How to Read FishFinder Transducer data?

[Aurentiaco]

Hello I am trying to understand that how can I read the data ? Which kind of filters or amplifiers do I need for that transducer. I connect my Garmin GT20-TM to the oscilloscope to understand which kind of data does it produces because I couldn't find any kind of datasheets or pinout information online. The only information that I found by myself is that I cut the wire and look inside I saw 3 cables one red one black and one white.
Than I make the connection red wire as voltage input black as output white as signal try to see the data on oscilloscope. This is the data that I take without the connection the I connect power supply but the signal does not change. Does anybody know something about it.
First I gave 18 volt and than 12 volt.
Than I connect it to the signal generator and gave 200khz and 83khz for test but I couldn't understand the output that I take and should I gave rectangle wave or sinus wave. Can anybody help me about this problem?

[CaptDon]

I have no idea which transducer you have. Do yo understand that with 99.9% of transducers the head unit sends a huge 100vpp pulse at the design frequency of the transducer, perhaps about 10 cycles of 200KHz and then the head unit goes into the 'listen' mode and amplifies and displays the return echos. Normal transducers don't use steady voltage from a power supply and also don't use a steady tone from a signal generator. The transducer is simply the peizo ultrasonic resonant equivalent of a radar antenna and just like a radar antenna it produces no actual data. it simply emits and receives pulses of a certain frequency and duration.

[jpanhalt]

That scope can do fast Fourier transform ((FFT).  Have you looked at the signal using that?  This link (there are several others) may give you an idea what to look for: https://www.bdoutdoors.com/forums/threads/two-transducers.795749/

[Mechatrommer]

i have garmin striker and echomap for experimenting, both barely used try to understand how to decode the signal requires me to read a thesis or theory that i dont understand, probably implemented in a fpga.. hope there is light in this thread. not really helpful is it?

[Aurentiaco]

I have no idea which transducer you have. Do yo understand that with 99.9% of transducers the head unit sends a huge 100vpp pulse at the design frequency of the transducer, perhaps about 10 cycles of 200KHz and then the head unit goes into the 'listen' mode and amplifies and displays the return echos. Normal transducers don't use steady voltage from a power supply and also don't use a steady tone from a signal generator. The transducer is simply the peizo ultrasonic resonant equivalent of a radar antenna and just like a radar antenna it produces no actual data. it simply emits and receives pulses of a certain frequency and duration.

Thanks for your reply. I am using Garmin GT20-TM transducer but also I have Humminbird XNT 9 HW T Transducer. Do you know any analog front end circiutry to handle these signals in listen mode ?

[Aurentiaco]

i have garmin striker and echomap for experimenting, both barely used try to understand how to decode the signal requires me to read a thesis or theory that i dont understand, probably implemented in a fpga.. hope there is light in this thread. not really helpful is it?

Thanks anyway but do you have their circiutry photo for striker and also echomap maybe that can help a little bit to understand. Did you teardown them for testing?

[Aurentiaco]

That scope can do fast Fourier transform ((FFT).  Have you looked at the signal using that?  This link (there are several others) may give you an idea what to look for: https://www.bdoutdoors.com/forums/threads/two-transducers.795749/

Thanks for your reply I think my scope does not do FFT but I am going to check it again and also I am going to check that link you provide.

[Mechatrommer]

i have garmin striker and echomap for experimenting, both barely used try to understand how to decode the signal requires me to read a thesis or theory that i dont understand, probably implemented in a fpga.. hope there is light in this thread. not really helpful is it?

Thanks anyway but do you have their circiutry photo for striker and also echomap maybe that can help a little bit to understand. Did you teardown them for testing?

attached is striker 4CV (Garmin GT20-TM transducer iirc but not shown).. high tech stuff, probably fpga under the tin can.... the echomap i havent dismantle, probably the same or much more complex... iirc you need to read up how lidar works.. for 2d or 3d transducer.. for 1d, i guess you just measure time of flight of returned echoes, i thought buying cheap hung low fish finder but i dont have much time allocated for this subject,

[jpanhalt]

My comment was based just on the advertising:(attached)

Check the Math button.

[CaptDon]

You notice how shielded the front ends are?? Distant echo reflections are very weak so all amplifier circuitry must be low noise. Low noise opamps with a GBP of around 10MHz would be a good start but limit the stage gain to about 10 to 20 Db per stage due to GBP limitations. Once you have enough gain then the units generally hit a comparator circuit who's output generally indicates 1=Echo present, 0=No Echo Detected. To reduce noise the amplifier circuits should include bandpass filters centered on the transducer's resonant frequency (200KHz?).

[Aurentiaco]

My comment was based just on the advertising:(attached)

Check the Math button.

Yes you are right thank you I forgot the quote again. I found it when I checked.

[Aurentiaco]

You notice how shielded the front ends are?? Distant echo reflections are very weak so all amplifier circuitry must be low noise. Low noise opamps with a GBP of around 10MHz would be a good start but limit the stage gain to about 10 to 20 Db per stage due to GBP limitations. Once you have enough gain then the units generally hit a comparator circuit who's output generally indicates 1=Echo present, 0=No Echo Detected. To reduce noise the amplifier circuits should include bandpass filters centered on the transducer's resonant frequency (200KHz?).

Again thanks a lot. I have couple more questions. I need a mathematical model and hardware for that and how can I convert signal to data? Because in this transducer it measures temperature and distance. If you know can you give more information?

[jpanhalt]

I suspect converting the raw data to digital and display will be complicated and may involve some relatively proprietary software.  If you get the FFT, you might wave a solid object at a suitable distance from the sensor and see how it changes.