I am working on hacking a sonar for some time now (long story here:https://forum.arduino.cc/t/interfacing-fish-finder-take-2/679629/57 ) and finally have a tested working solution but there is one missing piece that I need help on: the tuned inductor. At the moment, I use the inductor that is embedded on the hacked device and there is no way to tell what characteristic it have and I destroyed it while trying to unsolder it from the board. I want to select and buy one but don’t know where to start and would be very happy to have some help with this.
To work and from what I understand, the inductor need to transform a 5v input into a 70 volts p-p output. The input frequency generate by PWM match the output frequency that is : 200 khz. The resonant factor Q should be about 48 based on the transducer characteristic I have found so far. The diode + resistor and capacitor in the top left part of the schematic have a charging time constant of about 0.2 sec and keep the input inductor voltage high between pulse. Schematic below.
edit: since it was destroyed anyway, I unwinded the inductor. The transducer side have 355 turns, exactly 2.5m long of thin wire coil (about 0.05mm). The variable side was made of two 15 cm long wire (0.1 mm) and they each have 15 turns for a total of 30 turns. It was winded on the exterior of the other coil.