Vallon VMH3CS Mine Detector

[jaypay]

It should work well ,I noticed that there was I think 15v on one of the pins of the headphone socket ,maybe you could power it from that ? on the subject of the socket has any one seen any rs232 data on any of the pins ,It would be interesting to know how it is enabled ,I guess that the terminal would have to send the correct characters to start the data flow ,it would be nice if the data contained information on the type of metal detected as well as the strength of signal (it would be nice but not likely I know).

[Ferric Toes]

Yes, that was my next move as the Bluetooth phone I have also incorporates FM radio. You can get very small FM transmitters that plug into an iPhone that may be suitable.

[jaypay]

some bluetooth headphones have a FM radio built in, maybe you could use a fm transmitter / modulator to transmit the audio ,some times analogue is best. I allso use a small transformer on my vallon to alter the audio impedance from high to low

[ivconic]

NRF24L01 is very good solution for that. After the setting active RX/TX mode (120-130uS) packets are transmitted somewhat bellow 1mS.
Quite good for wireless headphones and similar applications.
But it's just plain data TX/RX. You'll have to figure out how to make raw audio from that.
Maybe simple adc/dac with just two states and some simple vco on RX side is enough.
Actually this is pretty real solution for PI detectors.
Otherwise... those cheap Chinese wifi headphones are having unacceptable latency time for this purpose.
There are also cheap 433Mz RF modules, but than you'll not have "pairing" feature and you can't use more than one of such sets on the same field.

[kingswood]

Excellent thanks Eric

[Qiaozhi]

Does anyone
know why this happens?

This is a known problem with Bluetooth, and is referred to as "latency". How bad it is depends on the particular hardware and software. Apparently, Bluetooth 4.0 has the lowest latency. The delay with Bluetooth can be as long as 200ms, and in applications like metal detectors this is quite noticeable. Newer versions can get down to 100ms, and Bluetooth Smart Technology is claimed to be 6ms.

[Ferric Toes]

Hi Eric. Sorry for quoting such an early post
So I chopped the earpiece end off one of the phones I have today....I have a brown wire, white wire and silver wire.....How do i go about connecting that to a set of "normal" headphones??! Help !

This is a quick solution rather than an elegant one if you want to run standard low impedance phones. The phones shown in the picture are quite cheap, and when switched to stereo they are in series with the ground as common. If you disregard the ground then the series dc resistance is 60 ohms (30R per insert).

What you need then is an LT-44 transformer, available on ebay and connect up as shown in the photo. It is important that the secondary side connects to the tip of the jack plug and the second band only. The third band on the plug (nearest the body) is not used. The phones are readily available (ebay again).

I am planning to use an in-line jack socket, rather than a panel mount, and put the whole thing in a small plastic housing. This arrangement gives adequate volume and which can be turned down with the controls on the phones.

The silver wire you referred to is an outer braid on the twin cable which goes to ground in the detector. This can be cut off where the white and brown wires poke out, as a ground is not needed in this arrangement. Note that the nearest connection on the transformer is not used.

I am working on a wireless headphone setup and tried a Bluetooth transmitter which gave good audio on bluetooth phones, but there is a delay which is unacceptable. The coil has gone past the target by 10-15cm when the signal peaks. Does anyone
know why this happens?

[TH'r]

Vallon

Hello Eric; My Vallon #1 had a sticker on top, like the attached photo, when I received it. It was considerably defaced, and since I did not attach any significance to it till I saw this picture yesterday, I scraped the remains off. This one may have the "sub- munitions" up grade which could account for its much increased sensitivity to the 1 X 1 Std. Wgt. foil over my newer Vallon.

[kingswood]

The pinout is a bit puzzling as you would think pin B is the live audio connection. However, it appears that pin D is the one to choose (marked Tone). To mute the internal piezo speaker you link B to F, which can be checked with a test meter on the connector on the phone supplied with the detector. Some suppliers do not include a phone which is a one-ear job and doesn't look the part.
So far I have only tried piezo headphones such as Gray Ghost waterproof and Whites Surfmaster phones. The Gray Ghost are fine as they are, but Whites were much too loud and I had to make an in-line attenuator. The audio Volume can of course be adjusted on the detector by switching to the speaker symbol on the control knob and the pressing the + or - buttons to increase or reduce the volume. This is fine except that when the detector is switched off, the new setting is not stored. A sensible precaution for mine detection when you want every detector to have a default setting on switching back on, but a nuisance for hobby use. I have not tried low impedance phones, but I would be surprised if they worked without a matching transformer. Piezo phones do not appear to be readily available except for the high priced models so far tried.

Eric.

Hi Eric. Sorry for quoting such an early post
So I chopped the earpiece end off one of the phones I have today....I have a brown wire, white wire and silver wire.....How do i go about connecting that to a set of "normal" headphones??! Help !

[kingswood]

Have since done a bit more reading....8 inches on 1.8g buried is pretty good!
I will experiment next weekend with it buried deeper.

[kingswood]

Sorry no phone today so didnt get a video.
I took a 1.8g round'ish nugget with me in a plastic sleeve. Dropped it into a hole about 8 inches deep...Vallon detected it with ease
Will try deeper next time.
Walked up an old creek bed and had a couple of false alarms....Dug right down and I think it was white clay.

[kingswood]

EXCELLENT thank you much appreciated

Hope that helped. Sorry it wasnt the best example as the ground hadnt chnaged much. Will do one tomorrow with different ground and it may show the noise reducing better

[6666]

Probably not the best example of the Vallon GB as the area was pretty similar to the area I had just covered!....Will try and get a better video tomorrow.
Great 2 hours out this morning....no gold, but man this thing can hit small iron targets!! Half a metal staple, no worries !
https://www.youtube.com/watch?v=fT2V...&feature=share

EXCELLENT thank you much appreciated

[kingswood]

Probably not the best example of the Vallon GB as the area was pretty similar to the area I had just covered!....Will try and get a better video tomorrow.
Great 2 hours out this morning....no gold, but man this thing can hit small iron targets!! Half a metal staple, no worries !

https://www.youtube.com/watch?v=fT2V35na4jo&feature=share

[Ferric Toes]

Success! To remove the black threaded part I used a rubber strap wrench with a band cut from a palm pad for taking jar lids off, for added grip. A hook scribe worked well to remove the O rings, being careful of its point so as not to damage them. The rear threaded ring was frozen to the front part, as I was concerned about damage in separation, I left them stuck together. On reassembly I screwed the whole assembly to the correct position, then sighted thru the set screw hole for groove location to position the battery tube support. Many thanks for the information. If you make a booklet of information I would like the particulars on how to obtain one.

I'm pleased to hear that it worked. The back ring must have been over tightened against the end of the thread on the battery tube. It should come free with a bit of WD40 and some extra force. I don't think dust would have got in there, or that it is corroded as both surfaces are anodised. I am preparing a complete dismantling procedure as I have already a couple of requests for this. When this information is ready, I will let you know.

Eric.