LeeYoo
Well-known member
Hi,
My daughter asked me to design a directional hydrophone for tracking whales and dolphins. The range had to be close to 5nm (9km). Not an easy task. Most info on the net is to make omni or towing ones. Some info about underwater communication (voice). None about directional finders.
I ended up using a normal 28mm piezo disc out of a buzzer and mounted it in a 7" household funnel with small outlet.
I used a FET (2SK596) from an electret mic. capsule, and soldered that onto the disk. These fets have an inbuild protection diode and a 25meg gate resistor. And used a 2m shielded wire from a computer mic.
I cut a 25mm disc from a piece of double sided closed cell foam tape (the tape that sticks bathroom accessories to the wall) and stuck it to the ceramic part. This gives the small air space for the disk to bend.
I covered the whole back with 5min. epoxy. After hardening, I put it all in the funnel and potted the back up with more epoxy. After hardening, I used a small amount of epoxy to "varnish" the front of the disk. Avoid air bubbles here. Mounted it all to a 32mm drainpipe with the bottom 20cm bend in a 45 degree angle.
Because she wanted to use headphones, I used the good old LM386 in a standard 46db gain configuration (cap between pin 1 and 8 ). I used 1uF here to not amplify the lower frequencies. I used a single transistor amp stage between the hydrophone and the LM386 for more bandpass options. Total gain is more then 50db. It runs on a 9volt batt and draws about 5-10mA.
My question: who has done something like this before, who knows about frequency response of various sized piezo's and what effect the load impedance has on the output signal, and the effect on covering the brass with epoxy or glass or plastic, or keeping it bare. Are there better piezo shapes for directional finders. Am I missing something?
Any thoughts.
My daughter asked me to design a directional hydrophone for tracking whales and dolphins. The range had to be close to 5nm (9km). Not an easy task. Most info on the net is to make omni or towing ones. Some info about underwater communication (voice). None about directional finders.
I ended up using a normal 28mm piezo disc out of a buzzer and mounted it in a 7" household funnel with small outlet.
I used a FET (2SK596) from an electret mic. capsule, and soldered that onto the disk. These fets have an inbuild protection diode and a 25meg gate resistor. And used a 2m shielded wire from a computer mic.
I cut a 25mm disc from a piece of double sided closed cell foam tape (the tape that sticks bathroom accessories to the wall) and stuck it to the ceramic part. This gives the small air space for the disk to bend.
I covered the whole back with 5min. epoxy. After hardening, I put it all in the funnel and potted the back up with more epoxy. After hardening, I used a small amount of epoxy to "varnish" the front of the disk. Avoid air bubbles here. Mounted it all to a 32mm drainpipe with the bottom 20cm bend in a 45 degree angle.
Because she wanted to use headphones, I used the good old LM386 in a standard 46db gain configuration (cap between pin 1 and 8 ). I used 1uF here to not amplify the lower frequencies. I used a single transistor amp stage between the hydrophone and the LM386 for more bandpass options. Total gain is more then 50db. It runs on a 9volt batt and draws about 5-10mA.
My question: who has done something like this before, who knows about frequency response of various sized piezo's and what effect the load impedance has on the output signal, and the effect on covering the brass with epoxy or glass or plastic, or keeping it bare. Are there better piezo shapes for directional finders. Am I missing something?
Any thoughts.