Mirage PI Project, anyone interested?

[SVEN1]

The speaker volume is very low with an 8 ohm speaker - even if the 10 ohm series resistor is bypassed. What workaround do you recommend for this?
Should be plenty loud, might try swapping out the 3906?

I also want to add the auto-track freeze feature as per the Hammerhead design. Do I simply cut the track and put a switch between pin 5 of TL072 and the 220k Sat Adj resistor?
Do you mean a static pinpoint? Originally there was such a feature on the original circut board versions. It was removed, we felt it was needed. You can add it back in, it basically switches SAT to min. setting. You will have to rework the PCB you have, see pix, can then add a toggle switch or a normally on type push button switch wired to the solder pads marked PP.

[Elliot]

The speaker volume is very low with an 8 ohm speaker - even if the 10 ohm series resistor is bypassed. What workaround do you recommend for this?
Should be plenty loud, might try swapping out the 3906?

I also want to add the auto-track freeze feature as per the Hammerhead design. Do I simply cut the track and put a switch between pin 5 of TL072 and the 220k Sat Adj resistor?
Do you mean a static pinpoint? Originally there was such a feature on the original circut board versions. It was removed, we felt it was needed. You can add it back in, it basically switches SAT to min. setting. You will have to rework the PCB you have, see pix, can then add a toggle switch or a normally on type push button switch wired to the solder pads marked PP.
[ATTACH]45845[/ATTACH]

Thanks Sven. So for the static pinpoint function, you're effectively just placing a switch where shown in the attached image.

I'm also curious about why the earth point near the SAT adj pot (and one other corner mounting point on the pcb - i.e. bottom left corner when looking from the top side) isn't connected to earth on the pcb. The machine works well without these points connected to earth. Are you assuming the the pcb is mounted in a metal box and the earth points are connected via metal stand-off posts?

[SVEN1]

Really need only one PCB mounting bolt to ground to metal case. We only use three as we originally only had three mounting holes due to lack of room on earlier version boards. After shifting parts around during revisions, it allowed enough room to put the fourth mounting hole on the board.


In this case, used a Vintage Garrett, the grounding plate was a copper clad one sided PCB board as the Garrett case was plastic. I have also used a solid copper plate as a grounding plate in other plastic enclosures. If using a metal box, ground the PCB directly to it using metal stand-offs.

[SVEN1]

To all those reading this post and have inquired about obtaining a PCB.
I no longer have any left for sale.

Just a note there are some unofficial copies made, of the Mirage PCB floating out there, it does not completely resemble any PCB versions I have personally made up.
If you didn't get the PCB directly from me, probably a copy and if you build it and it doesn't work, take it up with the person who sold it to you.
One copy I saw had a large 1000uf electro capacitor near the upper right corner of the PCB.
No Mirage PCB has an electro cap of more than 100uf.

[Elliot]

Hi All. I purchased what I was advised were the last two PC boards off Sven just recently. I have made one up, and am fine tuning it as I write. The board has a few things that I want to modify to better fit components (e.g. several trim pots had to sit above a resistor due to them being too close together for the trimpot I used); there was a superfluous wire link position (carry over from previous mods no doubt), I wanted the option to use detachable wire connectors for the main pots (not be restricted to just solder joints), and I wanted to add the following features:

- 3 way selectable Centre frequency switch (for potential pesky high EMI sites),
- Differential amplifier boost switch (+20% gain),
- Main Amp gain switch (bypasses the 1k that was added back in later versions),
- SAT hold switch (for when pinpointing) and,
- a good 'ol volume control!

The bulk of these are for maximising flexibility in the field, when choosing between operating performance and/or stability, without having to rip the machine apart every time you want to tweak something.

I have spent considerable time designing the modified PCB using Pcbnew (using a two layer FR4 PCB due to all those pesky wire links), and will organise a prototype board to ensure all is working fine before I order any more boards (and, NO, I haven't used a 1000uf electro like someone else sounds like they've done lol).

If anyone is interested in purchasing a board in due course with my mods, let me know, and I'll order a batch to suit (PS: I'm in Australia).

