC 7) CLK, PA1 (SOIC 4) TX and PA6 (SOIC 2) is the Manchester code output to 433 MHz transmitter.

Message structure (send twice with pause 6.42 ms between these two messages and then long pause 30 seconds):

After test while (USART_0_tx_elements != 0) there ares s till two USART registers shifting data out (USART buffer ~ 19.64 ms)   

So you need actually set delay to 29 ms to get 6.42 ms pause (29 -  19.64 = 9.36 ms)

_delay_ms(29); // ~6.42 ms; USART buffer ~ 19.64 ms

Preamble 16 pulses (i.e. send 4x 0xAA)
Sync, send 1x 0x99 which is in Manchester 0xA

Actual Data Test Data

Nibble:

  0  0xE  Sensor Id: 0xEC40 (THN132N)

  1  0xC

  2  0x4

  3  0x0

  4  0x4  Channel No. = 3  (1<<(ch-1))

  5  0x6  Rolling Code, Value changes randomly every time the sensor is reset (it's up to you)

  6  0x8 

  7  0x0  Battery voltage 0 = OK (Bit value 0x4 is the battery low flag)

  8  0x3  Temperature, tenth of a degree (BCD temperature in degrees Centigrade i.e 12.3°C)

  9  0x2  Temperature, units of degrees

10  0x1  Temperature, tens of degrees

11  0x0  Temperature sign, 0 = positive temperature (Non-zero for negative values)

12  0x6  Checksum (of nibbles 0 to 11) i.e. 0x36

13  0x3

14  0xD  CRC* nibbles 0 to 11 excluding Rolling Code (Nibbles 5 and 6), start CRC value = 0x43, polynomial = 0x07

15  0x7

CRC calculation is not part of the test program yet. I calculated it in Visual Studio C++:
 

#include <stdio.h>
#include <stdlib.h>

#define CRC8INIT  0x43
#define CRC8POLY  0x07

char msglen = 5;
unsigned char msg[] = { 0xEC, 0x40, 0x40, 0x32, 0x10 };	// CRC 0x7D, for my test program

unsigned char crc8(unsigned char* data_in, char number_of_bytes_to_read) {

	unsigned char  crc, loop_count, bit_counter;

	crc = CRC8INIT;

	for (loop_count = 0; loop_count != number_of_bytes_to_read; loop_count++)
	{
		crc = crc ^ data_in[loop_count];

		bit_counter = 8;
		do {
			if ((crc & 0x80) != 0) {
				crc <<= 1;
				crc = crc ^ CRC8POLY;
			}
			else crc <<= 1;
			bit_counter--;

		} while (bit_counter > 0);
	}

	return crc;
}

int main()
{
	unsigned char crc;
	crc = crc8(msg, msglen);
	printf("\r\n crc %2x", crc);
	return (0);
}

Just to let make the PCB. U1 is the Microchip MCP16251 (high-efficiency, fixed frequency, synchronous step-up DC-DC converter 1.5 to 3.3V), U2 ATtiny202 and U3 is the 433 MHz transmitter.
 

What's wrong ?

I can't do much more because of the constraints (AA battery next to "+" sign, two holes) of the PCB layout to fit into the Oregon temperature sensor casing. I can only move R2 & C2 closer to the U1 voltage converter chip. Tracks are 0.3 mm (11.811 mils).
 

See the design of the Microchip Evaluation Board: