Hi 
I have a difficult question, hope you can help me…
I want to connect my Raspberry 3 with a transducer (P66 from Airmar should be NMEA 0183) the transducer cable (C47-C1225) has 5 wires: Blue: Positve (Depth), Bare: Shield, Black: Negative (Depth), Brown: Thermistor(Temperatur), White: Thermistor (Temperatur). http://www.gemeco.com/custom/wiring/91_674.pdf
Would it be possible to connect the transducer cable to a breadboard and a 4 Bi-directional level shifter and then via USB to NMEA adaptor (http://digitalyacht.com.au/product/adaptateur-nmea-usb/) to the Raspberry Pi?
Thank you for any ideas!
Hi Katharina,
This is a pretty tough problem you got on your hands here!
I really need to know a little bit more about the P66 to give you a straight answer. Is there a datasheet available for it? Something with specific voltages? From the Diagram you’ve shown me it looks like it uses analog signals rather than digital. Are you sure that this is a self contained unit? By that I mean do you know that you just power it up and it starts to sense? It could be dependent on a computer connected to it to control the sensor.
I think the easiest way to work this out would be to connect it to an Arduino, and then have the Arduino interpret the data and send it to a Raspberry Pi over USB. You can cut out the middle man here, but Arduino devices excel with interacting with hardware, and are a better choice for connecting your transducer to.
I assume that it works off 12V, and I don’t know how many amps it draws so I cant do this calculation for you, but Voltage (V) = Current (I) * Resistance ®. If you put an appropriately sized resistor in your signal line you can drop the voltage from 12V to the 5V that can be safely read by a Raspberry Pi.
I hope that helps! See if you can dig up some more info on the P66!
Hi Stephan,
thanks for your answer!!!
The data sheet of the P66 is this one http://www.airmar.com/uploads/brochures/p66.pdf , maybe this could be helpful, too http://www.ohmex.com/p66.pdf http://www.airmartechnology.com/uploads/InstallGuide/17-247-03.pdf
The transducer is a dual beam with 50 and 200kHz, it can measure the depth and the water temperature…when it works. I can’t find something about the required voltage 
I guess you’re right the transducer is using analog signals. So the arduino would be good to convert the signals into digital for the Raspberry Pi as well?
I am not sure if I got it right…I thougt the Pi would be already the computer… so you’re assuming I need a NMEA to USB cable an arduino, a raspberry pi, a normal USB cable and also “a real” computer?
Katharina,
I had found that p66 brochure, it doesn’t give any real info about how the device works. Proprietary devices like this often aren’t forthcoming about how they work, so it may take some testing to figure it out. If you supply the incorrect voltage it will break.
I’m not sure what your goal is for this project. A Raspberry Pi has no analog inputs, so you need to convert the signals from the sensor to be readable by the Pi (without a full datasheet I can’t promise that it doesn’t use digital signals).
An Arduino is a microcontroller, you can program it to read the analog outputs of your sensor and send that data to a Pi over USB. If you just want to display this info on a simple screen you could do it all on the Arduino.
You will not need a NMEA to USB cable.
