I'm working on an underwater flash (strobe) rig for my camera, and am trying to figure out a way to fire the flashes remotely. It seems like this should be possible with a low frequency radio transmitter.

Every time I have seen someone post about underwater radio communication (here or on other forums) the idea has been shot down because of the way that water (salt water in particular) attenuates radio signals, but air integrated dive computers are widely available and communicate wirelessly between the sensor on the tank and the computer on the diver's watch using VLF or LF signals (frequency varies by brand; I've seen as low as 5khz an as high as 200 khz, but most seem to be under 40 khz). Those are communicating more information over a greater distance than I would need for a flash trigger (I only need it to send a single piece of information ["fire"] over ~0.5m max), and they are compact and use small batteries (usually 3.7V coin batteries).

Based on that, this seems like the perfect solution to my problem, but while compact transmitter/receiver circuits are readily available for VHF, I am really struggling to find them for VLF and LF. Ideally, I'd like to be in the 160-190 kHz range, but I don't think it is critical that I am in that range. The circuit I need is very simple. The transmitter will connect to the hotshoe of the camera such that pressing the shutter completes a circuit and makes the transmitter send out a pulse, and the receiver, upon detecting that pulse, closes the circuit on the strobe, causing it to flash.

Any suggestions of where to get or how to make transmitters/receivers that will work for this would be greatly appreciated. Thanks

 

Hi! About the RF the water, and especially the salt-water allows to communicate in very shallow distances at frequencies between 50 kHz and 100 kHz. The problem there is a size of antenna. I wonder if You`ll like the kilometer size antenna there down. But, the water is well suited for a0 acoustic synchro-impulse, especially at US or IfS frequencies, as well the light, especially the laser light, especially the red color. If any doubt about Solar impact, may use the PLL like the LM567 to dechiprate the modulated signal. If tere the max deepth is less than meter or two, well works also the magnetic field, for example the pulsed type of metal seeker coil. Just push into coil some 20 A for a milisecond and magnetic pulse may travel so far as several meters.

 

I guess if you really wanted to go with RF and low KHz frequencies, a small ferrite antenna should do for a short range, but
why not use ultrasonic?

 

Here is a 125KHz transmitter and receiver module pair that might work for you. But, I haven’t used them, it appears to be a paired connection (though some sources say broadcast is supported), meaning 1:1 rather than 1:many (for more than one strobe head).

You can buy them here for about $40 a pair.

On the other hand it might be possible to adapt something like the Melexis MLX90109 chip. It’s meant to be an RFID transceiver, but it has everything you need to send and receive signals and data at 125KHz.

There is also the possibility of adapting the Atmel ATA5282 receiver and ATA5275 or ATA5795 transmitter, intended to be used in an automotive immobilizer system.

The latter two options require designing a PCB and winding or buying appropriate coils for the antenna. Not rocket science but expect some head scratching and banging as the learning curve will be steep.

 

I guess if you really wanted to go with RF and low KHz frequencies, a small ferrite antenna should do for a short range, but
why not use ultrasonic?

The TS has a separate thread discussing an ultrasonic solution.

 

The TS has a separate thread discussing an ultrasonic solution.

Sorry, I have just seen that further down the list Ya'kov.

 

Hi! About the RF the water, and especially the salt-water allows to communicate in very shallow distances at frequencies between 50 kHz and 100 kHz. The problem there is a size of antenna. I wonder if You`ll like the kilometer size antenna there down. But, the water is well suited for a0 acoustic synchro-impulse, especially at US or IfS frequencies, as well the light, especially the laser light, especially the red color. If any doubt about Solar impact, may use the PLL like the LM567 to dechiprate the modulated signal. If tere the max deepth is less than meter or two, well works also the magnetic field, for example the pulsed type of metal seeker coil. Just push into coil some 20 A for a milisecond and magnetic pulse may travel so far as several meters.

Dive computers (using VLF) are the size of a wrist watch and communicate just fine with the gauge on the tank (also not much bigger than a watch), so it clearly is possibly to do this over distances < 2m, without massive antenna.

I don't think light communication will work, because the flashes need to be movable, so maintaining a constant line of sight between sender and receiver is problematic.

Magnetic pulses are an interesting concept that I had not considered. How likely is that to interfere with other electronic equipment (i.e., the expensive camera that the sender unit is attached to, the flashes, and dive computers).

Thanks

 

Sorry all, should have mentioned the other thread looking at ultrasonic options. It is here https://forum.allaboutcircuits.com/...ter-flash-strobe-trigger.199138/#post-1890065

 

Here is a 125KHz transmitter and receiver module pair that might work for you. But, I haven’t used them, it appears to be a paired connection (though some sources say broadcast is supported), meaning 1:1 rather than 1:many (for more than one strobe head).

You can buy them here for about $40 a pair.

On the other hand it might be possible to adapt something like the Melexis MLX90109 chip. It’s meant to be an RFID transceiver, but it has everything you need to send and receive signals and data at 125KHz.

There is also the possibility of adapting the Atmel ATA5282 receiver and ATA5275 or ATA5795 transmitter, intended to be used in an automotive immobilizer system.

The latter two options require designing a PCB and winding or buying appropriate coils for the antenna. Not rocket science but expect some head scratching and banging as the learning curve will be steep.

Thanks, those seem like intriguing options. I'll look into them