Metal detector test circuits for testing the electronics.

[GeoMax]

Hello forum!
Does anyone have a circuit to generate or simulate signals for "poor soil" or "black sand" for testing purposes? Or perhaps an idea how to set up such a test circuit? What would such signals look like? Perhaps something like a pink or white noise generator? Or perhaps a spike generator? I once saw a video from Whites Electronics that sparked my questions. In it, a signal was applied to the circuit to test or calibrate it.

[Carl-NC]

To balance the demods on the TDI, a 3Hz signal was injected into the preamp. But this was not a ground signal.

The best way to create a ground signal is to use ground targets. Red brick will often work well.

[N@SKO]

What type of signal is 3 hertz? Sine wave? Can you link to the video?

[kt315]

Red brick will often work well.

put red brick in salty water and keep long. brick must be wet.

[Carl-NC]

Sine wave. I don't know of any video.

[bbsailor]

Hello forum!
Does anyone have a circuit to generate or simulate signals for "poor soil" or "black sand" for testing purposes? Or perhaps an idea how to set up such a test circuit? What would such signals look like? Perhaps something like a pink or white noise generator? Or perhaps a spike generator? I once saw a video from Whites Electronics that sparked my questions. In it, a signal was applied to the circuit to test or calibrate it.

This may not be a direct answer to your question about black sand but it will be an alternative that works.

Black sand on the beach can be either organic or magnetic. I placed a magnet in a small plastic bag with a string attached to the plastic bag. When I came upon black sand at the Jersey Shore, I would throw the plastic bag and magnet on the black sand. If the sand were magnetic, the sand would attach to the plastic bag near the magnet indicating that it is magnetic sand. Then, I would slide the magnet in the plastic bag to have any attached black sand fall off the bag.

This is not an electronic way to identify black sand but it is inexpensive to make and it works.

Joseph J. Rogowski

[algan]

To balance the demods on the TDI, a 3Hz signal was injected into the preamp. But this was not a ground signal.

.

Hi Carl, how exactly is this setting done? I assume the supplied sine signal should be the same at the outputs of the integrals or is it not?

[Carl-NC]

The TDI had balance adjustment trimmers for each demod (VR11 & VR12). You would inject a 3 Hz signal into the preamp and adjust these trimmers for a minimum demod signal. This has nothing to do with test methods for bad ground, I only mentioned it because it was likely the video GeoMax was referring to. It is a test specific only to the TDI.

[algan]

Hi, GeoMax
can you upload a link to the video you mentioned. Thank you.

[N@SKO]

The TDI had balance adjustment trimmers for each demod (VR11 & VR12). You would inject a 3 Hz signal into the preamp and adjust these trimmers for a minimum demod signal. This has nothing to do with test methods for bad ground, I only mentioned it because it was likely the video GeoMax was referring to. It is a test specific only to the TDI.

Thanks for help Carl.I want to use this method to set sd2200 demodulator.I think will work on this detector

[GeoMax]

Here are the video links.
Part 1
White's Electronics Factory Tour

Part 2
White's Electronics Tour Part 2.mpg

[algan]

Hello Carl-, can you tell me exactly how this adjustment is done, what voltage should the sine wave be and with the adjustment of the trimmers should it become flat or is a minimum of the sine wave at the outputs sought?

[Carl-NC]

I don't recall the voltage, basically it needs to be as large as possible without overloading the preamp. The trimmers are adjusted for minimal demod output variation.