[SVEN1]

Hi All. I purchased what I was advised were the last two PC boards off Sven just recently. I have made one up, and am fine tuning it as I write. The board has a few things that I want to modify to better fit components (e.g. several trim pots had to sit above a resistor due to them being too close together for the trimpot I used); there was a superfluous wire link position (carry over from previous mods no doubt), I wanted the option to use detachable wire connectors for the main pots (not be restricted to just solder joints), and I wanted to add the following features:

- 3 way selectable Centre frequency switch (for potential pesky high EMI sites),
- Differential amplifier boost switch (+20% gain),
- Main Amp gain switch (bypasses the 1k that was added back in later versions),
- SAT hold switch (for when pinpointing) and,
- a good 'ol volume control!

The bulk of these are for maximising flexibility in the field, when choosing between operating performance and/or stability, without having to rip the machine apart every time you want to tweak something.

I have spent considerable time designing the modified PCB using Pcbnew (using a two layer FR4 PCB due to all those pesky wire links), and will organise a prototype board to ensure all is working fine before I order any more boards (and, NO, I haven't used a 1000uf electro like someone else sounds like they've done lol).

If anyone is interested in purchasing a board in due course with my mods, let me know, and I'll order a batch to suit (PS: I'm in Australia).

Frequency control needs to be a multi-turn for fine adjustments. Selectable switch wouldn't even begin to cover the actual frequency needed depending upon conditions encountered. A single turn pot will work if your careful with making fine adjustments.

Many experiments were made using all sorts of amps, we settled what we had on the current version. Two stage amp mod was done, outcome was poor, switched back to a single stage early on.
Main amp switch to switch the 1K out and in will not work, has been tried, you will encounter feedback etc. Its either jumper or resister. We changed some other resistors to increase gain but, found the circuit was becoming unstable and harder to keep in tune.

SAT , a pinpoint switch was originally designed in. The pinpoint switch just reduced SAT to min. for a non-motion type pinpoint. Because the Mirage was so easy to pinpoint at 75% SAT setting, the pinpoint switch was not needed. Just stop the coil on top of target, let it retune, give a small wiggle and the target has narrowed, do it again if needed. Target will be in the coils center. By the time you use the PP switch, another person will have pinpointed the target and be on the ground digging.

Volume control was not placed on the PCB as you just wire the pot in......in our case, we use volume controls in our headsets and we rarely used the speaker on the control box. Mostly for demonstrations.

We used a lot of jumpers, since it was easier to work on a single sided board when making circuit board changes-revisions for testing purposes. A 2 sided board was considered for a final version. Just never happened. A SMT parts version was also considered, just too hard to build for the average builder, so it never happened, plus it meant buying a whole pile of SMT parts. We already had a pile of thru-the-hole parts...

There are a number of Geotech Forum members that have built the Mirage, like any project some with much better success. Also, many have experimented with the circuit and may give you some more insight. I was fine with my current version to suit my needs and purposes. The beauty of the project is for those who are able to, go ahead and experiment, just keep in mind what I posted above. I have built over 50 Mirage circuit boards of different variations and will say some builds were much better than others depending upon the parts used and the tolerances of them and search coil build. Any complete Mirage detectors that I have built for others needed to have equal performance to my personal unit . If not the circuit board was scrapped.

Side note, when I use the 8.5" search coil, rarely need to use more than 25% Gain, goes plenty deep. 75% Gain is usually max used. The 100% Gain setting is there for those who feel the need to adjust that high.

Please remember the Mirage was designed around finding small gold and gold jewelry, at max. depth the circuit would allow. More of a niche detector. At the expense of finding higher conductor metals at greater depth. If your interested ins such, develop the Mirage more in line with Carl's Hammerhead as did George when he designed the CrossBow. I have always said the Mirage is at one end of the Rainbow and the CrossBow at the other, they can compliment each other.

Also, a new circuit board design a forked branch of the Mirage that has been worked on for a few years is now revamped over quite a few versions. Final outcome is superior to the Mirage. It has two audio versions, one sound more like a VLF and the other the standard tic-tic-tic. Samples down to 6us. Frequency can go back to a single turn pot, super stable rarely needs adjustment. Lots of parts and IC's added. As for performance, equals the Mirage for depth or slightly better and has better sensitivity to very tiny gold nuggets. I am not at liberty to produce these new boards or give out the circuit design, as it has propriety circuit design incorporated into it. But, can say there are several Geotech members who have gotten and built one of these new version boards and can attest to what I have written. My electronics friend who designed the original PI circuits from the Hammerhead, with the help of Carl M., Reg Sniff, Eric Foster. He should be working for a major metal detector manufacturer..... but, he is 84 years old now, retired electronics engineer and enjoying his private life, family and friends. Now he does keep his mind active by experimenting with PI designs.

