Myers Depot Metal Detectors

From centech, to... this:

It seems that the older cell phones that I've dissected have the external CW. He asked for a description and I gave him one that he will most likely find in the old cell phone in the junk drawer. :grin:
 
Another source for the little motors are from Gillette sensor vibrating razors.
 
The writeup is here

I haven't been able to get this 100% the way I want. However, I have compiled a writeup on how to add range detection to the centech pinpointer.

https://docs.google.com/open?id=0Bzyrcq4havSaQk9aTEJ4c0JST1d6SkJfSG5VWHdwZw

I realized that if I waited until I had this "perfect" it might never get completed, and that would be a shame. This will allow you to get as far as I've gotten - these instructions talk about putting in a headphone jack, but you can substitute with a speaker if you want.

Please let me know if I've left anything unclear in these instructions, and I'll try to clarify the document.

V

edit: if you're having trouble with that link, there's a pdf version of it, here:
https://docs.google.com/open?id=0Bzyrcq4havSaU0htQ0JjS3BTVzItTHBuRll1aXlMdw
 
I'm downloading the PDF right now, 30 minutes... Kind of what I expected, 555 wired as a VCO, but wonder where you took up the input off the Centech board. The big speaker is going to be a current hog, will drain a 9 volt pretty quick. Didn't take note of which 555 version you were using, but the standard will sink/source 200 mA, probably why it wasn't very loud. A peizo speaker would give louder output at that current, but you need to use on that's got a plastic enclosure, which provides a resonant cavity. I can provide links to some electronics surplus sites I've bought from many times, that have several to choose from, their cheap, dollar or so. Shipping might hurt some though. They can be found in older equipment pretty often. Lots of the newer stuff I've salvaged have the oscillator built in, like the one the came in the Centech. There are little powered speakers, for media players (iPod types), for a couple of dollars, probably have these type in them as well, cheap and available most every where.

Looked at the parts list, and it's the CMOS 555 version, only 100 mA (I think), been a while, pretty much stopped using them when I started playing with microcontrollers. You could probably use a pair of transistors, as a push-pull amplifier, and get more volume, but think a magnetic coil speaker is going to be a big draw on a 9 volt battery.

Looks good, and will be giving it a shot. Might not do it the same way, but close enough. Wish you would have put this up Friday, wouldn't have even been tempted to order the ProPointer. Least I'll be able to compare the two. Would be amusing, if this mod takes the Centech pretty close, for a quarter of the price. Still like the probe on a cable, will allow me to keep digging smaller diameter holes, and go deeper. It's loose sand around here, just need enough room to stick my hand in. Wonder just how big the coil is, inside the probe? Maybe fingertip size?
 
HarveyH48 said:
I'm downloading the PDF right now, 30 minutes... Kind of what I expected, 555 wired as a VCO, but wonder where you took up the input off the Centech board. The big speaker is going to be a current hog, will drain a 9 volt pretty quick. Didn't take note of which 555 version you were using, but the standard will sink/source 200 mA, probably why it wasn't very loud. A peizo speaker would give louder output at that current, but you need to use on that's got a plastic enclosure, which provides a resonant cavity. I can provide links to some electronics surplus sites I've bought from many times, that have several to choose from, their cheap, dollar or so. Shipping might hurt some though. They can be found in older equipment pretty often. Lots of the newer stuff I've salvaged have the oscillator built in, like the one the came in the Centech. There are little powered speakers, for media players (iPod types), for a couple of dollars, probably have these type in them as well, cheap and available most every where.

Looked at the parts list, and it's the CMOS 555 version, only 100 mA (I think), been a while, pretty much stopped using them when I started playing with microcontrollers. You could probably use a pair of transistors, as a push-pull amplifier, and get more volume, but think a magnetic coil speaker is going to be a big draw on a 9 volt battery.

Looks good, and will be giving it a shot. Might not do it the same way, but close enough. Wish you would have put this up Friday, wouldn't have even been tempted to order the ProPointer. Least I'll be able to compare the two. Would be amusing, if this mod takes the Centech pretty close, for a quarter of the price. Still like the probe on a cable, will allow me to keep digging smaller diameter holes, and go deeper. It's loose sand around here, just need enough room to stick my hand in. Wonder just how big the coil is, inside the probe? Maybe fingertip size?
Click to expand...

Please, take this and run with it!

...then tell me where you got to. :)

The pictures show a huge speaker, but the explanation is actually just for putting in a headphone jack. I tried a few different speakers and buzzers I had laying around, and nothing seemed to give me much volume, even when I used the output of the LMC555 (50mA output) to drive the FET, opening up the full 9v from the battery. Just couldn't get any decent volume. If you find a setup that makes more noise, PLEASE share it!

I actually found someone on my hometown CL selling a used ProPointer, which I had a buddy pick up for me. So I'll soon have both to compare, too. :)
 
There's the LM7660 voltage doubler, 8-pin dip, like the 555. I haven't messed with FETs, unless I really need the power. Most need 10 volts to fully turn on. The gate also needs to discharge, before it will turn off. Might be things that are getting in your way. Not something I've used much, so may not apply. Not sure how soon I'm going to get to this, kind of into the LG TV, I found yesterday morning.
 
I'm not good with resistor colors. :no:
Please verify resistors used in 5 color resistors. :research:

10k
brn blk blk red

100k
brn blk blk org

47k
yel vlt blk red

10m
brn blk blk grn

Thanks
 
10k brown black orange

100k brown black yellow

47k yellow violet orange

10M brown black blue

I memory servers me right

Big Boys Race Our Young Girls But Violet Generally Wins
Blk Brn Red Org Yellow Grn Blu Vio Grey White
0 1 2 3 4 5 6 7 8 9
 
pan4au said:
10k brown black orange

100k brown black yellow

47k yellow violet orange

10M brown black blue

I memory servers me right

Big Boys Race Our Young Girls But Violet Generally Wins
Blk Brn Red Org Yellow Grn Blu Vio Grey White
0 1 2 3 4 5 6 7 8 9
Click to expand...

Thanks for the reply.
The mixed pack of resistors I have are 5 color, so I will differ a bit from 4 color. The 4th color is the multiplier and the fifth is tolerance I believe.
I wonder why it's done in different numbers of bands?
 
Resistors manufactured for military use may also include a fifth band which indicates component failure rate
 
The schematic only shows one 100k r, but the circuit board pic shows
two 100k r.?

Could you show a larger pic of the schematic. Some portions were cut off.
Thanks
 
sorry about the delay! I've been on vacation, and forgot all about this.

here's a pdf of one possible configuration
 

Attachments

  • Centech pinpointer scematic.pdf
    17.8 KB · Views: 423
Has anyone made any headway it getting the buzzer speaker to have full volume yet? anxiously awaiting a solution....
 
Valhad said:
sorry about the delay! I've been on vacation, and forgot all about this.

here's a pdf of one possible configuration
Click to expand...


Has anyone else hooked up this configuration? (Pin 3 from the 555 timer input into the gate of the FET to drive the Piezo). I am getting a solid tone at all times when the button is pushed. Not sure what is wrong at this point.

The original video shows some type of buzzer / externally hooked but I can tell what type and how its hooked.

I am hoping to get to the point of the video in the first post where I hear a clicking tone at a frequency based on distance.
 
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