TGSL Kit?

[ivconic]

Neat!

[dbanner]

Dooley's solution on his tdx3 is elegantly simple and nothing new. However, opto or varistor or whatever you want to call it, is not among what I would consider standard everyday easily available except for buying online. The others are too slow response. In old mouse there is seperate photo LED and transistor that can do the job. It is easy hack for free components
People seem to be a bit reflexive when it comes to minipulse plus. Somehow it falls to me to modify and improve design as I see fit. This I already have done to my satisfaction.
My criticism about the audio was supposed to inspire others to do same.
I state again, MPP is great project, and thanks again for bringing it to us.
Here is my minipulse build, modified Eric's original layout to include two stage preamp and better audio. I post layout as soon as testing complete.

[ivconic]

"TGSL KIT?" .... "MPP..." ?
Slightly off topic i'd say...

Whatever...
I was also annoyed by "tic tic" sound at various diy's i replicated through the years.
Than i saw Dooley's design and i made it. I like the solution. Pleasant sound.
Later on i randomly stumbled on decent batch of cheap yet pretty fine LCR 0202 analog linear optical couplings.
I was about to make precise adjustable 30-180Hz band pass filter.
So i bought several pieces from Aliexpress.
I used only one of those so far. Delighted with how fine it behaves actually.
Several others from a batch still keeping unused.
So i was thinking to make variation of Dooleys approach but with LCR0202.
Separate module, for to adding on any PI design.
In meantime i started to learn bit better programming. So now i want to control LCR with PWM from uPc.
Working around it in spare time.
Just to get the idea; here is the schematic of filter i made and the application of coupling:

[samsearcher]

Thats great Eric, I don't know what I need! can you help? I'm very much a beginner with detectors.
I have just received the MPP-beach kit Rev-E (looks like a great quality PCB) and a TGSL-EDU PCB only.
So I am looking for a 'fast coil' 10" to 11" apparently and something that's recommended for the TGSL?

john

[Ferric Toes]

Next I will need a couple of coil housings, are these available anywhere, or do I need to build a vacuum box and former?

What sizes are you looking for? I am in the process of having a stock-take due to an upcoming house move and have several sizes and configurations available in Dorset. What type of coil? mono, concentric, DD?

Eric.

[Qiaozhi]

There is a reason why the original Minipulse had a 'lousy' audio, in that it was developed as a land/beach version of the Aquapulse. The Aquapulse was originally designed as an easy to use detector for police diving teams in seaching for items such as knives and guns that had been thrown into ponds, lakes, or rivers. The divers wanted a sound that would stand out against the background noise of bubbles venting out of their breathing apparatus and the tick threshold was the preferred sound from a bone conductor phone held under the mask strap. The same applied to treasure divers when searching underwater wreck sites.

This reasoning obviously does not apply to land or beach searching and it is a pity that a change in the audio circuit was not made somewhere along the line. Lots of the original Minipulses were made and sold, and at the time the audio did not appear to be an issue, but we are talking of the 1970 - 1980's period.

Eric.

Thanks Eric. It's always good to know the philosophy behind the design decisions.

Why wasnt the audio done like this in the first place for the recent minipulse PLUS is a mystery.

As I've said before, there is no mystery concerning the audio of the MPP. The Minipulse had a 'lousy' audio (as you put it) because it was inherited from the original MP. Continuing the idea of knowing the philosophy behind the design decisions, here's how MPP was developed (quoted from the "Original Minipulse Project Details":

"Here's my 2014 present to the Geotech forum members ->

Over the Christmas period I managed to acquire a non-working Pulse Technology Minipulse PI Detector. The guy who was selling it said "I do not know the fault of this detector so just selling as spares or repairs".

The detector was in generally good condition for the age, but someone (who doesn't know what they're doing) had attempted a repair. Here's a list of the faults that I found:

The battery pack was missing.
A few PCB tracks were damaged.
Someone had tried to replace the MOSFET, but put the new one in back-to-front.
The series resistor between the MOSFET drain and the coil had been removed and not replaced.
The TX oscillator (555) was kaput.
There was a track short at the preamp output.
The audio (555) was also kaput, as was the transistor that varies the audio frequency.
All the trimmers had been tweaked.
And finally, the connector that goes to the headphone socket was in backwards. That had me confused for a while.

In the end I decided to back-engineer the PCB, and now I have a complete schematic drawn in EasyPC.

The coil is 543 uH (1R0) with a damping resistor of 310R.
TX is running at 80pps (unbelievably slow, but true) with a TX pulse width of 234us.
Main sample can be varied (REJECT pot) between 58us and 150us, although the coil will allow a minimum sampling time of 25us.
Secondary sample is at 204uS (max = 296us).
Both main and secondary sample widths are 40us.
There is no SAT, so it's a bit unstable. Depth is average for a coin, but is hopeless with low conductivity targets due to the 58us minimum sampling time.
The Reject knob is labelled as "min" (position 0), "foil" (position 4), "pull tabs" (position 7) and "max" position 8. However, foil is rejected even at position 0 (again due to the timing delays).

Note that PL5 is fitted, but unused (and is labelled "unknown").
There are a few locations near the bottom of the PCB where additional components have been left out during manufacture, and R46 and R47 do nothing except connect between BATT+ and -5V."

Silverdog and I both built REV-A PCBs for a modified version of the Minipulse, which was called Minipulse Plus (MPP). Once some of the initial errors were corrected, REV-B was released to the forum. The updates made were:

"1. The transmit (TX) pulse rate has been increased from 80pps to 1000pps, and the pulse width
reduced from 234us to 58us. This should make the detector more sensitive to small targets.

