Surf pi detector-MOD

[scs-bg]

After 20 years since its appearance, the Surf Pi remains one of the best pulse induction detectors. It has two minor problems that can be easily fixed. The reason for the first is the reverse-connected diode in the transistor type 32 . It changes the smoothing of the reverse voltage in the search coil. This is important for small time delays of gating. The best option is to replace the Darlington transistor type 32 with a MOSFET IRF 9640. To work reliably, it must be controlled with a voltage greater than 6 volts. The most suitable is a direct connection to the 555 timer. The transistor driver has been changed to work in a simplified mode and controls only the creation of strobes. Another problem with the Surf Pi is the use of a speaker instead of headphones. The sound output is active during the closing of the second gating switch of the integrator. This leads to the creation of electromagnetic interference in the receiver. Interference in the power supply is also obtained. The key that modulates the sound output slightly disrupts the work of the integrator. It is differential, but there is a problem. The reason is the leakage currents in the integrated circuit CD 4066. There are four separate keys on the diagram, but in reality this is one crystal. A very good result is obtained when the sound modulator is implemented with a separate transistor. At the same time, the sound is created after the second strobe and the creation of interference is avoided. Surf Pi began to work much better. I hope everyone will like it.

[Qiaozhi]

Have a look at the Arduino Nano Pulse Induction Metal Detector Project -> Arduino Nano Pulse Induction Metal Detector Project - Published March 2021
This fixes the problems of the Surf-PI and provides better results.

[scs-bg]

Thanks for the advice. A friend made an Arduino Nano, a really good project. But these are two different detectors - digital and analog. I have seen that analog ones in practice give more even results. They show weak signals better and are more informative. I repeat that this is my opinion.

[scs-bg]

It is true that digital detectors have less detail and are not difficult to make. Analog detectors have a lot of detail and are difficult to repeat.

[Detectorist#1]

Hi scs-bg,
You are at the beginning of the design of PI detectors, but do not be discouraged - all future knowledge is ahead of you! All we started from a not very big starting point. Ask and do, ask and do!
The TIP32C transistor is not Darlington type and haven't internal diode. This is not the problem of the first variants of Surf PI detector, but it is good that you start to analyze this schematic and to start implanting of your ideas .

[scs-bg]

You correctly noticed about the transistor tip32, the mistake was mine. With the MOSET the circuit works well. As with the speaker.

[Detectorist#1]

congratulations!

[scs-bg]

Thank you!!