Reading Wireless Air Transmitter using Arduino

[kelemvor]

I've got a couple different transmitters. I've got the scubapro Galileo transmitters, and the Ratio iX3M transmitters. Disassembling them and gaining access to the PCB is trivial. You have to do that every time you change the battery and o-ring as there's only the one compartment. There is a clear conformal coating on the PCB. Manufacturers would be fools not to include one.

Spectrum analyzers have become shockingly inexpensive. I ordered one from Amazon for $70. I'm sure it's not the best ever made but should be sufficient to complete a frequency sweep assuming the thing transmits above 100khz. That's pretty low, not too far from audible (to hoomanz).

 

[Robbyg]

I've got a couple different transmitters. I've got the scubapro Galileo transmitters, and the Ratio iX3M transmitters. Disassembling them and gaining access to the PCB is trivial. You have to do that every time you change the battery and o-ring as there's only the one compartment. There is a clear conformal coating on the PCB. Manufacturers would be fools not to include one.

Spectrum analyzers have become shockingly inexpensive. I ordered one from Amazon for $70. I'm sure it's not the best ever made but should be sufficient to complete a frequency sweep assuming the thing transmits above 100khz. That's pretty low, not too far from audible (to hoomanz).

NO, be careful the frequency is not above 100Khz it's below that!
The Pelagic is 38Khz and as far as I know all of them fall somewhere between 30Khz and 50Khz. You need a SA that can go down into those frequency ranges.

 

[kelemvor]

I opened my scubapro tx. You can see the antenna housing (black tube). It's a coil type antenna, much like the old 100 in 1 project kits carried. The Ratio tx has a clear case, and the antenna is exposed. Standard copper coil.

Here are photos of the chips on the scubapro. I haven't identified them yet.
Chip1
MSP430
F4250
TI 14K A
CVX8 G4
Chip2
A13
Chip3
ON AC
125
PJUU
Chip4
S04A

Also, there are two sets of JTAG pads on the board.

 

[kelemvor]

Chip1 is a TI part: MSP430F4250
8-MHz Sensing MCU with 1 16-bit Sigma-Delta ADC, 12-bit DAC, 56-segment LCD, 16KB Flash, 256B RAM
Data Sheet: https://www.ti.com/lit/gpn/msp430f4250
User Guide: https://www.ti.com/lit/pdf/slau056
Development Guide: https://www.ti.com/lit/pdf/slau840

 

[njmorrell]

I wonder how those Suunto transmitters dealt with multiple divers transmitting close to one another? When you look at the Pelagic signal structure their is a first section of the pulse that remains the same and I think its safe to assume that is the serial number and then the last 1/4 of the pulse have a lot of shifting happening. I assume that is the last tones for the least significant digits of the Air Pressure.

I guess they had some kind of identifier or maybe just signal strength. You had to hold the computer next to the transmitter to get it to start working (a bit like the early heart monitors from Polar), it was all a bit problematical because sometimes it would just refuse to work.

The problem with Suunto is that they are quite secretive about their technology.

I think these days the Pelagic Systems transmitters are used by several different dive computers including Shearwater which all handle multiple transmitters. I have no idea who made the Suunto transmitters.

The FCC ID MH8A just says low power below 1705kHz, not much help.

Nick.

 

[kelemvor]

Chip2: = Microchip 24AA01 in 5 lead SOT-23 package
I2C™ Serial EEPROM
Data sheet: http://ww1.microchip.com/downloads/en/DeviceDoc/I2C Serial EE Family Data Sheet 21930C.pdf
Size: 1Kb
Vcc: 1.7-5.5
Clock max: 400kHz (100kHz if vcc<2.5v)
Page size: 8 bytes
Temp Range: I (-40c to +85c)

 

[kelemvor]

Chip3: ON Semiconductor MC74AC125
Quad 3-state Buffer with Low Enable High−Performance Silicon−Gate CMOS
Datasheet: https://www.onsemi.com/pub/Collateral/MC74AC125-D.PDF

Chip4: TI LM2665 Switched Capacitor Voltage Converter (160kHz)
Datasheet: https://www.ti.com/lit/ds/symlink/lm2665.pdf?ts=1613752981097

 

[kelemvor]

This is interesting, I've never seen a ribbon cable attached this way. It appears the cable was attached during PCB manufacture! Normally they'd be soldered on or would use a connector. How strange!



Also: No conformal coating. How disappointing, scubapro.

 

[tursiops]

Spectrum analyzers have become shockingly inexpensive. I ordered one from Amazon for $70. I'm sure it's not the best ever made but should be sufficient to complete a frequency sweep assuming the thing transmits above 100khz. That's pretty low, not too far from audible (to hoomanz).

If you bought that TinySA, it will go below 100kHz but with reduced sensitivity.
Your last sentence implies humans could hear it if it were a bit lower in frequency.....but humans don't hear RF.

 

[kelemvor]

If you bought that TinySA, it will go below 100kHz but with reduced sensitivity.

It goes down to 10khz well enough for this project. Here's a video where a guy tests it below 100kHz and gets totally usable results.