2. The original single stage (1000x gain) pre-amp has been upgraded to a 2-stage pre-amp, to
allow earlier sampling.

3. The discrete diode pump circuit has been replaced with an LT1054, and synchronized with
the transmitter. This modification was made to eliminate some unreliability problems with
the original circuit, and to reduce the possibility of switching noise from entering the power
rails. Also, the battery pack can now decrease from a nominal 12V to around 8.4V before the
+5V supply starts to drop out.

4. The PCB size has been reduced to 3.5" square.

5. There is now only one on-board trimmer. This is the setting for the minimum sample delay.

6. The battery check circuit has been eliminated due to potential difficulties in calibration for
users who do not possess an adjustable bench power supply.

7. There are separate connectors for TX and RX loops to allow the use of a balanced coil if
required.

8. The loudspeaker amplifier is now the default output, which simplifies the wiring for the
headphone socket.

All of the above changes were made after building the Rev-A version, and to differentiate the
Minipulse Plus from either the Surf-PI or the Baracuda, particularly the ability for earlier sampling."

The latest revision level is REV-E, and no-one has complained about the audio until now. That's 5 years since the initial project was started.
As you can readily see from the Completed Minipulse Plus Projects by Geotech members a number of members were very happy with the final result, and this represents only a handful of people who have built the MPP so far.

Since this is an open-source project, you are welcome to modify and improve the design as you desire. If some of these modifications become popular, then any future PCB revisions may incorporate these if deemed appropriate. Ground balance is one such modification that's under development, and I await your proposed audio mod with bated breath.

[dbanner]

For two tone for tgsl, look in the tesoro goldeen sabre thread, you will find pcb layout with full details, or look in tesoro thread for evolution of two tone development for tgsl. Use advanced search while in thread for key word "two tone"
For coil housing, check Don Bowers, he sells them, very affordable.

[samsearcher]

I do not know Norfolk, I buy components in local store (not well supplied) or aliexpress. But from aliexpress I test everything because there are lots of counterfeits.
I can provide entire kit, but not sure about postage

Thanks, a little misunderstanding..... components are not a problem........I only need coil housings (anyone in UK?) ....and a two-tone PCB.

john

[dbanner]

Thanks for that ,Eric.
Eric, I was specifically talking about the minipulse PLUS, not your original minipulse, which I can fully understand the logic behind its development and evolution, beyond your Aquapulse non-bone cruncher audio.
I've already used the 555 via an FET for audio chopper just like in the CS6PI. Still needed to use the old nuggle to alter some tracks, cutting, jumping litlle wire here and there, which I dont like doing.
Why wasnt the audio done like this in the first place for the recent minipulse PLUS is a mystery.

[Ferric Toes]

The MMP is great project, very nice indeed, except for lousy audio. Yes, one can experiment with different types of audio circuits to improve the overall sound. there are many circuits already posted on forum to do just that. unfortunately it requires major alteration/mods to PCB, including designing of small Add-on board to go alongside original board with bunch of wires going back and forth. Not something the average do-it-yourselfer may relish attempting. I'm sure many hundreds of hours of effort went into MPP project, including design of very nice PCB. Its a shame that a little more effort wasn't made to give it a better sounding audio( something along the lines of the TDI)
I'm certain if this was the case, several hundred more kits, perhaps even several thousand would have been sold over the lifetime of the project. Some people don't wish to be tinkering around with extra circuitry, they just want to build the thing and go hunting.
Cheers.

There is a reason why the original Minipulse had a 'lousy' audio, in that it was developed as a land/beach version of the Aquapulse. The Aquapulse was originally designed as an easy to use detector for police diving teams in seaching for items such as knives and guns that had been thrown into ponds, lakes, or rivers. The divers wanted a sound that would stand out against the background noise of bubbles venting out of their breathing apparatus and the tick threshold was the preferred sound from a bone conductor phone held under the mask strap. The same applied to treasure divers when searching underwater wreck sites.

This reasoning obviously does not apply to land or beach searching and it is a pity that a change in the audio circuit was not made somewhere along the line. Lots of the original Minipulses were made and sold, and at the time the audio did not appear to be an issue, but we are talking of the 1970 - 1980's period.

There is the possibility of a simple modification that keeps the existing 555 timer but runs it at a fixed frequency, say 500Hz, and drives a chopper transistor that simply chops the d.c level from the final amplifier stage. This should drive phones via a simple filter to tame the edges.

Eric.

[Hyena]

I do not know Norfolk, I buy components in local store (not well supplied) or aliexpress. But from aliexpress I test everything because there are lots of counterfeits.
I can provide entire kit, but not sure about postage

[waltr]

Thanks, I did ask..... but no. Still looking for a two-tone PCB....anyone?

Next I will need a couple of coil housings, are these available anywhere, or do I need to build a vacuum box and former?

have bought coil form here:
https://sites.google.com/site/dbcoilshells/home

I did two tone with a PIC for HH. Detail in my thread here:
https://www.geotech1.com/forums/show...ake-on-the-HH2
Posts #25 & #97

I

[samsearcher]

Order from where? Recommended Hayes Electronics is not there anymore?

[Hyena]

Thanks, I did ask..... but no. Still looking for a two-tone PCB....anyone?

Next I will need a couple of coil housings, are these available anywhere, or do I need to build a vacuum box and former?

Make IGSL, its two tone. PCB you can etch by yourself. There are common components which you can buy in local store. Effort for building former and patterns is acceptable only if you already know that you will make many coils. If you want only one, order it.

[samsearcher]

you could also try asking silverdog, he may put you a kit together, he does it as a side line to his "proper" job which is why he only does full kits for certain md's, but he is not an ogre, ask him he may hook you up if he has the means.
aly.

Thanks, I did ask..... but no. Still looking for a two-tone PCB....anyone?

Next I will need a couple of coil housings, are these available anywhere, or do I need to build a vacuum box and former?