The Mirage started out as just a modified Hammerhead built on a bread board. I was able to take the schematics and produce the first actual circuit boards back in 2013 after Ivonic took the schematics and layed out the first Sprint board design for us. The circuit was refined so many times since then. Now, will say one of the early designs worked excellent and easy for the DIY person to build. It was a perfect Pi for hunting trashy parks, schoolyards and picnic grounds with the 7" search coil.

[SVEN1]

Earliest versions were named Cobalt which eventually morphed into the Mirage.

[SVEN1]

This is one of my last builds, repurposing an old Compass Relic Magnum with one of the latest circuit boards with the VLF type audio. The just the machine to take to a club hunt and show them what an old detector can do. Looks like an old dinosaur VLF/TR but what's inside changes all that.

[bernte_one]

Hi Sven, you are an unfair Player or?

Put high tech in an old Cadillac Chassis

[SVEN1]

Hi Sven, you are an unfair Player or?

Put high tech in an old Cadillac Chassis

[kt315]

was done amigo.

[Goaty]

If anyone is interested in purchasing a board in due course with my mods, let me know, and I'll order a batch to suit (PS: I'm in Australia).

PM sent

[Elliot]

Frequency control needs to be a multi-turn for fine adjustments. Selectable switch wouldn't even begin to cover the actual frequency needed depending upon conditions encountered. A single turn pot will work if your careful with making fine adjustments.

Many experiments were made using all sorts of amps, we settled what we had on the current version. Two stage amp mod was done, outcome was poor, switched back to a single stage early on.
Main amp switch to switch the 1K out and in will not work, has been tried, you will encounter feedback etc. Its either jumper or resister. We changed some other resistors to increase gain but, found the circuit was becoming unstable and harder to keep in tune.

SAT , a pinpoint switch was originally designed in. The pinpoint switch just reduced SAT to min. for a non-motion type pinpoint. Because the Mirage was so easy to pinpoint at 75% SAT setting, the pinpoint switch was not needed. Just stop the coil on top of target, let it retune, give a small wiggle and the target has narrowed, do it again if needed. Target will be in the coils center. By the time you use the PP switch, another person will have pinpointed the target and be on the ground digging.

Volume control was not placed on the PCB as you just wire the pot in......in our case, we use volume controls in our headsets and we rarely used the speaker on the control box. Mostly for demonstrations.

We used a lot of jumpers, since it was easier to work on a single sided board when making circuit board changes-revisions for testing purposes. A 2 sided board was considered for a final version. Just never happened. A SMT parts version was also considered, just too hard to build for the average builder, so it never happened, plus it meant buying a whole pile of SMT parts. We already had a pile of thru-the-hole parts...

There are a number of Geotech Forum members that have built the Mirage, like any project some with much better success. Also, many have experimented with the circuit and may give you some more insight. I was fine with my current version to suit my needs and purposes. The beauty of the project is for those who are able to, go ahead and experiment, just keep in mind what I posted above. I have built over 50 Mirage circuit boards of different variations and will say some builds were much better than others depending upon the parts used and the tolerances of them and search coil build. Any complete Mirage detectors that I have built for others needed to have equal performance to my personal unit . If not the circuit board was scrapped.

Side note, when I use the 8.5" search coil, rarely need to use more than 25% Gain, goes plenty deep. 75% Gain is usually max used. The 100% Gain setting is there for those who feel the need to adjust that high.

Please remember the Mirage was designed around finding small gold and gold jewelry, at max. depth the circuit would allow. More of a niche detector. At the expense of finding higher conductor metals at greater depth. If your interested ins such, develop the Mirage more in line with Carl's Hammerhead as did George when he designed the CrossBow. I have always said the Mirage is at one end of the Rainbow and the CrossBow at the other, they can compliment each other.

