ib metal detector

[lucifer]

Where is the circuit and schematic ?

In the first post, or here: http://md04.narod.ru/An50/Anker50.GIF

[OLDMAN621]

Where is the circuit and schematic ?

[lucifer]

This schematic is a New year gift for all hobbyists. Basic idea is to get maximum results at minimum cost and at great repeatability.

General technical characteristics of "Anker-50"
================================================
Principle of operation - induction balance
Number of channels - 3
Maximum sensitivity in air - 50 cm for a small USSR coin
120 cm for plate with diameter 22cm
250cm for large objects
Current consumption - about 200mA in silent mode
Power supply - battery 12V, 1.3Ah
Search mode - dynamic
Indication - dual tone with ability to reject iron objects
Coil size - 25cm
Coil type - coaxial-planar (Spider)

Short description of schematic
==================================
Oscillator
DA1,VT1,VT2 are the basic parts of power oscillator using series resonance. Capacitor C4 and coil L1 form a circuit that determines the oscillation frequency of generator. Resistor R1 helps to remove the feedback signal. R3 sets the mode, LEDs Led1 and Led2 form a circuit for stabilizing the work of oscillator. Power supply of oscillator 9V is regulated with SR1.

Phase shifters
They are used to form control signals for the synchronous detector and compensating signal of residual coil unbalancing.
Harmonic signal is sampled differentially from the resistor R1 and then is amplified by DA2.1. Resistors R6 R7 determine the the signal amplitude. DA2.4 creates a 90 degree phase shifter. Resistor R14 sets the desired phase shift of the stage. DA2.2 and DA2.3 are 180 degree inverters. In this way at output of DA2.1 we have 0 degrees, at DA2.4 - 90 degrees, at DA2.2 - 180 degrees, at DA2.3 - 270 degrees.

Coil
Connecting receive and compensating coils in series together with capacitor C11 form a circuit tuned exactly to resonate with the oscillator. DA13 is a buffer stage that removes the negative effect of cables connecting the coil and electric circuit.

Input amplifier
Made with the inverting opamp DA3.1. The signal from the sensor is added to the compensating signals from resistors R19 R20 and fed to the inverting input DA3.1. Resistor R21 determines the gain of the amplifier.


Ground balance phase shifter
Realized with DA3.2, resistor R24 produces a rough adjustment, R25 is for fine adjustment.

Synchronous detector
Consists of analog switches DA6 DA7 and amplifiers DA8.1 - DA8.3. Antiphase synchronous detector control signals are generated by comparators DA4 DA5. The top two channels are used for ground compensation and detecting the presence of metal, the bottom - determines the type of metal (ferrous - non ferrous)

Channel amplifiers
They are implemented with DA9 and DA10, the feedback circuit includes a ground channel compensation diode limiters to protect the opamp and ensures rapid recovery after overload.

Transistors VT1 and VT2 form an analog version of logical element "AND" - this circuit transfers a signal to the output only if both signal channels are high. This happens only if under the coil a metal object is present. In the case of stone, approaching the sensor to the ground or sensor shock, one channel goes up, and the other - down and at the output (emitter VT2) signal is suppressed. The third channel amplifier controls the multiplexer at which inputs (13,14) come signals of high and low tones, which are formed from the counter DA12 from signal generator.
When a ferrous or non-ferrous metal is present, at hte output of the comparator DA10.2 low or high tone signal appears and an audio indication occurs.

Sound control circuit
When implementing circuit for sound control a specific problem occurs. Its essense lies in the fact that in order to take a decision to activate the first or the second audio channel, the third audio channel has to trigger before the appearance of a signal controlling the sound volume (emitter of VT2). For this quick response the the third channel has to be faster than the other two. This guarantees "clear" audio signal activation. But doing this the third channel will turn off in advance which will result in a false tone switching. The
correct tone has to be switched on according to the state of comparator DA10.2 in that moment and retain this state until the end of sound indication.
Component DA10.3, switch and group of R83 and C35 form a circuit realizing this principle. When volume increases (the coil is close to the metal) at the output of the comparator DA10.3 is established a high-level signal that opens the switch, and the signal from DA10.2 passes through R83, C35 to the input of multiplexer. When volume decreases (the coil is removed from the metal) at the output DA10.3 appears zero voltage, the switch is turned off, and the state of the comparator is retained by the capacitor C35.

