Surf PI - successful build

[SVEN1]

Out hunting in the city areas EMI tends to rise by 10am, when the world comes alive. And settles back down after 6pm when folks get back home from work.
So if out hunting, might have to make avery very slight frequency adjust now and then. Not so much at the beach. Had one city beach up north, get within a certain area
and the EMi became nasty, couldn't run any VLF machine there using more than 50% (gain, sensitivity) resulting in loss of depth. My PI was bothered but, sould still hunt.
It was like a 50' wide area, like some one sent out a EMI beam . You knew when you were getting close and exiting this zone. Smaller coil helped in this area over the larger coil.
I have hunted places that never needed a frequency adjustment and the threshold purred very slowly without a hic-cup.

[chrisw]

Anyone know where the original crossbow enclosure was from and what size it was?

Chris

[Qiaozhi]

Anyone know where the original crossbow enclosure was from and what size it was?

Chris

It came from here ->
http://www.lincolnbinns.com/uniobox-2/

[chrisw]

Thanks for that George.

[Qiaozhi]

Thanks for that George.

As you can see, these enclosures are high quality anodised (and not cheap). All the holes were CNC punched, and the panels were laser printed. It will be a very very long time before any of the text wears off. There was also a carrier plate to support the battery pack and the internal speaker. The only problem is that they're not waterproof.

[chrisw]

Yes the boxes look really good quality, but as you say a little on the expensive side especially for the black. But as they say; you get what you pay for.

[chrisw]

Crossbow Low voltage LED

I have another Crossbow question. The low voltage LED. I connected a panel mounted 5mm LED in the board today. It is a low voltage 2V led. I set it to come on at 10.5 as the calibration guide says, but then stays on all the way up to the full voltage. If I then turn off the power and then turn it back on gradually, when I reach the 10.5V the led comes on all the way to 12V again.

This is working backwards or am I looking at this all wrong? I thought it should come on from low voltage to 10.5 then turn off all the way to full voltage.

I have a series resistor in line with the diode to limit the current to 10mA.

Any Ideas especially George

Chris

[Chet]

Hi Chris


I haven’t built the Crossbow yet but looking at the circuit I recommend the following checks;


1. Measure to make sure that the +5v and -5v are correct on pins 8 and 4.


2. Measure for approximately -2.5v on pin 3. This is ½ of the voltage between the -5v regulator and circuit ground. The -5v is divided equally by the two 100k resistors.


3. Measure for approximately -2.5v on pin 2 as you adjust the CERMET pot. The LED should go off and on as you adjust above and below -2.5v. The pot is dividing the voltage between -12v and ground (+12v) to set the trip point voltage near -2.5v.


I hope this is helpful,
Chet

[Qiaozhi]

Any Ideas especially George

Chris

I haven't looked at this design for about 4 years, but chrisw's advice is correct. You probably have the 1M trimmer adjusted to the wrong side of the threshold (junction of R45 and R46).

[chrisw]

Hi guys thanks for the replies. I have all the voltages at you show Chet. I can set the LED to come on at 10.5v but it is always on over 10.5V and always off under 10.5V which is working backwards. I cant see how I would have wired anything backwards because it is all on the pcb and I just have two holes for the led. I feel if pins 2 & 3 were reversed then it would work the right way round. Everything else on the board works beautifully and nice and deep on coins.

Chris

[SVEN1]

Chris I had the same problem with the LED and I even adjusted the power supply voltage to see if that would make a difference. At that point I also grabbed the coarse power supply adjust knob instead of the fine adjust, well accidentily peaked the supply voltage and popped a few parts. OOPs.

[chrisw]

Hi Sven, Sorry to hear about the missap, but thats interesting to hear you had the same problems.
Im wondering if the circuit is correct. Because I have used the correct parts, in the correct holes obviously. The rest of the board works perfectly so power supplies must all be ok. I even suspected the LED. I think I read George originally used a bigger LED which had a reverse breakdown voltage of 12v. My smaller LED has a reverse breakdown voltage of 5v so I thought maybe the voltage maybe goes a little high acros the LED and it conducts. I dont know if my theory is correct. But I stuck another LED in series to see if this made a difference but it doesnt. So it looks like I will have to leave the LED out because I am very pleased with the rest of the Crossbow.

[Qiaozhi]

OK guys, I've located the problem. The schematic is correct, and the LED should turn off when the inverting terminal of the LM311 falls below the -2.5V reference voltage. However, in my notes for the REV-A version I wrote: "Note: Nat Semi 1994 LM311 datasheet has pins 2 and 3 back-to-front! Use ST datasheet as reference."

Apparently I forgot to correct that error when REV-B was created. Also, bear in mind that I've never built a REV-B version myself. Unfortunately you will have to cut-and strap the tracks (swap over pins 2 and 3) to fix the battery warning circuit. The only problem is that one of the tracks runs under U8.

As this is a simple fix, I'll generate a new set of Gerber files later and send to Sven.

Edit: Actually, there is one other [simpler] fix ... reverse the LED, and connect the cathode to -5V.

[chrisw]

Thats great George thank you for sortin that for me. I had a funny feeling pins 2 and 3 were backwards, but my knowledge of electronics is limited so it was only a guess.
Thanks again
Chris

[kenny444]

Hi regarding the track cutting, I would do this, fit the IC in an extra turned pin socket, leave out pins 2 & 3 solder some resistor legs in the the socket and cross them over, solder to IC legs. No cutting, no track repairs, in the past I have done strange things like bend all the legs of an IC the wrong way and fit it to the back of a PCB, because of little working room, sounds odd but it works.