Also, a new circuit board design a forked branch of the Mirage that has been worked on for a few years is now revamped over quite a few versions. Final outcome is superior to the Mirage. It has two audio versions, one sound more like a VLF and the other the standard tic-tic-tic. Samples down to 6us. Frequency can go back to a single turn pot, super stable rarely needs adjustment. Lots of parts and IC's added. As for performance, equals the Mirage for depth or slightly better and has better sensitivity to very tiny gold nuggets. I am not at liberty to produce these new boards or give out the circuit design, as it has propriety circuit design incorporated into it. But, can say there are several Geotech members who have gotten and built one of these new version boards and can attest to what I have written. My electronics friend who designed the original PI circuits from the Hammerhead, with the help of Carl M., Reg Sniff, Eric Foster. He should be working for a major metal detector manufacturer..... but, he is 84 years old now, retired electronics engineer and enjoying his private life, family and friends. Now he does keep his mind active by experimenting with PI designs.

The Mirage started out as just a modified Hammerhead built on a bread board. I was able to take the schematics and produce the first actual circuit boards back in 2013 after Ivonic took the schematics and layed out the first Sprint board design for us. The circuit was refined so many times since then. Now, will say one of the early designs worked excellent and easy for the DIY person to build. It was a perfect Pi for hunting trashy parks, schoolyards and picnic grounds with the 7" search coil.

Thanks Sven. The 3 way selectable Centre frequency switch will still utilise the multi-turn pot for fine tuning (10% frequency variance) for EMI. Instead of the standard fixed 68k centre frequency setting resistor, there will be 3 switchable resistors to choose from.

I note the comment about the 1k resistor ahead of the main amp. It may just end up being able to switching between 1k and other lower values if a wire link is too unstable. The aim to eek out every last little bit of performance, and to have it easily adjustable in the field to suit local conditions.

SAT - Fair comment, but pushing a latching thumb switch I would consider a bit quicker and easier for novices than the combined alternative actions you have outlined. I also tend to find that detuning means that you may loose depth. Did you ever try having a pinpoint switch that completely isolated the auto tuning function, instead of having a quasi (min auto tuning) pp function? I'm looking for a ultra low input bias current op amp to suit - not sure if the AD648 would well suit (just 10pA vs. 65pA for the TL072).

Jumpers - I completely respect the background, history and hard work to get it to where it is today! So thank you! When I assembled mine, I actually missed one of the tiny wire links, so I just thought I'd help prevent that from occurring again. Plus the IC sockets can sit better on the board.

I'm also contemplating tweaking the design to allow a 3 coil (1 x TX and 2 x RX) coil as in the Minleab Super-D search coil.

I'll have a look at the Crossbow and see if a switchable combination gold and treasure PI detector could be viable.

Sound Options - I also have been considering a switchable non-VCO and VCO version. I just need to see what extra components and circuit change need to be made.

New circuit board design - I'd love to try this other board that you refer too. It would probably save me a lot of unnecessary effort. Living near the Australian Victorian goldfields, this design sounds ideal for me! If you could separately pass on your friends details to me (friends willing that is), I'd be very grateful. You may still have my personal email address (last email from me was sent on 12 Feb 2019).

I appreciate the detecting community and the camaraderie and innovative thinking that it brings. If only politicians could collaborate just as well.

You can see how my current draft board rework is looking today (refer attached). I've so far managed to keep the same small sized footprint.

Happy detecting!

[dbanner]

This is one of my last builds, repurposing an old Compass Relic Magnum with one of the latest circuit boards with the VLF type audio. The just the machine to take to a club hunt and show them what an old detector can do. Looks like an old dinosaur VLF/TR but what's inside changes all that.

Looks really cool, nice!
Not sure how I feel about gutting an old detector just for the nice housing. Kinda like those old dinosaur machines kept stock.
Couldn't you have put it into an MD-4003 chassis instead?

[SVEN1]

Looks really cool, nice!
Not sure how I feel about gutting an old detector just for the nice housing. Kinda like those old dinosaur machines kept stock.
Couldn't you have put it into an MD-4003 chassis instead?

Well, when that nice Compass housing had a circuit board that was not fixable, what else you going to do with it? It didn't want to reside in the dark closet gathering more dust. Now it feels youthful again, ready to give those youngster detectors a butt whoop'in....LOL