Reading Wireless Air Transmitter using Arduino

[rg422]

Does anyone know what the low and critical thresholds are for the low voltage?
I've identified that the battery data is contained in the nibble before the checksum. at something below nominal i got (pressure)0100(checksum) instead of the usual 0000. This makes sense as different transmitters use 3.0 or 3.2 nominal batteries so it should be a relative good low or critical warning.

What voltages should I try? I seem to remember from the other day that the transmitter does not boot up over 2.5 or 6.

 

[MadUKDiver]

It works! 248 psi on id 104308 on teric.
Do you think you can add checksum calculation to your program?
Also how hard would it be to create a decoder as well as an encoder?

OMG! That's awesome.

What are you using to play the file?

I tried it on my laptop but got no response from AI on my NERD2. When I checked the audio output from my laptop on my scope it tops out at around 20 kHz so little surprise the carrier at 38 kHz has no chance. A 40 kHz sinusoidal wav aliases at 20Khz.

Already added the checksum to my program, I was going to produce 4 more wav files with single bit changes in the nibble just before the checksum but it seems you are already on the case. Hopefully one or more bit changes will cause a battery related response on your Teric.

From the Shearwater Swift manual - Battery warning levels (test with a 1mA load)

• 2.75V yellow (low) battery warning.
• 2.50V red (critical) battery warning.

 

[rg422]

OMG! That's awesome.

What are you using to play the file?

I tried it on my laptop but got no response from AI on my NERD2. When I checked the audio output from my laptop on my scope it tops out at around 20 kHz so little surprise the carrier at 38 kHz has no chance. A 40 kHz sinusoidal wav aliases at 20Khz.

Already added the checksum to my program, I was going to produce 4 more wav files with single bit changes in the nibble just before the checksum but it seems you are already on the case. Hopefully one or more bit changes will cause a battery related response on your Teric.

From the Shearwater Swift manual - Battery warning levels (test with a 1mA load)

• 2.75V yellow (low) battery warning.
• 2.50V red (critical) battery warning.

I am using a pair of cheap earbuds plugged into my computers soundcard, it claims to work upto 44khz. (I haven't checked it on my scope) Note I do need to play the signal ~10 times with the earbuds laying on the teric before it decodes it, I will soon figure out a much better way to do this.

Standby I will test those voltages and record the data and report back.

 

[MadUKDiver]

I am using a pair of cheap earbuds plugged into my computers soundcard, it claims to work upto 44khz. (I haven't checked it on my scope) Note I do need to play the signal ~10 times with the earbuds laying on the teric before it decodes it, I will soon figure out a much better way to do this.

Yep, looks like a decent soundcard is required.

I've made 4 new wav files with different battery bits set. You can download them fin a zip file here

I'm going to make some more wav with different ID's so we can test if we've got the codes for that correct. I'll upload those shortly.

 

[tursiops]

Shearwater flags Warning at 2.75V, and Critical at 2.5V. My OC1 only says "GOOD" or "LO" at some point.

Does anyone know what the low and critical thresholds are for the low voltage?
I've identified that the battery data is contained in the nibble before the checksum. at something below nominal i got (pressure)0100(checksum) instead of the usual 0000. This makes sense as different transmitters use 3.0 or 3.2 nominal batteries so it should be a relative good low or critical warning.

What voltages should I try? I seem to remember from the other day that the transmitter does not boot up over 2.5 or 6.

Already added the checksum to my program, I was going to produce 4 more wav files with single bit changes in the nibble just before the checksum but it seems you are already on the case. Hopefully one or more bit changes will cause a battery related response on your Teric.

From the Shearwater Swift manual - Battery warning levels (test with a 1mA load)

• 2.75V yellow (low) battery warning.
• 2.50V red (critical) battery warning.

I looked at the manuals for some other computers that receive the MH8A transmissions.

• Aqua-Lung i470TC just reports "GOOD" or not for battery voltage.
• Aqua-Lung i770R says LOW with a Yellow background at 2.7V, and LOW with a Red background at 2.5V.
• Sherwood Amphos 2.0 just reports GOOD or LO.

Since there are only 4 bits max that might be used for the battery status, if you are correct that the status is encode in teh 4 bits before the checksum, then it seems likely that the transmitter is not sending a voltage but rather the status...and this only needs 2 bits. Something like: 00 is voltage above 2.75, 01 is below 2.75, and 10 is below 2.5.

 

[MadUKDiver]

It works! 248 psi on id 104308 on teric.

I've made 4 more wav files with different Id's. We need to find the coding for '6' and '9'. Let's try my guesses first. You can download the files here

Let me know which ones work?

 

[rg422]

I've made 4 new wav files with different battery bits set. You can download them fin a zip file here

It worked, interestingly the teric decoded and displayed pressure for all the recordings, I got a low batt warning with 0010 and the batt text turned to red indicating critical battery with 0001

So: for batt
0000 good
0010 low
0001 Critical

 

[rg422]

I've made 4 more wav files with different Id's. We need to find the coding for '6' and '9'. Let's try my guesses first. You can download the files here

Let me know which ones work?

123789 works
123459 does not
123456 works
055872 works

Let me know if that sounds right, and go ahead and comment on the doc here your findings, I will add the battery stuff:

MH8A Transmitter Decoding

Transmitter ID: 104308 (Preamble) (Sync) (Transmitter ID) (PSI) (Battery Status) (Checksum) 364psi 0010000001101110101101001110101110000010110110000001010111 350psi 0010000001101110101101001110101110000010101111000001011111 342psi 0010000001101110101101001110101110000010101011000001011011 0...

docs.google.com

 

[MadUKDiver]

123789 works
123459 does not
123456 works
055872 works

Let me know if that sounds right, and go ahead and comment on the doc here your findings, I will add the battery stuff:

MH8A Transmitter Decoding

Transmitter ID: 104308 (Preamble) (Sync) (Transmitter ID) (PSI) (Battery Status) (Checksum) 364psi 0010000001101110101101001110101110000010110110000001010111 350psi 0010000001101110101101001110101110000010101111000001011111 342psi 0010000001101110101101001110101110000010101011000001011011 0...

docs.google.com

Excellent progress. Well done with the battery bits.

All the ID test files used the digit coding I already put in the document. The fact that 6 and 9 have worked in two test files would suggest the coding I guessed is correct. But, on that basis 123459 should also work as it was just another test with the same coding. I have no idea why it failed.

 

[rg422]

But, on that basis 123459 should also work as it was just another test with the same coding. I have no idea why it failed.

Just retested, It works, I guess I didn't put the tx in the right place when testing the first time.