possible big problem on surf 1.2

[bainsey]

Well I have finally got it all wired up but when I turn it on all I get is a buzzing from around the offset trimmer, no.sound from little speaker, when I try to.adjust the offset by ne55 chip pin 6 and ground it does not adjust.do.you.think my.trimmer is broken? if so is there any test I can do.with a multi meter to.find out?

[bainsey]

Right scrap that, had multimeter on wrong chip doh! Failing eyesight. It's working now but not picking up any metal. Maybe the coil. If I coil is made bad will this stop it detecting all together or should it still work slightly? I can't think of anything else but the coil as the problem

[WM6]

Why you need to start new topic for every problem you face with your Surf PI?

[bainsey]

Why you need to start new topic for every problem you face with your Surf PI?

The sorry about that, wont happen again. Problem still stands, the circuit is working sound is coming out of speaker and trimmer had been set. But all the're is is a constant hum. It does not detect any metal just a constant threshold sound. My coil was only a quick practice one. 8 inch bundled 0.56 enammaled copper wire with 20 turns, I know this is not correct but it was a quick one to test with.could the coil be the reason it's failing?

[bainsey]

surf pi help needed asap please!

Just checked the voltage across the coil connect on the board and it is only 0.32 v. this can't be right can it? I think this is possibly the rEason I cant get it to run. What would be causing this do you think

Thanks
Andy

[WM6]

Surf PI is very tolerate regarding coil, you need to check other things before coil. As first TX generating signal stage.
Do you have multimeter that can measure frequency (Hz) too?
Can you post here schematic of Surf PI you use, there are different arround?

[bainsey]

Hi, thanks for responding, this is going to sound real bad, I didn't use a schematic as I can't read them I referenced the numbers on the silk screen to.the part list to work out which went were and used the walk tthrough written on the Adrianandgenesse site to work out which way everything went. I have a multimeter but not sure if it has them measurements. I will have a look,

[bainsey]

No I don't have the function on my multimeter to measure that, I have only.got voltage, current and resistance. I know it's not the coil but at the terminals for the coil the voltage is 0.3 ! I really just don't know what's up with it, all the welds went great and I'm 99% sure all the component are the right way round.

[WM6]

No I don't have the function on my multimeter to measure that, I have only.got voltage, current and resistance..

OK, no problem, you ca build your own simple audio testing utility out of an old small speaker or earpiece (nominal R from 8 to 32 Ohms) some insulated cable wire, testing clamp to connect to ground of your Surf PI, one resistor of 1kOhm and testing probe (you can made out of some hard insulate wire). Look at drawing:

.

After building your audio testing utility, test your TLC555 first (test probe at pin 3 of TLC555, clamp at one of Ground points). If TLC555 works properly you need to hear loud tone from your audio utility.

[Mohamed Ghitas]

hi all
i was having a problem exactly like bainsey problem but i made another PCB and it worked fine
the new one works very well with coil for testing 5.5cm ,0.4,29 turn but detects coin only at about 2cm range

i made a new coil with 20 cm ,0.4 ,14 turn and it works but only detect medium object at about 8 cm and coin at about 5cm

so iam in need to upgrade my metal detector
i used this one



and i made some recommended updates
i replaced the delay pot 10k with 50k
and connect 330 ohm at the emitter of 2n3906 and 3.3k from its base to +12v

so any idea

Notes :
i made the Hz tester and tested pin 3 at N555 and it gives beeeb so is it ok ??

[WM6]

Not only single "beeeb", you need to hear constant strong buzzing at pin 3 of 555, then it should be ok. And you can check the coil without any utility. It is enough to lean coil close to your ear, if you hear weak drone of sound/vibration, then your power MOSFET should work ok.

[Mohamed Ghitas]

ok iam hearing continues strong beeb from pin 3 at 555 and when i lean the coil close to my ears iam hearing very weak sound like small beebing

but iam still stuck with very low range

what else could be tested ??

another question
iam using the coil with one end and the other end is connected to the rest of the unused wire iam just scratching it and attaching it with crocodil is it ok or i must cut off the wire of its both to ends ??

[WM6]

What mean for you "very low range"?

[Mohamed Ghitas]

i mean it could detect medium object at about 8cm only and coin at 5cm or less

dose this could be problem ?

iam using the coil with one end and the other end is connected to the rest of the unused wire iam just scratching it and attaching it with crocodile is it ok or i must cut off the coil wire fromits both to ends ??

[WM6]

Not so bad sensitivity for start.

Bad sensitivity can be related to bad coil construction (post photo of your coil here) or unproper done of tuning procedure (repeat tuning procedure).
Another possibilities is that your working space is not clean of metal in vicinity of coil (1m arond of coil position) and different EMI sources (TV, CRTs, Neon lamps, transformators etc. - check this).