I didn't need another project -

[Ferric Toes]

Two jobs done so far. First was to change the 7 cell Nicad pack for something better and lighter. Now I use 3 Li-ion cells which are half the weight and much bigger capacity. I've used protected cells to avoid draining them if the detector is inadvertently left switched on. Charging circuit needs to be changed too. The electronics at the moment draws 150mA so the added capacity will allow running at a higher rep rate to speed up the response which is a bit slow at present. TX pulse width is 200uS so I will look at increasing that too. Mosfet will be changed for one with a lower Rds.on and a series diode. I will remove the IC's from the RX chain and put in sockets so that alternative devices can be tried. Several other things could be changed but this will do for the present. Oh yes, I changed the twisted wires from the coil socket to a miniature coax. The problem with this case is that the connector is on the bottom and very close to the pcb pads for the coil. To withdraw the electronics for testing then requires a long internal cable if the same connector is to be used.

For Vadim18 input resistor 1K and feedback resistor 1000K for OPA37. For KT315, sheet too large for my copier and out of date with 3055 TX and 709RX.



Eric

[kt315]

For KT315, sheet too large for my copier and out of date with 3055 TX and 709RX.
---
thank you. you can hang up the sheet on vertical wall, choice a sunny day and camera has to be >12MP. i did so. vertical wall was a bus stop.

[Vadim18]

Thanks Mr. Eric.
I'm not shure, but isnt it be a good for future modifications to lower feedback resistance say to 100k and compensate overall amplification at dc amplifier by x10.
Just so good op amp and feedback resistance is not optimised for it noise performance.

[eclipse]

Where can I find these waterproof potentiometer shafts? Looks to be a standard part I have the same on the JW Fishers 8X.

[Ferric Toes]

Where can I find these waterproof potentiometer shafts? Looks to be a standard part I have the same on the JW Fishers 8X.

The part in the red box is purely a flexible shaft coupler. The primary seal is the ring which sits in a groove within the top plate to the left of the red boxes. The 1/4in shafts from the knobs and into the couplers are stainless steel, but it does not matter what metal the actual pot and switch shafts are made of. Could even be plastic. There is an additional seal between the control knobs and the outer surface of the top plate which consists of a nylon washer under the knob and an O ring against the top plate surface. How the O ring groove in the top plate holes are machined I do not know. It also appears that those three O rings are square section.

Eric.

[Ferric Toes]

Thanks Mr. Eric.
I'm not shure, but isnt it be a good for future modifications to lower feedback resistance say to 100k and compensate overall amplification at dc amplifier by x10.
Just so good op amp and feedback resistance is not optimised for it noise performance.

I fully agree. I am going to remove all the Rx IC's and replace them with sockets so that better devices can be used. If possible, I might rewire the OPA37 to take a dual opamp. This would help optimise the front end better. I certainly want to bin the 741.

Eric.

[6666]

The part in the red box is purely a flexible shaft coupler. The primary seal is the ring which sits in a groove within the top plate to the left of the red boxes. The 1/4in shafts from the knobs and into the couplers are stainless steel, but it does not matter what metal the actual pot and switch shafts are made of. Could even be plastic. There is an additional seal between the control knobs and the outer surface of the top plate which consists of a nylon washer under the knob and an O ring against the top plate surface. How the O ring groove in the top plate holes are machined I do not know. It also appears that those three O rings are square section.

Eric.

Those flexible shaft coupler's are also used on 3D printers if you search on ebay on
"3d printer couuplings" you will find lots of all sorts and cheap, you can drill them out to match the pot shaft.

[Qiaozhi]

Those flexible shaft coupler's are also used on 3D printers if you search on ebay on
"3d printer couuplings" you will find lots of all sorts and cheap, you can drill them out to match the pot shaft.

I thought I'd seen those somewhere before. Here's one on my Geeetech i3 Prusa.

[Ferric Toes]

I have made some progress on updating the electronics while keeping the circuit board the same. First, I measured the various pulses, which were as follows.
Tx width 215uS
Tx rate 106pps
Delay range 20 - 118uS
Sample widths 20uS
Delay to second sample pulse 230uS measured from start of first sample pulse.
Inverter frequency for +5V rail 84.6kHz. A different circuit was used to my original.

Also noted was the the Rx amp had not fully reached zero until 50uS, so the first sample was on the slope prior to full recovery. The detector still worked OK at 20uS by adjusting the threshold control. This was the case both with the Garrett coil and one of my latest fast shielded coils. Also no different when the OPA37 was changed to a NE5534. This was found to be partly due to the 150 ohm resistor used for damping. EF performance was not the best when tested with a ferrite magnet waved over the coil. This is due to the capacitor ahead of the integrator only being 0.1uF I used a 22uF tantalum capacitor in the prototype. This was pointed out to Garrett at the time but they stuck with the 0.1uF for some reason not disclosed.

Another interesting feature is that the Tx Mosfet gate is coupled to the 555 timer o/p directly via a 10nF capacitor and that the gate/source resistor is whopping 150K. Trying a couple of other Mosfets did not work. I then found that the RFP8N18L is a Logic Level device that switches at lower gate/source voltages. Looking at the Tx waveforms it appeared that the drive was still not switching the Mosfet fully. Swapping the 10nF cap for 330nF cured the problem and I reduced the gate/source resistor to 100K which gives very clean Tx waveforms with a sharp rectangular 5V gate drive pulse. The RFP8N18 avalanches at 225V which flat tops at that level for 4uS before decaying via the damping resistor which has been increased to 560ohms. Also a HER208 diode now isolates the coil from the Mosfet Coss.

