Differential TX driver for TDI?

[eduardo1979]

Hello everyone.
I have an idea that I find quite interesting and I need help to implement it.
I have a Whites TDI SL metal detector and I'd like to add an improvement to the transmission circuit. I'd like to implement the differential driver shown below in Carl's ITMD3 book. I'm aware that the TDI driver only has one output, but I'd like to be able to convert this output into two outputs, in order to control two IRF740 MOSFETs, as in the attached schematic. I've built a homemade 6" differential inductor to use in this experiment. I don't know if there's any kind of commercially available driver with one input and two outputs that are out of phase with each other, or if not, I'd prefer to build one myself, but I need a schematic for it. I'm sure Carl or one of the experts could help me.
Thanks in advance.

[JoyJo]

And what is the main advantage of such a TH and what will the TX coil look like? Is it for pulse detectors or IВ?

[eduardo1979]

I found something in one of Eric's posts, but I don't know if that would help with the cancellation of EFE.

[eduardo1979]

And what is the main advantage of such a TH and what will the TX coil look like? Is it for pulse detectors or IВ?

It's for TDI, which is a PI detector. The idea I'm proposing would help cancel the Earth's magnetic field, and I think it could be applied to any PI metal detector. For now, we'd have to hear the opinions of the experts.

[Altra]

It's basically a BiPolar transmitter. If you demodulate the signal alternating between +pulse and -pulse the earths field is eliminated. See the Bipolar circuit in ITMD3 you could use the the same differential pre-amp and sample timings.

Two other examples of this Tx are the Whites mine detector and a prototype called the Manta.


https://www.geotech1.com/forums/foru...metal-detector

[eduardo1979]

Hi Altra. I completely understand what you mean, but what I want to do is use this bipolar system in the TDI SL. The TDI SL microcontroller provides one PWM output to control the gate driver of the IRF740S, and I need two outputs to control two IRF740S transistors. Basically, I want to create two outputs from one, with square wave signals out of phase with each other, so that the two N-channel MOSFETs don't turn on or off simultaneously. The operation would be the same as the AF108, in push-push mode. In this case, the TDI would function normally, but with bipolar transmission and a differential coil. To summarize: I just need a kind of half-bridge MOSFET gate driver with only one input and two outputs out of phase with each other, and those outputs must be compatible with N-channel MOSFET transistors. I don't want to use microcontrollers, only integrated circuits, since I'm not good at programming.

[GeoMax]

Hi eduardo1979,

are you looking for something like this circuit?

[GeoMax]

I found something in one of Eric's posts, but I don't know if that would help with the cancellation of EFE.

Do you have the complete GoldQuest schematic?

[eduardo1979]

Hi Geomax. I don't have the complete Goldquest schematic. The schematic you posted isn't the solution I'm looking for. Thanks anyway.

[JoyJo]

Are you looking for such a driver?

[Carl-NC]

I found something in one of Eric's posts, but I don't know if that would help with the cancellation of EFE.

This schematic shows that a split coil is driven at the same time with the same pulse, and is then combined into a single receive signal. It won't do what you want.

To do what you want requires generating an independent TX pulse for a second driver. That means modifying the PIC code, which means you will need to replicate the existing PIC code. That's not too hard because it mostly just generates timing pulses, and there are a few unused pins available. Then, the second TX coil output will need to drive the (+) side of the preamp (via a clamp) which, fortunately, has a convenient resistor (R13) that can be removed. Finally, you will need to add new timing pulses for the sampling switches to grab the samples for the new negative TX pulse.

None of this is impossible and is quite doable. You will need to make a small daughterboard for the new components and write new firmware. Also fortunately, the coil connector has 5 pins so assigning one to the new TX phase isn't hard, but it might be hard to maintain compatibility with stock coils.

[GeoMax]

Hi Carl,

What do you think of the small circuit I posted in post #7? I think it's suitable for generating a double-pulse signal from a single pulse, as needed by eduardo1979. The left part is an oscillator that can be driven by the TDI output pin, and the other parts generate the two pulses (+/-) to drive the two MOSFETs of your circuit from the ITMD3 book.

[pechkata]

Here it is - a little but from the heart.

[eduardo1979]

Here it is - a little but from the heart.

Thank you very much, Pechkata, for your contribution.
You are very kind, but what I need is something completely different. I have Carl's ITMD3 book; I bought it when Carl released it, and I have also successfully built the Bipolar PI detector. I want to improve my TDI detector. I want to obtain bipolar pulses from unipolar pulses, since the TDI only generates one monopolar pulse, and from this pulse, I want to generate another pulse to control two IRF740s. I appreciate everyone who tried to help me.

[pechkata]

Hello Eduardo.
You can't make two impulses out of one impulse.
Karl has already written on this topic.