Surf PI Pro

[au1]

Looks like you were posting at the same time and beat me. Glad you at least got a siren. Thats an improvement.
I assume you've adjusted R10? If so, what kind of coax are you using? I found that twisted pair doesn't work for me and I get almost no sensitivity.
Do you have an inductance meter?

[au1]

2N3906

Hey Sdesic,
Sorry to hear about your detector not working. Thats's a bummer! I can tell from your board you put forth a fair amount of effort. If the only difference between mine and yours is the MPSA13 then I'd lean towards that being the issue. You can't source them? Can you receive packages from china? If so, you can find most parts reasonable and free shipping. It might take 2 months or more to get them though.
Here's a couple things I found out about this layout. Due to the size, I replaced the electrolytic feeding the sound with a 220uf even though the 470uf worked ok. I also
used a 1/2 watt resistor for the 12 ohm. Everything works good.
About replacing R2 with a trimmer. I doubt thats going to help your problem. But it will definately help the sensitivity. It apparently applies more current to the coil, the lower the resistance. I'm running mine at about 2K. Got about 3 to 4 inches more reach. But at the cost of shorter battery life. I don't mind. Batteries aren't too expensive.
And by reducing R2 I also noted that I get some unusual noise that wasn't there before. I just turn the threshold up a bit. All is well.
I'd offer to send you a MPSA13 and a ICL7660 but I fear what the postage might be to Bosnia.

PS. I used 150 ohms for R34. But I doubt thats your problem.

Good Luck!

[sdesic]

Replaced BC879 and there is constant sound on speaker.
Can be silenced with volume pot, that is good.

Siren MD

It can be changed by R2 trimmer 5k
Doesn't change a thing if I wave metal objects in front of coil or adjust any of pots delay, sens or treshold.

[ApBerg]

ApBerg,
I think BC557 is OK ?
EBC it is on both
http://www.robosapiensindia.com/reso...557%5B1%5D.pdf

Hmmm... look at it....and check it ..

[sdesic]

Siemens and NXP (Philips) both make BC879 and according to product datasheets their pinouts are exactly reversed from each other. So that, facing the flat part of the transistor:
NXP BC879 pinout is ECB and
Siemens BC879 pinout is BCE.

So, how you connect it might depend on who made it. Most digital multimeters have a diode check function that makes checking BJT pinouts very easy. It's maybe a little more difficult with darlingtons, but it should still be possible.

I think you are wrong about that pinout
Siemens and Philips have same pinouts ... TO-92 housing

http://www.datasheetcatalog.net/de/datasheets_pdf/B/C/8/7/BC879.shtml

[sdesic]

ApBerg,
I think BC557 is OK ?
EBC it is on both
http://www.robosapiensindia.com/reso...557%5B1%5D.pdf

[sdesic]

My PC speaker is more sensitive to changes than this audio part.
I am hearing buzzing tone while I adjust R2 5k trimmer and it changes with it.
If I move coil close to speaker it changes sound.
No sound from audio part of PI Pro.

[sdesic]

porkluvr I have darlington marked C879 W89

[ApBerg]

I have seen one more replacement ... received BC557C in place of 2N3906
same pinout for both

I am going to try trimmer in place of R2 3.3k

Think you have to check for the EBC connections ...

[porkluvr]

Siemens and NXP (Philips) both make BC879 and according to product datasheets their pinouts are exactly reversed from each other. So that, facing the flat part of the transistor:
NXP BC879 pinout is ECB and
Siemens BC879 pinout is BCE.

So, how you connect it might depend on who made it. Most digital multimeters have a diode check function that makes checking BJT pinouts very easy. It's maybe a little more difficult with darlingtons, but it should still be possible.

[sdesic]

I have seen one more replacement ... received BC557C in place of 2N3906
same pinout for both

I am going to try trimmer in place of R2 3.3k

[sdesic]

If you don't have an oscilloscope it will be difficult to find the error. I would suspect the audio stage, total current looks good. Why don't you desolder the BC879 and test it in a separate circuit?

Don't have access to oscilloscope yet, I have another BC879 but don't know if it would help.
Is it OK to replace with same pins position ?

http://www.geotech1.com/forums/attachment.php?attachmentid=23365

I will try to resolder few parts or leads in audio part... tryed connecting audio from mp3 player to base of BC879 and it passes to speaker but it is not amplified or clear, very faint sound.

[joop]

If you don't have an oscilloscope it will be difficult to find the error. I would suspect the audio stage, total current looks good. Why don't you desolder the BC879 and test it in a separate circuit?

[sdesic]

Coil is 21 cm - 22 turns copper enameled wire 0.4 mm
1.6 ohms

My amp meter was set on 10 A so it was rounded to 60 - 70 mA ... used another one and it is 50.6 mA
Tryed delay and other pots in diferent positions but same result... no sound.

[ApBerg]

I have not looked at the specs from the BC879...but look here http://www.geotech1.com/forums/showt...PRO-VDI/page26