ARMD (ARMRADIO based Metal Detector) VLF IB PROJECT

[moodz]

And why is it that the classic full H-bridge is not used in branded metal detectors, and in homemade ones too? Two assemblies of P/N mosfets (for example, IRF7105, 7309), one TC4428 type driver are enough. This, of course, applies to the VLF, for a pulsed metal detector, such a bridge circuit is not suitable. What is the advantage of the TX cascade on 6 transistors over the TX cascade on 4 transistors?
With a TX cascade of 4 transistors, the metal detector can use a lower voltage (3-9V) TX and a coil with fewer turns. The TX coil with low inductance will be less affected by the Earth's magnetic field, which in turn will provide a more stable phase characteristic of the TX circuit

There are one or two metaldetectors with H bridges though more complex than 4 transistors and a gate driver as you put it.

The short answer is that the 6 transistor configuration recycles the flyback energy on each pulse and uses considerably less energy than a conventional H bridge.
The CCPI can run off as little as 1.8 volts with 2 amps peak to peak in the coil whilst only using 1.5 watts.
Out of the 6 transistors (mosfets ) you only need 2 high voltage units not 4 like a H bridge ... these are the expensive devices.
Its a bipolar transmitter and RX so earths field is inherantly cancelled during RX sampling.

[JoyJo]

Fine. I almost got it. "6 transistors" are more economical in terms of money and have a higher efficiency.
And if you set the supply voltage of the TX cascade to 2.5-9V. Which mosfets are worth paying attention to? Does the CCPI support operational voltage regulation: at high frequencies, increase the TX voltage to increase the field strength of the TX coil, at low frequencies, reduce the TX voltage to reduce the current in the coil.

[moodz]

Fine. I almost got it. "6 transistors" are more economical in terms of money and have a higher efficiency.
And if you set the supply voltage of the TX cascade to 2.5-9V. Which mosfets are worth paying attention to? Does the CCPI support operational voltage regulation: at high frequencies, increase the TX voltage to increase the field strength of the TX coil, at low frequencies, reduce the TX voltage to reduce the current in the coil.

As you increase the supply voltage the current will increase and the probability of MOSFET avalanche will increase. I use 3.3 volts for 2 amps peak to peak and the flyback is around 800 to 1200 volts. I have found silicon carbide MOSFETs give good results.

[JoyJo]

I understand that it will not work to assemble this TX cascade on SMD components, such as soic. But the truуhole element is very bulky.

[moodz]

I understand that it will not work to assemble this TX cascade on SMD components, such as soic. But the truуhole element is very bulky.

I am not sure why you think that ... SMD works ok.

[JoyJo]

I just remember the photo of your PI detector layout. You used "big" tools. It is justified for a PI detcutor to use a "reverse stroke". But for the VLF, how appropriate is the ccpi?

[moodz]

The through hole parts are used for prototypes. SMD works fine. The CCPI generates pulse or sinewave.

[moodz]

Update to make it clear how we switch the detector from PI to VLF mode.....

[moodz]

...just to let you know that things are still happening with the VLF PI.

I found this ARM development platform that puts all the DSP together by simply drawing it and then runs it live in the ARM processor .... less than 5 minutes to generate the core binary for the VLF detector signal chain and have it actually running on the hardware in real time - but still able to debug and change settings.

[moodz]

Setting the input to -52 dbmV and RX frequency to 13 kHZ ( TX is 11 kHz ) we get an RX magnitude of 40 dbmv and correct phase rotation from +/- PI ... AKA 3.14 ( due to the difference frequency btn TX and RX ).
This is running in real hardware ... so its working.

[Gunghouk]

Is this Audio Weaver Designer?

[moodz]

Is this Audio Weaver Designer?

Well spotted ... it is indeed.

The only fly in the ointment is that it is not open source. It uses Matlab in the backend and the DSP is highly optimised.

[Gunghouk]

So this project won't run in the free standard version without Matlab?
What DSP eval board are you using?

[moodz]

AudioWeaver uses Matlab internally in the Free version so you dont need it separately ( downloads a core during install ).

I am using STM32F407 Disco board.

[Gunghouk]

Thanks