Products > Test Equipment
Brymen IR connection protocol - Anyone sniffed it yet?
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jadew:
Alright, I just gave it a try, I sent the 10ms pulse, but to no avail.

Are you sure there's no other data sent from the device to the meter when communication starts? Like... when you start the software that controls it?

Edit:
I guess a good test would be to leave the device disconnected from the meter and see what happens, it should try to sync with the meter.
Simon Loell:
I will try to measure the TX line without the multimeter connected tonight. (In 10 hours from now).

Did you send the 10ms pulse wait for about 120ms, and then start sending 160 clock cycles?

I would imagine the communication is like SPI, but without MOSI (Master Out Slave In) and CS (Chip Select). Where the PC is the master giving the CLK (syncronous Clock) and the multimeter sending data in sync on MISO (Master In Slave Out).

What platform are you testing via?

I could hook up an AVR on both a STK600 board or just use a simple Arduino Uno to generate the clock cycles, read back from multimeter, pack the 160 bits into 20 bytes and send to a PC over the UART.
jadew:
Hey, I did not send the clock, because from the last screenshots, it looks like the meter does something first and only then the clock starts rolling.

I think that after the meter is initialized, things happen like this:
Tx: 10 ms pulse
Rx: goes high
Tx: starts rolling the clock

This is visible in the picture called "BM869 link startup close-up on beginnning on first data packet".

From that picture we can also conclude that the falling edge of the clock is the setup edge and the rising one the sample edge. You can pretty much tell why communication happens at this speed based on the response of the meter to the falling edge (it's way off).

I'm testing it with an AVR and a temporary "adapter" I made from cardboard. The receiver diode is connected in series with a resistor, between vcc and gnd and I'm probing between the resistor and the diode with the scope. Once the diode starts conducting, the line will get high (tested it, the receiver works).

Edit: It would be useful if you could tell me which one is the RX and which one is the TX diode on the meter, because they're the same color and I have to reverse the "adapter" for each test I'm making :)
Simon Loell:
Which AVR are you using?
What compiler?
What clock rate etc.

If you give me the details, I will try to mock up a setup exactly identical. In that way we can exchange our code.

Regarding the IR diode and phototransistor, can you make a schematic - just a handwritten, so no misunderstandings will occour.
jadew:
I'm using an attiny2313.

Compiler: avr-gcc, altho the code at this point is just a pulse generating thingie, so nothing special there.

Using the internal 8Mhz clock, however, the timing for this protocol should be easily met with pretty much any clock speed.

As you can see from the code, there's not much to it at this point. Also, if you're going to use that makefile, make sure you're changing the fuse settings to match the chip you're testing on, otherwise you might brick it.
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