My DIY project DIY Wiring

[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]

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.

[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 ...

[Qiaozhi]

Here is a picture of what i am getting out of my Q3 with the coil on.

It almost looks like whats in the pdf hammer head scope pictures, but theres still a sort of square wave to it on one side .

Also there is a little wavy look to the spikes when you see a few on the scope together ,is that the ringing i have read people talking about ?[ATTACH]27787[/ATTACH]

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.

[davros]

Here is a picture of what i am getting out of my Q3 with the coil on.

It almost looks like whats in the pdf hammer head scope pictures, but theres still a sort of square wave to it on one side .

Also there is a little wavy look to the spikes when you see a few on the scope together ,is that the ringing i have read people talking about ?

[davros]

That should be the peak flyback voltage, you can only see this on an oscope.

Oh ok ! i will look on my little scope .
I was getting worried as it didn't look good on the multimeter .

[Carl-NC]

Sorry about that Carl my lap tops screens fussy at times ,bad video chip perhaps bit like how my eyes and brain are these days .

Another Question perhaps you or others could answer .

On Q3 should i be getting a voltage between 200v to 400v across the coil ,is this AC i should be testing for ?

That should be the peak flyback voltage, you can only see this on an oscope.

[davros]

The outputs of the sampling integrators are DC levels that vary with target proximity. There is no waveform (except noise) unless you sweep a target over the coil.

A little more use of capital letters and punctuation would make your posts much easier to read!

- Carl

Sorry about that Carl my lap tops screens fussy at times ,bad video chip perhaps bit like how my eyes and brain are these days .

Another Question perhaps you or others could answer .

On Q3 should i be getting a voltage between 200v to 400v across the coil ,is this AC i should be testing for ?

[Carl-NC]

The outputs of the sampling integrators are DC levels that vary with target proximity. There is no waveform (except noise) unless you sweep a target over the coil.

A little more use of capital letters and punctuation would make your posts much easier to read!

- Carl

[davros]

Spent today working on stage by stage fault finding ....
Made part of it work so far , i had to replace R6 with a 100 ohm resistor i got no signal till i dropped that 10k with my resistor wheel ....had no real problem with Q2 but Q3 i ended up replacing with a scrapped bipolar NPN transistor C4544 i had handy its rated at 300 volts and seems ok in this circuit the wave forum is like a large square wave with a spike one side of it not sure its correct R11s 680ohm i tested it can be a large range i notice below 100 ohm wave form changes more to a spike like .
The 74hc221s are working fine the tranys after those feeding the 4066s...as for the op amps i am not sure ...Had also trouble with the VCO..... one of the hammer head schematics theres no resistor between pins 7 and 8 till i spaced one there it was dead also .
Now its going theres a tone but no real change so something is still up with the opamps or perhaps the 4066 switches .
I know there are a few scope shots of some of the early stage test points but are there shots of where should be correct wave forms from the op amps and 4066 so on ?
Can you see the coil receiving metal object on your scope after the first op amp hard to tell if those buggers are working ?

[davros]

So thats where i am at today just need a little time and get these holidays out of the way to work on it more ...
Doing point to point wiring for me is fun i enjoy that more than a brought circuit board but i do have to say i had to really think about the wiring with so many different power rails .

Doing it my way you can change things and parts size of boards to a point ,its been fun so far and i hope it works fingers crossed ! well from a friend who worked in electronics once said to me if it doesn't work make it work even if you have to change things .
i will keep those interested updated on the project

[davros]

Now i am at the point of testing fault finding and such also doing the panels the signal for the coil is via that N connector that down converter the can and N connector still handy ...i want to bracket the case to the shaft .
Also i want the shaft to be taken apart for trips as thats easier than taking some thing the size of a wipper snipper on holiday .

[davros]

Now the idea for the shaft i think i have said before i like the crutches at first all i could find were the older type so i worked with that to see what i could come up with but i did end up finding one pair of the type with the arm rest so i can go either way ...they are very cheap at 5 dollars a pair at all my local reuse shops at the dump.
i have been told to make the bottom out of pvc ...i found some nice sized and strong plastic boat oars which i can cut to size and tack on to the crutches .

i am still thinking about the brackets and fixing bolt and nut for coil as these have to be nonmetallic i suppose ?So the bracket and bolt and nut might be harder to find

[davros]

Ok i will try and post a few more pictures here showing the boards and its evolution

[davros]

Ok that seemed to work the about pic 2 is how i started it i used an old pay tv down converter case scrapped the electronics and cut some PCB to size for point to point wiring as i want it to fit in this case and i have no problems following schematics

I have changed the power supply using a MC34063 DC to DC Converter IC it runs at a higher frequency and it can either convert up or down and out put either a positive or negative voltage also has a higher rate input voltage ...and there is no need for the 7805 regulator ...they run at 5 dollars if you got 3 you could do away with all the regulators perhaps ....i have a few 7905s so still used those ...