Vallon VMH3CS Mine Detector

[daverave]

What is your sample pulse delay time?

my sample delay is about 13 uS

[6666]

Yes, there are a few problems I have come across though. The multiturn trimmer for adjusting the output voltage has quite a bit of backlash, so turning it one way, and then back, the action is not immediate.

Mine will not run on one of my bench power supplies, but the other (older) one it is OK. Batteries work OK

Small box shielded with copper tape seems effective in stopping radiated noise but I had a bit of a problem with conducted noise. Some good quality capacitors on input and output leads fixed that, together with a linear regulator and low esr electrolytic cap on the final output.

What I am doing here is taking the three series Li-ion batteries and setting the converter output to 15V. This I then regulate to 12V for the TX circuit. I need to do this so that the TX voltage remains constant over the range of battery voltage otherwise the calibration of my viscosity meter will not hold.

Eric.

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Hi Eric
thanks for taking the time to tell me this info, will test them out asap.

[Skippy]

On the subject of boost regulator modules, it should be easy to replace the cheapo trimmer pot with a fixed resistor of suitabe value to get the output you require. The circuit will be a basic potential divider network feeding back to the regulator IC, often 1.25V, or more common now is 0.6V, look for the IC datasheet.

I have just bought one of these regulator modules which is similar:
http://www.icstation.com/sx1308-conv...er-p-6016.html
It was just 2 GB Pounds delivered, from a UK-based eBay seller. It has impressive output power for its size. I am using it for a high-power LED torch/flashlight project for bicycle use. Two 18650 Li cells, the DCDC board, and 5 x 1 Watt LED module make for a decent light. I will post up a thread in the general electronics section soon, just for interest.

[daverave]

i used a buck voltage converter in one of my metal detectors and it works very well.

[Ferric Toes]

Previous excerpts:

I think I have too! Plus I think I have found the use for 2 of the 4 MOSFETS... like maybe disconnecting virtual ground from the coil and kickstart capacitor during flyback, breaking the damping R path and providing voltage doubling charge to the kickstart capacitor while it is de-referenced from virtual ground... Plus, I think I am missing about 3 ohms (remember 6 Volts at 1 amp) in the TX coil to virtual ground (probably in the flyback ground de-referencing MOSFETS)... I need to do some modeling!!! Any chance you can read the P/N of the MOSFETS?

Mosfets are 4 x IRF320 with 4 more on underside in almost the same position. I can't see the P/N so they may be a complementary type. There is only about 1/4 space between the two boards which I cannot part without breaking a lot of connections.

Eric.

[daverave]

Hi Eric...Tried several times to send you a message to your inbox but message came up saying your mail box full and need to delete some mail before i can send to you.

[Ferric Toes]

Hi Eric...Tried several times to send you a message to your inbox but message came up saying your mail box full and need to delete some mail before i can send to you.

Hi Dave,
I have deleted some messages, so try again.

Eric.

[Ferric Toes]

I have made some ergonomic improvements to the VMH3CS in the form of a proprietory armcup and a clip-on ground stand. The original 'rabbit eared' armcup base was retained, but with a small amount of machining, to fit the new stronger and better looking one. A 8mm nylon bolt was also fitted to lock it into place and stop the tendancy to slide up or down the battery tube, as it did previously.

Another useful bit of information is that I think I have identified the preamp chip in the electronics. It is a TI OPA627AU which described is a very low noise precision high speed Difet opamp. I look forward to getting a scope on the output sometime soon. Being a SOIC on a crowded board, that might be a bit tricky.

Eric.

[tifred]

Hello Eric

It is a very nice work!

Fred

[daverave]

I have made some ergonomic improvements to the VMH3CS in the form of a proprietory armcup and a clip-on ground stand. The original 'rabbit eared' armcup base was retained, but with a small amount of machining, to fit the new stronger and better looking one. A 8mm nylon bolt was also fitted to lock it into place and stop the tendancy to slide up or down the battery tube, as it did previously.

Another useful bit of information is that I think I have identified the preamp chip in the electronics. It is a TI OPA627AU which described is a very low noise precision high speed Difet opamp. I look forward to getting a scope on the output sometime soon. Being a SOIC on a crowded board, that might be a bit tricky.

Eric.

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very nice improvements to the vallon

[Qiaozhi]

I have made some ergonomic improvements to the VMH3CS in the form of a proprietory armcup and a clip-on ground stand. The original 'rabbit eared' armcup base was retained, but with a small amount of machining, to fit the new stronger and better looking one. A 8mm nylon bolt was also fitted to lock it into place and stop the tendancy to slide up or down the battery tube, as it did previously.

Another useful bit of information is that I think I have identified the preamp chip in the electronics. It is a TI OPA627AU which described is a very low noise precision high speed Difet opamp. I look forward to getting a scope on the output sometime soon. Being a SOIC on a crowded board, that might be a bit tricky.

Eric.

There are currently 6 Vallon VMH3CS detectors on UK eBay at the moment. This one has a broken arm cup, and the lowest price ->
http://www.ebay.co.uk/itm/1320091456...%3AMEBIDX%3AIT

[Mechanic]

There are currently 6 Vallon VMH3CS detectors on UK eBay at the moment. This one has a broken arm cup, and the lowest price ->
http://www.ebay.co.uk/itm/1320091456...%3AMEBIDX%3AIT

Damn it, they don't ship to Aus
I think one of these would make a cool play toy!

[ivconic]

Little off topic but i think is good to be mentioned here.
Just as Eric mentioned OPA627; i searched the Internet and coincidently i stumbled on this:
http://zeptobars.com/en/read/OPA627-...ake-china-ebay

"...Being a SOIC on a crowded board, that might be a bit tricky..."

Think twice!

"...Manufacturer (Texas Instruments / Burr Brown) sells them 16-80$ each (depending on package & options) while on ebay it's cost was 2.7$, shipping included..."

"...It does not seems they earned alot of money here - it's more of an economic sabotage..."

[kt315]

Plastic one was dissolved in acid

while some geotechers do not able delete chinese snot in the coils LOL! good pro autopsy

Good thing that they did not used something like LM358

have to read BB sign on the chip first!

[ivconic]

https://en.wikipedia.org/wiki/Dichloromethane