Moodz' Awesome Gold Pulse Induction Version 3 - MAGPI V3 Project

[AhmatAhmatov1959]

Slow drift can be a symptom of two things.

The differential amp is overloaded / railed .... the voltage at the oupuf of the differential amplifier U1 should be fairly constant at around 1 to 1.5 volts. If it is closer to 0 or 2.8 volts then the amplifier is seeing an offset current due to ..

1. Leaky input capacitors ... the DC blocking caps must be high quality film caps C6 and C7. Even a very small leakage current will cause an offset DC votage that will rail the output. The integrator caps need to high quality too. Ceramic caps are way too leaky.

2. Overload input ... the samples from the integrators R13, R14, C4, C5 are overloading the input to the amplifier. If the difference between voltage inputs exceeds 150 microvolt approx then the diff amp will overload. Bad sampling windows will do this.

Hello. I assembled Magpi 3. The speaker produces a constant sound that disappears when the target is brought closer. If anyone has encountered something similar, please help. Sorry for my English

[moodz]

Hello. I assembled Magpi 3. The speaker produces a constant sound that disappears when the target is brought closer. If anyone has encountered something similar, please help. Sorry for my English

Please post some photos of the board top and bottom and we will try to assist.

[AhmatAhmatov1959]

Please post some photos of the board top and bottom and we will try to assist.

Hello. Thank you for your reply. I replaced INA125 and it worked. I buy all the parts from ALI. The metal detector has a sensitivity of 20 cm on the hand. On ferrite 15 cm. On copper getinax 50-60 cm. The gold in the photo is compressed foil, it is not an ingot. 3-4 cm. The coil is homemade with a diameter of 20 cm. I made a rope from 44 insulated wires 24 meters long and 0.17 mm in diameter wound 26 turns, left 1 meter at the beginning and 1 meter at the end. The initial meter was wrapped with 10 layers of Teflon tape and put into a heat pipe, and on top I made a screen from the last meter, additionally added 5 wires to the screen for connection to the graphite screen. The Chinese tester showed 280 mcg, 0.4 Ohm and 850 kHz together with the cable, I thought that this was a good result. If of course the tester is not lying. I have several questions for you. 1 What to do with the voltage on the coil. 2 What transistor can replace the BSP230 for higher voltage. 3 How to reduce the influence of ferrite.
I soldered a 120 pf capacitor parallel to the coil but did not notice any changes. Thank you very much for the provided project. I enjoyed making it. Before that I made a Tecoro Lobo, but after 3 unsuccessful coils I decided to do only pulse metal detectors.