Need to ID this detector found at a Flea Market

[Dinamo581]

First of all thank you guys, I was scrolling trough these 70s 80s 90s magazines and I started to get really nostalgic...

Indeed, The Magnum built is interesting and it seems that lots of time was put to make it, whomever made it had some good soldering skills and knowledge. Everything is nice and clean made, at first I though was an early comercial made small production.

Best regards
M.

[Aleks85]

There is such information
https://drive.google.com/drive/folde...xWmtyN6dgZ0tMs

[pito]

Magnum
Does someone knows how DISCRIMINATION is working in this circuit ?

[Aleks85]

The discrimination level adjustment is designed to set the criterion for determining the usefulness or uselessness of a detected metal object by the device. This parameter is set and makes sense only in DISCR (discrimination) mode.
So, if the regulator is set to the far left clockwise position (All metals), then almost all metal objects detected by the Metal Detector in DISCR mode (both non-ferrous metals and iron, except for relatively small objects made of iron and hot stones),they will be identified as useful. In this case, a short finished beep is heard, the indicator arrow deviates to the right from "0". If the position of the regulator is vertical (approximately 4-6), then small ferromagnetic objects, beer corks, nails, fragments, iron wire, rust, hot stones, small pieces of foil and similar debris that is of no interest will be perceived by the device as useless (deviation of the indicator arrow to the left and torn or "fading" like the sound of a string signal).However, all other objects made of non-ferrous metals (coins, military and historical relics, others, as well as relatively large objects made of iron) with this position of the regulator will be perceived as useful: the deviation of the indicator arrow to the right and a short, finished beep. If the position of the regulator is further changed clockwise (up to 7), large foil and beer tongues will first be indicated as useless (cut off), while other non-ferrous metal objects (including coins, military and historical relics) and large iron objects will be perceived as useful. In the extreme right position, all objects are perceived by the device as useless – complete (maximum) discrimination.The recommended position of the regulator ("4.5 – 5.5") is the most optimal position in which small pieces of foil and iron debris are cut off. When searching in heavily littered areas of the soil (for example, on beaches), it is recommended to set the level of discrimination to position 5-6. In the case of searches in places whose soil is free from abundant industrial debris (beer corks, cigarette and other foil, aluminum wire, etc.), it is recommended not to abuse the increase in the level of discrimination, and work in 3-4 mode.It should be remembered that an increase in the level of discrimination leads to a decrease in the depth of detection of the same object, all other things being equal. So, although a copper coin will give an equally clear useful signal in DISCR mode at a discrimination level from 1 to 6.5, but at a discrimination level of "1" the depth of detection of the same coin in the ground will be higher than at a discrimination level of "6.5".
Here is all the information that is available on Magnum:
https://disk.yandex.ru/d/F_Jev32ra1Qc2Q

[Aleks85]

This is what the DISC controller looks like

[Carl-NC]

Does someone knows how DISCRIMINATION is working in this circuit ?

It's done by shifting the demodulator phase. Notice that a Mode switch selects Ground, Disc, or Beach mode. They all work the same way by shifting the demod phase. The Ground mode sets the demod phase so that ground produces a null, everything above ground (basically any metal) produces a positive response. The DIsc mode sets the demod phase so that at a certain point a particular target (say, a pull tab) produces a null and everything below that target (iron, foil) produces a negative signal and everything above it (copper & silver coins) produces a positive signal. Beach mode sets the demod phase so that salt water produces a null, it's basically Disc mode just for salt water.

[pito]

@Aleks85

Did you build that detector, what is sensitivity to coin ?
Thanks for the link.

[pito]

@Carl-NC
Thanks for explanation.
everything above ground (basically any metal) produces a positive response. = not clear, I thought that Ground and Beach mode will produce positive signal for iron and negative for copper. We have a null when signal phase is 90 deg shifted compared to switching pulses.

Let say; iron gives +20 deg phase shift and copper gives - 15 deg shift,
that will produce + 20 mV or - 15mV , while no metal gives 0mV, so discrimination is present.

[Aleks85]

I made this metal detector and used it in 2006 or 2007, I haven't had it for a long time, the finds with it were good.

[Altra]

I'm curious on the function of the cd4007? Is it being used as an analog switch, analog mixer or a signal blanker?

This would make a good project to modernize using dual opamps and smaller electrolytic etc

[pito]

analog switch, = it is a switch = synchronous detector

[Altra]

Thanks

[pito]

today = SN74LVC1G3157

[Carl-NC]

everything above ground (basically any metal) produces a positive response. = not clear, I thought that Ground and Beach mode will produce positive signal for iron and negative for copper. We have a null when signal phase is 90 deg shifted compared to switching pulses.

Ground mode is an all-metal mode. Ground phase is about 0° and so the only thing you get is the R signal, making everything else a positive signal. In Beach mode, all you get is an X signal so ferrous is negative and non-ferrous is positive. In Disc mode you are moving the null point around; if it is set to pulltab then nail/salt/foil is negative and copper/silver coins are positive. You can design the detector to invert these polarities (I don't know what the Magnum does) but the physics is the same.

[pito]

making everything else a positive signal. = And what is not everything else? It is gives a negative signal?
In Beach mode, all you get is an X signal so ferrous is negative and non-ferrous is positive = my theory from post #23 it is ok ?