ProScan project

[ares_world]

Not just big an enormous THANK YOU to all. You've been very helpful.

Now I found 14 pin UA709 and I plan to use it. I will modify the psb so it fits and use only the pins that I need. I am sure I will find it on eBay but the shipment will cost more then everything else and I'll have to wait a long time for the delivery.

I thank you for taking time out to answer my questions. I really appreciate and value your support. Thank you again.

[maikl]

Why not try the LM318? Cheaper than LM709, and can be easily found.

[porkluvr]

Not just big an enormous THANK YOU to all. You've been very helpful.

Now I found 14 pin UA709 and I plan to use it. I will modify the psb so it fits and use only the pins that I need. I am sure I will find it on eBay but the shipment will cost more then everything else and I'll have to wait a long time for the delivery.

I thank you for taking time out to answer my questions. I really appreciate and value your support. Thank you again.

What constitutes a long time?

Where are you located? I feel sort of guilty about not vociferifously warning you about the high likelyhood that you won't find the opamp you need, and I really hate to hear you say you will modify the board to fit a 14-pin version. Isn't there another way?

If your location is not too third worldly (such as where mail takes more than 6 months to deliver) I could probably ship you one or two of my extra Ua709. New, old stock. I'll probably never use them (I have extras). Any other hard to find parts you've been needing ? (Don't go wild).
Its a -tenuous- offer (I reserve the option to back out if you give me an impossible location).

[kt315]

I have a nice board for proscan. PM me if you are interesting.

[kt315]

Paulo Viegas, Portugal

ProScan Pulse Induction Metal Detector
Schematic (PDF-131K)
PC Board (JPEG-167K)
Parts Placement (JPEG-134K)
Here it is!

This is the PI metal detector first introduced in ProScan site (www.polbox.com/p/proscan/schemat.htm). The schematic was redrawn and revised by me (Paulo Viegas) and Piotr from Proscan.

The components

Capacitors:

Non-polarized: Use good quality polyester capacitors, except for pF capacitors which can be ceramic.

Polarized: Electrolytic, voltage as indicated on plan.

Resistors

Use 1/4 watt, 1% or 5% tolerance

IC's

DO NOT USE IC SUPPORTS (sockets), those can create inductance and capacitance, and we do not want that! For 709 I recommend using the TO99 version.

VR's

Use the mini version, horizontal placement.

USE ONLY NEW COMPONENTS

Component List
Part Value
Capacitors
C1 100uF/16
C2,C13 47nF/63
C3,C11 100nF
C4 1nF/63
C5,C24,C15,C16,C17,C19 47uF/16
C6 47nF
C7,C10,C12 150nF
C8 10pF
C9 3.3pF
C14 15nF
C18 68uF/25
C21,C22,C23 1nF
Diodes
D1,D2,D3,D4,D6,D7 1N4148
Variable Resistor (mini VR)
P1,P2 100K
P3 10K
Resistors (1/4W, 1% or 5% Tol.)
R1 43K
R2,R7,R13 1.1K
R3,R10 1K
R4 330
R5,R12 220
R6 100
R8 300
R9 820
R11 520K
R14,R16 10K
R15 110
R17,R21 2.3K
R18 750K
R19 220
R20 6.8K
R22 1M
R23,R26 11K
R24 130K
R25 30K
R32,R35 18K
R33,R36 8.2K
R34 91K
R709 100K
Transistors
T1 BC560C
T2 BD911
T3 BF245
T4 BC560C
IC's
U1,U5,U6 555
U2 79L05
U3 709 (MAA501 as in plan, is a Czech equivalent to 709)
U4 741
U7 78L10C
U8 4093
Other
L1 Search Coil, 20cm diameter of 25 windings of insulated copper wire (~22AWG)
S1 Female Jack Phones for PCB (optional)
PCB

The PCB for this project is a JPG file (PCB1), the final printed dimensions should be ~65mm X ~130mm. I recommend using the photo process to create the tracks, since the circuit is more or less complicated. After printing PCB1 flip the paper, the printed surface is the one that will be in contact with the copper layer. The components placement is in file PCB2.

Please note that there's four jumps, make then with standard isolated copper wire. The S1 (jack support) is optional, and can be placed in the case. Keep the components with short leads, and close to the pcb, to avoid capacitance and inductance.

Note: I've taken much care in making this pcb, I believe no tracks were forgotten (since this is insured by the software), nevertheless if any error as to be found, please inform me right away. [[email protected]]

IMPORTANT

After making the pcb, please check the tracks that go inside 4093 pins, insure that they are not short-circuited (correct with a x-acto blade if needed).

