it doesnt work.

[Dan]

Hi, I just tried the proscan PI MD. I made it on a board and it appears that it wont work. I think I might have to try to actually make the board exactly as shown, not just useing jumpers on the back. I fear there is to much chance for error as well as a lot of unwanted inductance and interferance. I also have shelved it but after reading this forum I think I might just take it out again and see if i can make it work.I had a lot of trouble finding BC560C but found substitute.

[ian]

Re: it doesnt work.

hi dan
i have built mine on a etched board and mine dont work either ive checked it and every thing seems ok but doesnt work the coil output transistor gets really hot some one suggested that is was the timeing of u1 leaving it on to long and off to short after looking at r1 and r2 i think it might be but not sure if my calculations are right let me know what you think
regards ian

[Randy Seden]

Re: it doesnt work.

Ditto guys and I carefully selected the highest quality capacitors and resistors you can buy. Didn't have trouble with the substitution once I viewed the specs., but what I saw was the driving ckt. is faulty. The 555 performed no problem though. When I get over being ticked at the 2nd PI ckt. with design problems ,I'll redo the bias on the mosfet as it looks like it wants to work. Mosfets are so darn easy to bias compared to BJT's,but they are considerably more fragile. Otherwise I'll just buy the PI kit from Magenta and be done with it.

Randy Seden-WD6ELU
Simi Valley,CA

[ian]

Re: does any one know if it does work

hi anybody out there built a proscan that actually works if so leave some tips on how to get it going

[Piotr]

Which Proscan PI?




Hi Ian,

Proscan PI is a modified version of Sandbanks PI that appeared in 70's in Practical Electronics. On my page I put a schematic which was blury. Paulo from Portugal redraw it. Unfortunately he mistook what I have overlooked.
Go to the link below where you will find the "oryginal" Proscan PI (as all of you name it). Will try to attach it also.

It surely works. But do not expect miracles, as far as stability is concerned. Depth is decent. If you still have problems email me.

Piotr



proscan

[ian]

Re: Which Proscan PI?

hi piotr
the only difference i see is c1 which on shematic is 1000uf/16 yet in component list is
100uf/16 is this what you mean when you say over looked

ian

[ian]

Re: Which Proscan PI?

hi piotr found problem the pin out on bd911
is to220 on mine B C E on pcb C B E so i changed it round and have got the coil pulsing
but still not working i took voltage readings of all the pins on 709 amp and they were all input voltage do you think this has blown or gone short circuit same reading on every pin
doesnt sound right ? also p1 has no effect on pin 6

ian

[Dan]

Re: Which Proscan PI?

HI Ian,
I also switched to220 around and found that the coil was pulsing good. But nothing changed when i adjusted the pots. All it did was make a steady tone that didnt change at all when the coil was brought near metal. The tone did change when I touched certain spots on the back of the board, but thats caused by me. Something strange also happened, when the detector was on i had used a metal coffee can as my test piece of metal -- well the pulsing coil had slipped off and fell around the can. I heard something but not through the ear piece, rather the sound which was a buzz was coming from the coffee can itself. My guess is that the pulsing coil turned the coffee can into a very primitive sort of speaker with the hollow part amplifying the sound somewhat. Well thats all the action I got out of it. Let me know if you come up with anything. (maybe I blew up my 709 as well?)
Thanks,
Dan from Canada.

[Piotr]

corrections to the diagram

Hi Ian and Dan,

I had some Proscan PIs in my hand and must say it is not easy to blow the 709. I think you all have voltage supply problems. Please note that on the Paulo's diagram the GND pin of U7 is wrongly connected to the GND. It should be connected to the 10,5V. The same goes for C18 and D4. Also note that C1 should be 1000uF instead of 100uF.

After corrections, the voltage between +10,5 V and pin 7 of U3 should read 10V and between +10,5 V and pin 4 of U3 should be -5V. Check it.

Piotr

Dan. I like your speaker made of coffe can. How about patenting it;-)

[ian]

Re: Which Proscan PI?

hi dan what you have decribed here is identical to mine with the buzzing but i do get clicks which the pots speed up or slow down when i turn them but only when the coil is not connected otherwise like yours a buzz when its connected but nothing when you bring metal to it
what voltages do you get off the 709 mine is the input voltage on every pin, pin 6 doesnt change with p1 neither im wondering if ive fryed 709 if yours reads the same then maybe it was because bd911 was wired wrong in the first place let me know your results

ian

[ian]

Re: corrections to the diagram questions??? piotr

hi piotr
im using the to92 package for U7 IN:GROUND:OUT if viewed from above with flat side facing you
are you saying that ground should go to the 10.5v live rail also do you mean turning round the capacitor and diode so the polarity is reversed EG + - - +

ian

[Dan]

Re: Which Proscan PI?

hi Ian,
What kind of 709 do you have? The one that i used was a can style round with a little stub sticking out. For some reason (My Dad) that stub was wired in as pin 1. Closer investigation in the manual produced a big DUH!! and a smack on the forehead. its really pin 8. Perhaps this has caused me to fry the 709. Remember that i also built mine on a board that is not etched so there might be a problem in the wiring even though ive checked a hundred times. One question for you is did you find BC560C? I looked at the specs and put in a 2N3906 as it seemed close. no stores around here had BC560C or it was on backorder or something stupid. I got the original schematic and i will do some comparisons to what i have and will let you know whats going on. But first I have to clean my desk. Dan.

[ian]

Re: Which Proscan PI?

hi dan
i could only get bc560b but someone said it didnt matter i reckon by the fact you said your coil was pusling it wont matter if you check the output with a scope you will see that it just inverts output 3 of 555 to turn on the coil transistor at the right frequency and its obviously doing that so i wouldnt worry did you understand exectly what piotr meant about u7 c18 and d4 i took he meant turn them around the polarity and u7 was a different pin out but im not 100% sure let me know what you think

ian

[Dan]

Re: Which Proscan PI?

Hi Ian,
WOW! I got it to work! And it works good too!
Heres what you do with the info that you got: the change of C1 100u to 1000u is right. Then the center pin of U7 ( ground ) goes to the positive 10.5v, (i'm sure you got this) well then- last one- from D4 to the negative side of C18 THEN to positive 10.5v (use a jumper) Because your board is etched you will have to eliminate the connection between neg C18 to the main neg line that runs through the center of the board. I did this and had excellent results. It sprang to life. I still have to tweak it but it appears to be one the right track.
let me know what how you do. Dan.

[Dan]

Re: corrections to the diagram

Hi Piotr,
I did what you said and it works! Its amazing.
Thankyou verymuch for all your help. All i have to do is mount it as an actual real metal detector so i can find things. Too bad we just got 40cm of snow on tuesday. Thanks again, Dan.