?Strip Board? layout for the ?Bandido II U Max?.

		Quote:			Posted by Mike In2mud
	Thanks David for that link that was exactly the info I was looking for. I now know that the circuit is not at fault, but that it was the way I wound the coil. I tried to get the null point as near to zero as possible, when in fact I should have left it at 300mV. With that coil I don't think the ..Discriminate.. will ever work properly. In answer to your question about the electolytics C38 & C39 the capacitor pin marked with a minus (-) sign goes to the 0v ..Green track.. All the best Mike.

Hello Everyone . If I remember correctly a proper working Tesoro Bandido coil nulled at 5 to 30 millivolts maximum . I will try to post the all correct final data of the search coil . There are no caps or resistors in the coil itself . But the tx capacitor on the circuit board might need to changed from the original value on the schematic to run at 10 khz...........Regards.............Eugene

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		Quote:			Posted by Mike In2mud
	Hi Edouard and David. I have not heard from you recently  how are you getting on with your ..Stripboard.. projects. I have finished building mine, but have had a series of disasters making the detector coil. I am now winding another set of coils and have had to buy another coil cover to put it in. The coil works fine and will detect an ..Old English Penny.. at a test depth of 10 inches (250 mm) its just that the fibre glass resin I used has not set properly and will absorb water if I use it. I also have another problem which I cannot seem to resolve, whereby the ..Discriminate Pot.. does not work properly and only discriminates on the first 10% of its range. I will post some more photos soon. All the best Mike.

Hi Eugene, Thanks for the info,
Please see above from a previous post,  it details the problems I have been having with my coils.

You mentioned in your post that the Bandido coil nulled at 5 to 30 mV, well after potting the 1st coil in resin, the TX ended up at ..9.994kHz.. and after the first amp stage  the signal was a 40mV sine wave.

My Discriminate problems.
I have double checked the ..Discriminate.. circuit, the layout  and components around it, but I am not sure quite how that part of the circuit works, so am not sure what waveforms to expect, it only produces a signal on 10% of the pot  range and is then cancelled out with a square wave as the pot is moved C/Wise.

I think I will build the ..Double  D coil.. as you suggest as I cannot repeat the results of the first coil when building the second coil. One question though :- Do you tune BOTH coils to 10kHz with the TX circuit, before moving to the next stage.

Best regards Mike.


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Hello Mike . I am looking for a completed drawing of the Bandido that has all the test point voltages shown across the pcb board . I saw one years ago and can not find it yet . Look at the example from another forum I have shown here below on oscilloscope test points and most are at the outputs of each IC , if you were building the Golden Sabre model you would have been done by now and outside finding goodies !! Also , a Tesoro search coil will work on different Tesoro machines 10, 12, or 14 khz , the Tx coil is usually constant around 5.75 mh inductance and 22 ohms dc resistance . As you know the different capacitance value of each models oscillator circuit results in a different transmit frequency . It seems the coils are not set by a resonant frequency at the factory but are dependant on a TX-RX  phase difference in the coil itself which help you obtain your Bandidos 120 degrees of ED [discrimination] . You also might want to check your disc. potentiometer if you still have problems . Also remember that there is are 2 RX coils in many Tesoro concentric search coils and the number of wire turns on RX2 sets your null . Make your 22 centimeter DD coil and I think you will complete your Bandido very soon !! I will post more later as I find important specs.
Regards........Eugene

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		Quote:			Posted by Mike In2mud
	Hi Eugene, When I made my coil I monitored the RX I/P and got that to read Zero, then moved the probe to pin 7 of IC7b and tried to get that to as near zero as possible. I didn't know at the time that I needed to leave that at 300mV. So I think unfortunately the coil will never discriminate properly. Eugene, can you tell me when making the ..DD coils.. do I need to tune BOTH coils to 10kHz using the TX circuit, before moving to the next stage. Best regards Mike.

Hello Mike . Wind two coils 22cm diameter each and use 0.3 mm wire , wind about 120 turns tightly for each coil . Then neatly wrap in aluminum tape or foil . I will post you a picture . Place the coil on a temporary piece of thin wood or a plastic flat plate . Do not glue or epoxy anything yet . Bend each wrapped coil to a "D" shape . Place the RX connecting coil on the bottom and the TX connected coil on top. Hook up your voltmeter to the RX leads and adjust top coil till signal/voltage decreases to zero . Then temporarily secure with masking tape . Test TX coil for frequency with an oscilloscope . When you first start winding/making search coils make sure you have plenty of wire , like plenty extra !!.....Well , thats enough to get you started .......Regards......Eugene

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		Quote:			Posted by Mike In2mud
	Thanks Eugene for the reply and the attachment, sorry I read and answered your post on page 7 and didn't see the other post on page 8 until afterwards it was very helpful. Many thanks Mike. Posted on: July 08, 2009, 08:33:31 PM Hello Eugene, I have wound one the coils as per your instruction, except that the largest wire size I have is ..33swg (English size).. which is ..0.2mm.. therefore when I wound :- 120 turns I got 31.10 ohms, 8.487kHz 110 turns I got 28.00 ohms, 9.184kHz 100 turns I got 25.05 ohms, 10.009kHz   90 turns I got 22.06 ohms, 11.200kHz All monitored at the TX. Am I right in thinking that the important value is ..22 ohms.. and that therefore I should use the ..90 turn.. example. I have been experimenting, I tried using two TX coils I?d originally tuned to 10kHz  (25.15 ohms) for the Bandido. I formed them into two ?D? shapes laid them out and nulled them, they were more sensitive (as you said they would be) than the concentric coil I have been using, I varied the nulled o/p to read different values at ..pin 7 of IC7b.. but the ?Discriminate? didn?t work any different than before. I realise that the coils weren?t 22 ohms, but this was just an experiment. I?m not sure if I?ll be able to test them at 22 ohms as the glue has probably hardened too much to unwind them. Regards Mike.

Excellent Work Mike !!!  You are correct use the 90 turns for both the TX and RX and then change the Rx capacitor to 22 pf and then change the TX capacitance of C2 to obtain 10 Khz transmit frequency and see what happens . And yes I forgot the formula for calculating parallel tank oscillator frequency [L and C] . I do have occassional altzheimers once and a while . Are you using the schematic below ?....... Great work you are doing on this project and for the Thunting.com Forum !!!

Regards..........Eugene

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