The gain of the Rx amplifier has been halved by using a 2K input resistor, and as been suggested, the gain can be made up later in the receiver chain. At this stage I have not incorporated a two stage preamp, but comparing the OPA37 and a NE5534 in this circuit, the 5534 recovers about 5uS quicker.

More to come later, but the upgrading of the XL500 is going well.

Eric.

[ivconic]

If you don't eventually offer a schematic with all your upgrades... than "...I didn't need another project..." can be translated to "...we didn't need another project here..." with much more sense.
Decide on this, would it be project to share among members here or something that will just fulfill your days against boredom and kept undisclosed.
Sad to notice; i haven't seen much from your work completely disclosed and documented well, on this forum, done by yourself.
Usually is reverse engineering done by somebody else.

[kt315]

garrett deposited. whole pocket of files. no secret files. if we are back to matter ok we are back.

http://depositfiles.com/files/9ru2lph3g

[Ferric Toes]

If you don't eventually offer a schematic with all your upgrades... than "...I didn't need another project..." can be translated to "...we didn't need another project here..." with much more sense.
Decide on this, would it be project to share among members here or something that will just fulfill your days against boredom and kept undisclosed.
Sad to notice; i haven't seen much from your work completely disclosed and documented well, on this forum, done by yourself.
Usually is reverse engineering done by somebody else.

That is a tad cynical in my view! For well over 20 years I have shared information by the means of forums on the technology side of metal detectors. This was because I was not happy about the secrecy that was general at that time in the detector industry as to how their products worked, particularly PI as that was my speciality. However, copying a product by means of reverse engineering was always a problem, not so much with hobbyists, but with other manufacturers. What is the point of developing something and putting it to market, only to find that a copy is on the market a short time later and eroding one's own sales. This comment does not include reputable manufacturers such as the likes of Garrett, Whites, CScope, Detectopro.That negative aspect has always been there, and always will be there unless you spend a fortune and patent as much as possible as some do today. As reverse engineering is a fact of life, I have rarely made public any complete circuits. Why would I want to hand it out on a plate? Some people love the challenge of reverse engineering, so why should I deprive them of the opportunity to do that. It is alive and well today and with genuine hobbyists, I don't have a problem.

Regarding the Garrett XL500, the circuit as I developed it is already on this thread,so there is no point in repeating it.(post 3 attach 2,3. The latter being an update) Garrett's official circuit, dated 28th Jan 1983 I have a copy of, but it is not the same as the 1989 unit I have and also departs further from my original design. It does say on the sheet 'Proprietory Notice - This information is the property of Garrett Electronics Inc, and shall not be copied or reproduced for the purpose of sale or manufacturing of apparatus, except by written permission of Garrett Electronics'. You may say that it is now an old design and doesn't matter. I could write to Garrett's for permission but the people I dealt with are no longer there. They may say it is OK but there is little point as it is not the latest version with Mosfet Tx and better opamp at the Rx front end. The board layout has not changed, as far as I can see, since 1983, so the modifications that I am doing will be relevant.

I still have a way to go with all the updates that I would like to see, and when it is done then the full information will be made available. I'm not sure how much interest there is, but since 1983 and 1991 a lot of XL500 and XL200's must have been sold. These detectors are very rugged and ideal for both shallow and deep water hunting. With uprated performance; longer lasting and lighter batteries, they should be good for a few years yet.

Meanwhile I will disclose information as I do the various stages so that others can comment and offer advice and suggestions if they wish. I would like to find a better logic level Mosfet than the RFP8N18 with higher avalanche volts and lower Rds.on. There is no boredom in my neck of the woods. I already had two projects going which are suffering a bit as a result of acquiring the XL500. But it was hard to resist getting the detector when it apeared to be in good shape and I knew it would be relatively easy to upgrade.

Eric.

[kt315]

It does say on the sheet 'Proprietory Notice - This information is the property of Garrett Electronics Inc

---
give me this sch and i will delete it in PHOTOSHOP. a job on 1 minute.
while cool story and too pathetic. i just reminder you Eric now... Colonel Phil Corso HAD
gave all info before he gone. so Remember about The Death. do our hobby best.
you should garrett nothing btw... because sir Garrett had gone.

[ivconic]

"...That is a tad cynical..."

Supposed to be.

"...I have rarely made public any complete circuits..."

That was my point indeed.

"...Why would I want to hand it out on a plate?..."

It is always much better when it comes from author than from a third party. One (even hand drawn) schematic speaks much more than 100 posts.
Instead of "i did this... i did that.." is much simpler, easier and better to post schematic.
You will spare many words like that.
Later on you can answer the questions if you like and if there are any.
So far i never saw author to do that on these forums. Except Carl. He is indeed unique exception (Hammerhead and few other articles that he did).

"...I will disclose information as I do the various stages so that others can comment and offer advice and suggestions..."

Alright. But without schematic it will be again numerous textual posts diluted by various distractive questions and opinions from others.
What we need here is solid ground. The schematic. Of all what you wrote about in your previous post.
Hand drawn, no problem, later taken photo of it by camera on your phone.
...
Be second in history of MD forums to do something like that (counting Carl as first one).
Overall i mean nothing derogatory about you and your work, on contrary!
Take this as small advice. If i may dare to offer it to you.
Cheers!

P.S.
Take my word on this; reverse engineering i can do.
But i never enjoy it. What would make me happy is to see author to do all the work for forum instead.

[ivconic]

It does say on the sheet 'Proprietory Notice - This information is the property of Garrett Electronics Inc

---
give me this sch and i will delete it in PHOTOSHOP. a job on 1 minute.
while cool story and too pathetic. i just reminder you Eric now... Colonel Phil Corso HAD
gave all info before he gone. so Remember about The Death. do our hobby best.
you should garrett nothing btw... because sir Garrett had gone.