Reading Wireless Air Transmitter using Arduino

[TheScubaPanda]

How hard would it be to make a stand alone p02 meter wirelessly... I can make a wired one no problem.... but wireless is a bit beyond me....

Technically very easy with an arduino. Now, making that waterproof with reliable enough hardware ...

 

[TheScubaPanda]

1. Presumably no, the swift just checks to see that the channel is clear. Since it is backwards compatible.
2. No, just good, low, or critical
3. As far as I can tell yes. Pelagic Pressure Systems designed the protocol and original transmitters, they're based in San Francisco, California.

We can wirelessly transmit nearly any info from back mounted hardware to a watch/ computer, the hard parts is hardware/software integration. These transmitters work great for pressure but only pressure. It would be possible to copy the concept of these transmitters, VLF radio signal, and pair that with a dive computer with custom firmware that listened for and decoded/displayed your new data.

In order to not be reinventing the wheel we would need a dive computer company to bless us with a way of flashing firmware to our computers, something that is unlikely as open source endeavors are not very profitable.

Do your computers have that I2C or whatever port on them for reading the P02 data? Because it would be totally possible to make a module that attached to the sensor and computer data ports and sends that signal wirelessly. It would be a significant amount of work and likely result in more bulk being added than a streamlined cable.

Disclaimer, I know nothing about rebreathers other than what some YouTube videos taught me.

Yeah it could be possible to create a small box that convert the signal from wireless to wired.
That would kinda be nice because these stupid cables (I look at you MOLEX !) break all the time.

 

[TheScubaPanda]

Yes, here you go: GitHub - rg422/PPS-MH8A-Transmitter: Decoding the signal used by SCUBA wireless air integration systems
I made that repository to track developments of the various bits of code related to this, I've got a rough roadmap in the readme and in the wiki I explained how to record and analyze the signal.

Got a small question, how many bits are used to transmit pressure in PSI ?

Because:
- < 1024 => 10 digits
- < 2048 => 11 digits
- < 4096 => 12 digits
- < 8192 => 13 digits

I kinda doubt the number of binary digits is variable with pressure. 12 binary digits sounds good for nearly all cases but i have read some people reporting 5000PSI being the max in this thread.

Also is the full value reported ? Or is it PSI/2 ?

 

[rg422]

@JonathanD-Panda 9 Digits as seen in the blue portion of the binary packet here: 2. Analyzing The Signal · rg422/PPS-MH8A-Transmitter Wiki

On that page is a breakdown of the packet and which segments represent what.

Full value, the psi/2 was my incorrect initial guess as I left off a bit at the end. 5000 psi is the max pressure my teric will display, even if I encode a signal with a higher value.

 

[TheScubaPanda]

@JonathanD-Panda 9 Digits as seen in the blue portion of the binary packet here: 2. Analyzing The Signal · rg422/PPS-MH8A-Transmitter Wiki

On that page is a breakdown of the packet and which segments represent what.

Full value, the psi/2 was my incorrect initial guess as I left off a bit at the end. 5000 psi is the max pressure my teric will display, even if I encode a signal with a higher value.

How do you encode "5000" with 9 digits ??? Given that 2⁹ = 512 ...
I'm confused ...

 

[rg422]

On that page the example pressure is 266, a decimal to binary converter like this gives you the 100001010 that is found in the message and visa versa.

https://www.rapidtables.com/convert/number/decimal-to-binary.html

 

[tursiops]

I kinda doubt the number of binary digits is variable with pressure. 12 binary digits sounds good for nearly all cases but i have read some people reporting 5000PSI being the max in this thread.

It is not clear to me how many bits are available for the pressure; there are 12 bits between the ID and the 4-bit battery status, so it depends on whether there are 0,1,2,3, or 4 buffer bits between the two numbers. It even depends on whether the battery status is 4 bits, since only 2 are needed. My guess is all 12 bits are used for the pressure, to keep things in 4-bit nibbles.

Note that the 5000 you saw was referring to the largest number the Teric would display, based on receiving the simulated signal, and was not something sent by the transmitter.

 

[rg422]

It is not clear to me how many bits are available for the pressure; there are 12 bits between the ID and the 4-bit battery status, so it depends on whether there are 0,1,2,3, or 4 buffer bits between the two numbers. It even depends on whether the battery status is 4 bits, since only 2 are needed. My guess is all 12 bits are used for the pressure, to keep things in 4-bit nibbles.

Note that the 5000 you saw was referring to the largest number the Teric would display, based on receiving the simulated signal, and was not something sent by the transmitter.

Your correct, the transmitter has space to send a larger number, but i imagine most computers would not display it. The only buffer bits we identified were once preceding the pressure so maybe those are dedicated to pressure as well, though the tx units are rated to 5k so no real application for sending more.

 

[tursiops]

Your correct, the transmitter has space to send a larger number, but i imagine most computers would not display it. The only buffer bits we identified were once preceding the pressure so maybe those are dedicated to pressure as well, though the tx units are rated to 5k so no real application for sending more.

But for sure you want to be able to send 3500...and that takes 12 digits, exactly how many there are between the ID nibble and the status nibble.

 

[rg422]

My bad, there's 12 or 13 available, everything following the ID until the 4 battery bits is fair game