Pinger 4 - A simpler design for an ultrasonic Pinger which gives an accurate 1 second pulse.

This is a simpler design which uses an external watch crystal to provide an accurate 1 second ultrasonic pulse. Battery life is at least 3 days.
The waterproof case comes from your local B & Q (Other stores are available!)
The ultrasonic transducer cable feeds through the end cap (sealed with silicone rubber tubing) and is supported by the white 3D printed part.
The LED and a piece of fibre optic can feed the light output through a pipe outlet so that you can see it more easily from outside the case.
I have done some in-water testing on my Charlie class sub. The Pinger gives a tight "torch beam" signal which helps to locate your sunk model sub. Range is at least 4m.
The Pinger was mounted externally at the stern of the sub.
The receiver is  the "simple bat detector" using the same Banggood ultrasonic transducer as the Pinger.
http://batdetector.freevar.com/

The design uses a 16f18313 pic and an external 32.768 KHz clock crystal to give an accurate 1 second pulse.
A normally closed reed switch is "hot-melted" to the back of the battery holder and can be switched off using the magnet.
Software is available here (more information forms comments in the main.c file):
https://github.com/rdforrest/Pinger-model-submarine



This shows the back of the chip socket. The clock crystal is on the right. Two 12pF ceramic capacitors for the crystal. One 0.1 uF decoupling capacitor across the power input. The components looking like resistors are small series inductors which improve the range of the ultrasonic transducer.

would an fsk modem work over a hydrophone?

In theory we could use any signalling protocol, its just the final 'carrier' that is different, and indeed hydrophone based communications exist, but as ever the catch is in the detail:
1.  data rate is slow. This is because for a simple FSK modem type link you need a number of carrier cycles to detect the data bit. For a RF based system the carrier would be 458MHz, 27MHz or what ever, whereas for a hydrophone system the carrier would be probably 30kHz to 100kHz depending on the transducer (they are often supplied as matching Tx/Rx pairs), for those of a certain age, who remebers the audio based modem of the sinclair Z80 machines?  
2. Most hydrophones are directional, so produce a narrow torch beam of signal as David says. You could design a fully gimballed transducer tracking system (like a satelite or radar tracking system) but they don't come cheap or small (fun though!). The alternative would be a multi-channel system with multiple trasnducers to cover all angles, but then they all have to be tuned to the same frequency.....
3. interference. As sound travels through water very well it means that any 'noise' will also travel, so in a body of water with other 'stuff' going on there will be a lot of accoustic noise (waves, wind, other boats, etc) This means more filtering and/or even slower data rates.

More fun to play with might be based on lasers, pick the right optical frequency and it will travel through murky water, and a multi-channel system becomes more feasible, just cover you boat will optical sensors, bit like accoustic tiles.

PS. rather than exposing the acoustic transducers to the water pressure I have seen DIY echo-sounders (some years ago) mounting the transuder inside the hull in a tube, but filling the tube with some fluid so as to transmit the sound vibrations from the transducer to the hull, but without having the transducer having the water pressure on it. They are quite brittle so going too deep could cause it to crack.

SimonH wrote:In theory we could use any signalling protocol, its just the final 'carrier' that is different, and indeed hydrophone based communications exist, but as ever the catch is in the detail:
1.  data rate is slow. This is because for a simple FSK modem type link you need a number of carrier cycles to detect the data bit. For a RF based system the carrier would be 458MHz, 27MHz or what ever, whereas for a hydrophone system the carrier would be probably 30kHz to 100kHz depending on the transducer (they are often supplied as matching Tx/Rx pairs), for those of a certain age, who remebers the audio based modem of the sinclair Z80 machines?  
2. Most hydrophones are directional, so produce a narrow torch beam of signal as David says. You could design a fully gimballed transducer tracking system (like a satelite or radar tracking system) but they don't come cheap or small (fun though!). The alternative would be a multi-channel system with multiple trasnducers to cover all angles, but then they all have to be tuned to the same frequency.....
3. interference. As sound travels through water very well it means that any 'noise' will also travel, so in a body of water with other 'stuff' going on there will be a lot of accoustic noise (waves, wind, other boats, etc) This means more filtering and/or even slower data rates.

More fun to play with might be based on lasers, pick the right optical frequency and it will travel through murky water, and a multi-channel system becomes more feasible, just cover you boat will optical sensors, bit like accoustic tiles.

PS. rather than exposing the acoustic transducers to the water pressure I have seen DIY echo-sounders (some years ago) mounting the transuder inside the hull in a tube, but filling the tube with some fluid so as to transmit the sound vibrations from the transducer to the hull, but without having the transducer having the water pressure on it. They are quite brittle so going too deep could cause it to crack.

The reason I suggested a fsk modem is they have been used on the audio channel of FPV video transmitters to send Lightweight TeleMetry protocol (LTM) one way at 2400 baud. 2400baud is slow but its still enough for dozens if readings sent every second. https://quadmeup.com/ltm-light-telemetry-protocol/
https://www.rcgroups.com/forums/showthread.php?2963807-FSK-Modem-in-RC-Obsolete-or-a-hidden-gem

I see what you are getting at, Geo. EVen low data rates would be useful for model sub telemetry!
Simon is probably correct in that it would be less good for model control.
THis discussion has opened my eyes to some new options for model subs.
David

david f wrote:I see what you are getting at, Geo.  EVen low data rates would be useful for model sub telemetry!
Simon is probably correct in that it would be less good for model control.
THis discussion has opened my eyes to some new options for model subs.
David

it probably wouldnt work at 2400 due to the noise in the water. but it would still be viable for telemetry even down at 300baud since they are getting over 10hz at 2400, 1hz update would work for your uses.