Circuit Description

"Basically U1 is a timer integrated circuit that is wired as a pulse generator. The output on pin 3 is a negative going pulse of a width that determines the width of the transmitter pulse. This is repeated at a certain frequency that is the transmitter pulse rate. This pulse train drives T1, which inverts it so that it is then a positive pulse driving the base of T2. T2 is the transmitter output stage driving the search coil, L1, in its collector. U2 is a voltage regulator that takes the negative battery voltage and gives -5V output for the receiver amplifiers U3 and U4. R7 across the coil is a damping resistor to stop the coil ringing. The live side of the coil then goes through a 300? ohm resistor to pin 2 of U3 which is a wide band receiver amplifier. The two back to back diodes prevent the transmitter switching transients from damaging U3. After amplification the signal goes to the sampling gate T3. This acts as a switch that is closed until a short time after the transmitter pulse has ended (pulse delay) This delay is generated by the 4093 dual monostable which is triggered via C4 from the transmitter waveform. The first half on the 4093 generates the delay duration while the second half generates the time that the gate stays open. U4 is a single ended integrator which takes a running average of the samples of the amplified receiver waveform. When there is no metal near the coil the sample will be approximately zero; bring metal near to the coil and the sampled decaying waveform from the metal will cause the output of U4 to rise. This dc output goes via R17 to the transistor T4 which controls another timer IC, U5, to generate the audio pulses. The audio output is a tick that increases in frequency as metal is brought closer to the coil. The threshold tick is set by P3 that alters the bias on the other input of U4. Headphones can be connected to pins 3 and 2 of the connector on the right of the schematic. A resistor in series here might be necessary to adjust the volume. At the top left of the schematic U6, is another timer that generates a separate pulse train that is then rectified by the diodes D1-D4 to give a positive dc voltage which is then supplied to the positive 10V regulator U7 which gives the positive supply necessary for the receiver IC's. P1 is a preset resistor that sets the dc output level on pin 6 of U3 to 0 volts. It is useful to connect an oscilloscope to this point for testing to see that everything is working OK. The only thing that I can't show here are the various waveforms and their relationship with each other. These are controlled by the components around the timers and the monostables and are fixed by the values given in the schematic. So if everything is assembled right the only setup adjustment is P1." Eric Foster

Eric's suggestion:

"I would suggest making R8 1K0, R11 1M0 and deleting R9. This will give a gain of 1000 for the first stage and the 709 will be stable with the compensation values given. What sometimes fails rather than the diode is the input resistor R8 and possibly the damping resistor. Both of these resistors experience the peak voltage across them and can go open circuit unless a high quality metal film resistor of adequate rating is used."

Acknowledgements

I would like to thank:
Piotr for giving the first schematic and revising the new one.
Eric Foster for giving the explanation on the circuit, and commenting it
All the guys (Phil, Vlad, ...) that commented this on Eric Foster's Forum (http://www.insidetheweb.com/messageb...s.cgi/mb122618)

My wife, for being sooooo patient when "I'm on the computer".

Regards to all,
Paulo Viegas, Portugal
[email protected]
P.S. - Sorry for any English error!!

Notice

Here is a note from Paulo regarding possible errors in the Proscan:

I've received mail regarding errors in Proscan PCB an possible error in schematic. I've corrected the error for T2 BD911 in the PCB (my pcb program had this component in incorrect pin-out).

Now, regarding T4 BC560 i had a post saying that it was incorrect wired in scheamatic, i'm waiting for confirmation on this, if so i'll correct it also. -Paulo

I will post the corrections as soon as I hear back from Paulo. -Carl (06/21/99)

[porkluvr]

I found this pi project in the project section but I can't find any comments. Has anyone tested this detector. The reason why I ask is because I want to make my first metal detector and this one seems to be simple and straightforward. However, I want the detector to work and be practical. I don't expect wonders from it. I would be very grateful if anyone can give there opinion and a possibly a different project if this one is no good. Sorry for my English

Sorry if this question seems a bit untimely, er, late: Are/ were you planning on etching your own PCB? (Of course, the answer is yes, correct??)

It should be a relatively easy matter to adjust the pads,traces on your preamp IC so that they would accomodate a newer, more readily available opamp. Beware, there is not a "one size fits all" deal, because there are several different offset adjustment pinout schemes you would encounter with different opamps.

[Jerry]

[QUOTE=kt315;155461
IMPORTANT

After making the pcb, please check the tracks that go inside 4093 pins, insure that they are not short-circuited (correct with a x-acto blade if needed).

[/QUOTE]

That is so true! Every pcb I have made has required proving out all all of the circuit traces with an ohm meter. The smallest piece of lint on the artwork can produce a hairline break in the traces.

Jerry

[kt315]

DVD with archive will be FREE FOR YOU if you are interested in PCB.

[oros27]

I got this circuit built a buddy and I found the problem (for those who have made this project) now it works