surf pi 1.2: building my first detector

[kasperfish]

Hi all,

I'm assembling a surf pi kit from silverdog. I have soldered all the components to the board and made a test coil. However its not working. I hope you experts can help me troubleshouting. I already did some measurements with my DMM but I don't have an oscilloscope. I did some soldering and electronics before but this is my biggest "electronics" project so far. I only have basic knowledge as my previous projects were arduino based and the major work was coding. I hope you guys can help me figuring out what is gone on.

power consumption with coil: 91 mA
power consumption no coil: 30 mA

U2 pin4: -4,7V
U2 pin6: 0,423V (this is the lowest I can get by turning the offset)
U2 pin7: 5V


U6 pin1: 1,3V
U6 pin2: 2,53V
U6 pin3: 0V
U6 pin4: -2,35V
U6 pin5: 5V
U6 pin6: 2,7V
U6 pin7: 1,3V
U6 pin5: -4,7

U1 pin1: 1,6mV
U1 pin2: 6,5V
U1 pin3: 12,2V
U1 pin4: 12,5V
U1 pin5: 12,6V
U1 pin6: 6,5V
U1 pin7: 6,5V
U1 pin8: 8,3V

Thank you in advance

[Tepco]

You provided very little information about detector behavior, what is exactly wrong wit it? Do you have any audio output, beep at turn on, and continuous tone at some point of threshold adjustment? Power consumption looks good (bit higher but not abnormal), +5V and -5V present, input amp not saturated, other voltages measured using just multimeter are not much relevant, describe problem in more details.

[kasperfish]

Hi Tepco,

thank you for your quick reply! I do not have any audio output at all. Not when I power up the device nor by adjusting the treshhold. I tested the piezo speaker and it is working fine. When I power up the board I hear a zooming sound coming from the coil. When I move a soda can over it I can hear changes in the zooming. My coil (200mm inner radius) is wound with 0.4mm copper wire with 15 turns. According to the calculator that is circulating on this forum it should give a coil with 0,326 mH inductance. I do not have special tools like an O-scope to do sophisticated measurements.
I'm not to sure that the orientation of U7 is correct because it is marked with a dot and a slit on opposite sides. Also maybe you can check the attached pictures (first post) and see if the other components (potentiometers, diodes) are orientated the right way. I'm a beginner like I said before so its possible that I did something really stupid. The picture attached to this post is from the back of the board to see the solder points. If you need more info/details, I'll be happy to provide them.


PS:
I soldered U6 accidentally straight on the board (so no holder, this was my first IC I soldered ever to a board. Maybe it is damaged by heat?)
I cleaned the back of the board with acetone and a nail brush (I didn't have alcohol)
I power the board with a small 12V lead acid battery (I don't use the integrated switch in the volume pot)

[kasperfish]

It seems that I made a mistake with the inductance calculator. I filled in the inner diameter instead of the inner radius. My coil only have 0.144mH inductance. I'll test this evening with a coil with more turns (0.4mm copper wire, 22turns -> 0,299mH). However I don't think this will be the cause of my problem. I should hear something out of the piezo buzzer with the bad coil, right?

[6666]

Seeing you have no sound, Have a look at this thread it may help you track down your problem.

http://www.geotech1.com/forums/showt...&highlight=386

[Tepco]

Yes, you messed up coil calculation, but never mind, will work even with that coil. This explain bit higher current consumption, fix coil issue later. 4066 (U7) is properly oriented (otherwise you wont get correct 5 and-5V), best you can do is to troubleshoot using what you already have, multimeter and piezo. With multimeter, check U3 pin7 DC voltage, and variation of it when large metal is present near the coil. Also check U3 pin 1 voltage, and how it varies with threshold adjustment. But before this, disconnect piezo from circuit, connect one end to battery -, with another end touch U4 pins 10,11,3,4, audible signal of varying intensity must be present, this will verify timing circuit operation, lack of any signal means malfunction. TX part around 555 and mosfet is apparently good, if audio is missing on U4 something around Q2 or components surrounding U4 can be wrong, if dc voltages on U3 are good, something is probably wrong around audio output, Q6 and nearby components. Make these tests and post results.

[kasperfish]

Thank you for the great help guys. I really appreciate your help! I wound a new coil with approximatly 0.300mH inductance. The power consumption is slightly different now (as already suggested by tepco). The machine was on for about 20 minutes without components getting hot. I did try getting 0V at U2 pin6 by turning the offset trimpot. 460 mV is the lowest I can get. While this is not much, it isn't 0V. Can this be an issue?

consumption with coil

tuning up: 60mA
tuning down: 50mA

consumption no coil

tuning up: 30 mA
tuning down: 19.88 mA

I also did the tests suggested by Tepco, here are the results...

DMM test
-------------

U3 pin7
no metal: 113mV
with metal (iron hammer): +180mV

U3 pin1
tuning up: 0.62V
tuning down: 3.26V

Piezo test
-------------
U4

pin10: continuous high and loud
pin11: continuous quite and lower
pin3 and pin4 sound the same but different then 10 and 11

I also tested pin 3 of the 555 and the sound is different from U4 pin4

So can I conclude that there is something wrong with the timing as the sounds aren't varying in intensity?

[Tepco]

Certainly something about audio output, everything else looks good. Measure DC voltage at Q6, E,B, C, and how it change with threshold adjustment. DC control voltage goes from U3 pin 1, via R23, D3, chopped by U7, analog switch between pins 10 and 11, to produce audio output. Tuning up or down (changing threshold adjustment) produce some change in current consumption, this is normal, so something may be wrong around P4 volume adjustment, or U7 fail to chop audio signal. Probably minor issue, bad connection, P4 trimmer or PCB track failure etc, you can check with piezo for very weak signal at Q6 B and full output at C.

[kasperfish]

Hi tepco,

the detector is working! It isn't very sensitive yet, but it is working! I resoldered the connections from te volume pot.... and that did the trick. Thank you for your help! I go out for a search trip now but will do more tests this evening. Thank you again!

[kasperfish]

Hi all,

I made a short movie from my surf pi in action. Like I said it isn't sensitive yet but I'm already pretty happy with the result. Next thing to do is trying to boost the sensitivity and thinking about the housing of the detector. I'll keep posting my progress here.

peace

[geoscash1]

kasperfish, Was that a cell phone you were using to wave over your coil ????

[kasperfish]

hi geoscash1,

no it was an aluminium card holder.

[geoscash1]

Ok, lol....

A buddy of mine was over last week when I was testing mine and I told him to wave something over my coil for me and he used his cell phone, his phone didn't work for 2 days after that and is still messed up...lol

what size of coil did you make ?

[chemelec]

It Possibly Erased the Chip.

[golfnut]

did you tune the two blue trimmers about to get best performance?