Originally posted by waltr
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The thing is that if I set the delay to minimum, the thin gold ring doesn't even sound. Perhaps the pot is not welded in the correct position, even though I'm really sure it is (I don't have the PCB right now). Tomorrow I will check this and do a test with a Silver coin and post the results. About the damping resistor: how can I adjust it? Do I have to connect a 1k potentiometer in series with the damping resistor and check with the oscilloscope with diferent values of it (I don't know if there's a threat dedicated to this inquiry, but I couldn't find it)? Also, I would like to know what value and where I have to check, since I've never used an oscilloscope, but I'm willing to learn . -
Thin, small and jewelry gold are low conductors with short TC (time constants) so you need to set delay to minimum not maximum to detect these targets.
Have you tried a Sliver coin which has a longer TC?
What about the Damping resistor value??
You really do need an O'scope to adjust the damping resistor value to obtain 'critical' damping.Leave a comment:
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Hi again
Luckily I didn't stuck in any other step. I have finally built my detector, the problem is that the detection depth is very poor. It detects a gold ring at 10cm maximum and a 2€ coin the same depth. I have no oscilloscope so I adjusted R6 so that it gives 0V in U2 pin 6 just like the manual says, and I adjusted R14 in step 7 instead of 6 because I have no oscilloscope and set the voltage level in U7 pin 1 at 2.3V previously shorting pin1 to p2 of PL2. The thing is that for those values, initially, for a 0.37mH (370 uH) 9" diameter coil, the detection is less than 5 cm for a gold ring and a little bit thin gold ring isn't even detected (perhaps it's too thin), and with a 0,45 mH (450 uH) 15 cm diameter coil, the thin gold ring is detected but really low depth and a gold ring at 10 cm as I said before. The delay is at maximum value. I don't know what to do for changing this so I am asking for help. I'm more interested in setting up the detector for gold rings rather than coins if it's possible. Thanks for the help.
edit: forgot to mention I am using the damping resistor that comes with the silverdog.co.uk kit.Leave a comment:
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Thanks for your help, it works now. I'm in step 5 now, and experiencing some problems which I'm trying to fix. If I have to ask for help, shall I make a new thread or continue in this one?Leave a comment:
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Q1 should be an IRF9640. The 9530 only has a VDS of -100V.
The first thing I would suggest is that you tidy up the solder joints, and also cut the long wires on the rear of the PCB. It's difficult to see from the photo, but it looks like some of these long wires may be creating a short-circuit.Leave a comment:
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Stuck in step 3
Hi. First of all, I am an inexperienced person in electronics, so yes, I know my solders are really bad. Yes, I know maybe I wasn't careful enough, and maybe I messed it up.The thing is that originally I reached step 4 but a sound in the headphones wouldn't appear when getting them near the coil (420 uH), and at this point I did again the speaker test in U4 pin 4 and 0V and it didn't work. That was when I took out the U4 IC, placed it again and it worked (the speaker test, not step 4 test). That's when the speaker test from step 3 worked, but the headphones test form step 4 still wouldn't work. That's when I tried to change the 9530N mosfet that I had put in the PCB with the one that came with the kit. I put another one because in the kit came the 9640, so I thought it was mistaken with the 9530. I just did this to see if my guess was right or not, but it didn't work either. But the next day, I accidentaly connected the R1 between the up pin of CONN1 and the up pin from R3 and it worked, and the buzzer that you can see in the picture sounded really loud (with the 9640 mosfet), but the mosfet was super hot, so I stopped it and replaced it by the 9530. The thing is that now neither connecting the R1 and coil in place nor doing that connection with R3 it works. I checked some PCB traces related to the mosfet and the coil and they work fine, even though they look like burnt in the picture (yes, I know the mosfet is terribly solded, but I'm not skilled in desoldering). Now the mosfet (9530) has a -+17.52 V in its left and right legsfrom U7 pin 4, and the -5 and +5 V power supply works, and the speaker test from step 3 works too. In conclusion, step 1, 2 and 3 are checked, but step 4 doesn't work. I hope you can help me and with the information I've given. If anything else is needed I will tell you. Pictures: there doesn't appear the damping resistor, but I used it in the tests.
PCB: (front)
(back)
PCB and coil:
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