My DIY project DIY Wiring

[davros]

That's the correct waveform you should get across the coil. The "sort of square wave" is the coil "on" time. This is the time during which current is building up in the coil. When the transmit pulse turns off, the coil exhibits a high flyback voltage. This voltage will exponentially decay to 0V, and the correct value of damping resistor will critically damp the decay (no ringing).
I suspect the wavy look you refer to is mains noise pickup. If you rotate the coil you will see this noise change amplitude.

OK thats good to know then ,that makes me happy that up to there in the circuit is working
That sort of makes sense on the wavy look to the spikes sort of not all at the same levels , i am testing with a power supply might be picking up the main frequency....
I spent the afternoon making sure i had not made a mistake on the receiver part on ic6 i have made a mistake in powering R21 to -5d instead of -5 7905 regular,apart from that the wiring looks good on that ,i will change that tomorrow .
I will also move the coil around and watch it on the scope ...

[davros]

I am just testing my coil which was wound for another metal detector project just handy to use on this.
Used it in circuit for that scope picture a post or 2 ago ,well its 70 turns 5 ohms the inductance is 2.3mH which i think is 2.300uh bit over to say the least whats asked for in the project .
I am not sure what effect this would have on the circuit as in its to large a value.
If any one knows one way or the other if its not worth testing with i will rewind another coil for testing.

[Thomas]

For the fixing bolt and nut for coil, I noticed in the plumbing section some of the hardware for toilet seats is made out of nylon. Nice response on the scope shot.

[davros]

For the fixing bolt and nut for coil, I noticed in the plumbing section some of the hardware for toilet seats is made out of nylon.

Hi Thomas
The bolt nut and bracket for the arm i am finding the hardest to track down ,i would need to bolt the bracket down as well so thats a problem ...
I looked in the plumbing section of Mitre 10 and i did see the toilet seats plastic bolts nut but i have not seen a nylon one if they are about we do have other hardware stores to check .
I suppose since theres a lot of DIY metal detectors out there my problems been dealt with ,i am not up to that part of it yet more getting my electronics working and thinking about that part when i get up to it .

[TH'r]

Hi Thomas
The bolt nut and bracket for the arm i am finding the hardest to track down ,i would need to bolt the bracket down as well so thats a problem ...
I looked in the plumbing section of Mitre 10 and i did see the toilet seats plastic bolts nut but i have not seen a nylon one if they are about we do have other hardware stores to check .
I suppose since theres a lot of DIY metal detectors out there my problems been dealt with ,i am not up to that part of it yet more getting my electronics working and thinking about that part when i get up to it .

At last resort White's might sell you their 3/8" nylon coil bolt and nut (#802-5096-11). They offer them to US customers @$1.50.

[Thomas]

2 bucks

[6666]

minelab distributors will sell you a bolt

[davros]

Thanks guys for the help on the bolt ,still have to have a good look around before start to worry ! i will ask 6666 if i can't track one down.

I spent the weekend redoing part of the power supply i stuffed up on the positive ground side of it ,i checked the dual supply side of things across the ics that use it and i had got it wrong no other way of putting it .

So i tried this idea the the transistor rail splitter but i lost voltage after the regulators .


I then tried another more simple floating ground with just 2 4.7k resistors 2 caps ,that seems much better .



I have tested it on the circuit replacing the the transistor version in my drawing and it seems ok now but have not tested the signal outputs of the ics that use that dual voltage part of the power supply .

If it gives me any more grief i will just use 2 batteries .


I did have to rewire things a little to use this power supply its not to different .

Yes Thomas that little scope is pretty handy not only a scope be a frequency meter ,smaller than a i phone charges via a usb cable.

[Thomas]

I then tried another more simple floating ground with just 2 4.7k resistors 2 caps ,that seems much better .

rdiv.png

Simple is the way, with regs following, when the battery(s) get weak, everything stays close to balance.

[davros]

Simple is the way, with regs following, when the battery(s) get weak, everything stays close to balance.

Yep Thomas i suppose you are right there ,trial and error seems this was the way to go .

Have to go out to night but i hope to test ic6 tomorrow and the expected voltages at pin 6 ...last time i tried i found out i stuffed up one half of the 5 volt part of it ...i will never complain about a dual power supply again .

[davros]

Another Hammerhead is born testing it now seems to work .
I think i need to get it away from my table and any other metal objects to adjust it right ,have not even put the foil around the coil and its giving good results .
Now back to the rest of it .

[davros]

I am casing up today i had to change the speaker circuit a little as i am using a metal case and the coil plug ground and head phone which was on the negative battery as its ground causing a short ,just using Q7 after the 555 vco so it was easy to swap things around on that transistor.

I also wound a coil to the correct size and number of turns today ,all in all very happy with results .

Will be able to bracket it on the shaft soon.

[Qiaozhi]

I am casing up today i had to change the speaker circuit a little as i am using a metal case and the coil plug ground and head phone which was on the negative battery as its ground causing a short ,just using Q7 after the 555 vco so it was easy to swap things around on that transistor.

I also wound a coil to the correct size and number of turns today ,all in all very happy with results .

Will be able to bracket it on the shaft soon.

You can also use a headphone socket with a plastic bezel.

[davros]

You can also use a headphone socket with a plastic bezel.

Hi yes thanks i did think of that but i had none handy that were screw and nut types just the type you solder on board and are placed via a hole .
The slight circuit change wasn't to much of a problem.
I am thinking of a housing for the coil at the moment , don't want to be embarrassed talking it out passed the back yard if you know what i mean ; ).

[Silver Dollar]

I've seen 10 1/2" housings on Ebay for $14 but they come and go. Right now there's one for $21

This one says 2 pc. Not sure if that's top and bottom?
http://www.ebay.com/itm/2-pc-metal-d...item1c3b2132d7

This one says 5 pc for $38
http://www.ebay.com/itm/5-pc-metal-d...item1c3b213570

I ordered the $14 one here. But have not received it yet;
http://www.ebay.com/itm/121244086142...84.m1439.l2649

Come to think of it, I ordered 2 for $14 each maybe I should have ordered the 2 pc for $21?