Reading Wireless Air Transmitter using Arduino

[TheScubaPanda]

No that sensor would not work. Remember the 38KHz only means the frequency, cycles per second. That frequency can be transmitted via light (IR) vibration/sound (ultrasonic) or electromagnetic field (radio). Our signal is being transmitted as an electromagnetic field that induces a varying voltage in a receiving coil of wire. Same as AM/FM radio, cell phones, wifi, etc. albeit on a much much lower frequency (VLF band).

What I did was tear apart an old speaker and use the winding of wire as an antenna. For receiving and recording the samples that we used to decipher the signal I used a device built for receiving RF signals. A computer sound card, depending on the max sample rate, can also receive and transmit at 38KHz. Problem is they are quite weak for transmitting, I haven't tried it for recording but it should work fine.

Edit: Frequency isn't really "transmitted" is just a characteristic of the signal. Its the photons, EM waves, or sound waves being TXed.

Oh I see. Any idea what to use to RX / TX radio signals with an arduino ?

 

[tursiops]

Oh I see. Any idea what to use to RX / TX radio signals with an arduino ?

One way to start is here.

Software-defined radio - Wikipedia

en.wikipedia.org

 

[MadUKDiver]

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

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

There are 12 bits for the pressure. It is encoded as PSI divided by 2 so the maximum binary value 111111111111 is 4095 decimal which equates to 8190 psi.

A full breakdown of the TX format is per attached doc.

 

[Whitrzac]

I haven't been following as closlly as I should have...

Are you able to transmit a signal to the dive computer using an adrino/etc?

The idea floating around is to hook something up to the DPV that's transmitting to the perdix, setup a tank for 0-100bar and have a battery gauge on the perdix

 

[rg422]

@MadUKDiver Is it PSI/2? I thought that was just because I left out a zero at the end.

@TheScubaPanda I think the dac in most arduinos could tx the signal as it its, you'd need a beefy power amplifier to get any distance though.

@Whitrzac Yes, that would be totally possible, just a matter of writing the code, making it waterproof and choosing a balance between power output and battery life.

 

[Whitrzac]

@MadUKDiver Is it PSI/2? I thought that was just because I left out a zero at the end.

@TheScubaPanda I think the dac in most arduinos could tx the signal as it its, you'd need a beefy power amplifier to get any distance though.

@Whitrzac Yes, that would be totally possible, just a matter of writing the code, making it waterproof and choosing a balance between power output and battery life.

Wouldnt need to be waterproof, it would be inside the DPV and could be powered off the DPV batt

 

[rg422]

Wouldnt need to be waterproof, it would be inside the DPV and could be powered off the DPV batt

Should be straight forward then, if someone can help me with the Arduino code I can do everything hardware related.

 

[MadUKDiver]

@MadUKDiver Is it PSI/2? I thought that was just because I left out a zero at the end.

Yes, 12 bits and PSI/2, the least significant bit represents 2 psi.

I believe it to be as per the schema I outlined in the .doc (and amendments I uploaded to your google doc).

In your testing I had sent you some samples that flipped the next bit in the tx sequence (start of the battery status nibble) and it did not influence the pressure value you reported. You can test it again using the demo software, just type 4 bits binary into the battery status section of the demo.

 

[MadUKDiver]

@TheScubaPanda I think the dac in most arduinos could tx the signal as it its, you'd need a beefy power amplifier to get any distance though.

@Whitrzac Yes, that would be totally possible, just a matter of writing the code, making it waterproof and choosing a balance between power output and battery life.

Shouldn't need the DAC, just a port pin and bang out 38Khz square wave pulses into a suitable coil/ferrite antenna. Use the ADC to read the battery voltage and output every 5 seconds, job done. Could even set some thresholds for 'low' and 'critical' voltages.

There are many Arduino 'remote control' software examples around that would be an easy starting point for software development. Just need to change the IR transmitter diode for a coil/ferrite antenna (with maybe a transistor to beef up the current). Pulse timing will need to be changed in the software to match the M8HA values as they did not stick to the NEC protocol. Many years since I did anything with an Arduino and the few bits I've got around me are probably well out of date now.

 

[TheScubaPanda]

I have been looking around and it looks like there is absolutely no project even attempting to do RF transmission at 38 kHz or even LF.

I wanted to try have fun with the few arduinos I own. But I'm stuck at the antenna part. I can't find something that would work.

You seem to mention a coil and ferrite. How big/long the coil? How many winds?