Modulator and audio amplifier
Audio signal that appears on the amplifier, formed by multiplying the volume control signal, is taken from VT and output of multiplexer DA11. Multiplyer is implemented by transistor VT6. Output stage transistors VT4 and VT5 work in switch mode and drives the speaker.

Power supply
Most of the components of the device operate on dual supply voltage +/-5V. Regulator SR4 provides +5V. VT7, VT8 and VT9 form a converter, alowing together with doubler and regulator SR5 to provide -5V, as well as +/-13V for the supply of synchronous detector amplifiers. This allows to extend the operating range of opamps and to work with unbalanced coil, which happens at big variations in temperature and increase the stability of device.

[lucifer]

Thank you Lucifer.
Is it Anker 50????
I yes, i constructed the Anker SS60 before 2..3 years.
Regards

Yes, it is Anker50.
Since you have constructed it, what is your experience with it? Is it so sensitive as stated in text?

I'm almost ready with translation from Russian.

[Geo]

I missed one opamp:
УД708 - uA741

I think even better parts can be used.

Geo, what you mean? Cannot see the schematic?
Check this link:
http://md04.narod.ru/An50/An50.htm

Thank you Lucifer.
Is it Anker 50????
I yes, i constructed the Anker SS60 before 2..3 years.
Regards

[mesy64]

this detector have discrimition??????maximom detect depth???
coils are very hard.please guide ??
please detect pin ic??
tank you

[lucifer]

wait for you my freind.
one question:
this detector have gruond balans and auto tune????

Yes, it has ground balance.

[mesy64]

I will translate the full description of schematic and will post it here soon.
For building the coil it is enough to follow the number of turns and wire diameter. Description says that it is a spider coil type. See image.

wait for you my freind.
one question:
this detector have gruond balans and auto tune????

[lucifer]

tank you dear lucifer
lucifer you can help me for build coil for this detector .l3 an l2?
your bilive abuot depth this detector for avrage taget????
can i build this detector t/r locator .t/r replace bi????

I will translate the full description of schematic and will post it here soon.
For building the coil it is enough to follow the number of turns and wire diameter. Description says that it is a spider coil type. See image.

[mesy64]

Here are some analog parts I just found
ICs:
1401UD3 - LM346
1401CA1 - LM339
561KT3 - CD4066B

Transistors:
КТ817Б - BD233
КТ816Г - BD238
КТ3107 - ВС557С
КТ815 - BD135
КТ3102 - BC546,BC547

tank you dear lucifer
lucifer you can help me for build coil for this detector .l3 an l2?
your bilive abuot depth this detector for avrage taget????
can i build this detector t/r locator .t/r replace bi????

[lucifer]

I missed one opamp:
УД708 - uA741

I think even better parts can be used.

Geo, what you mean? Cannot see the schematic?
Check this link:
http://md04.narod.ru/An50/An50.htm

[Geo]

Why i can't see the icon of schematic?????

[lucifer]

Here are some analog parts I just found
ICs:
1401UD3 - LM346
1401CA1 - LM339
561KT3 - CD4066B

Transistors:
КТ817Б - BD233
КТ816Г - BD238
КТ3107 - ВС557С
КТ815 - BD135
КТ3102 - BC546,BC547

[lucifer]

Yeah, if what the text states is true, it should be a quite sensitive detector.
I will try to post analog part list tomorrow.

[mesy64]

Hi,
It's an interesting schematic. Not too much to translate. Here's the description:

pin 8 and pin 9 of IC 1401 УД3 are connected through 200k resistor to ground.

L1 (transmit coil) - 75 turns of 0.4 enameled copper wire

L2 (receive coil) - about 250 turns of 0.15 copper wire

L3 (compensating coil) - 25 turns of 0.15 copper wire

L1 and L3 are wound under a common shield

When tuning the sensor it is possible to change places of L2 and L3

When 25 cm sensor is used sensitivity at air is 45-50 cm for a small coin (about 2 mm)

tank you dear lucifer
this detector is very good50 cm for coin......
please translate part list to english .or like english part(ic & transistors)