MPP Beach REV-E

[Qiaozhi]

George, I just Finish cad drawing and getting ready to 3d print a 14inch mono coil in anticipation for the MMP gold, What induction do you suggest I make it I know the smaller induction the faster the decay, and the better for gold right ? also should I use the smallest magnetic wire I have and shield this coil ? speaking of shielding is copper tape with conductive glue a good idea for shielding ?

I wouldn't get too excited about the release of MPP Gold. At the moment it's just an idea that's still in the "getting ready to get ready" stage.

[MartyJ1963]

Hi all,,,Thanks again for all the help, I really appreciate it,,,,Before I decided to swap out the IC's I took both Detectors out into Farm lands near my home. There are not many houses on the street where I live and the street is totally surrounded on all sides with miles of Farm land. I took both Detectors out into the fields, miles away from any power lines, houses etc, and both detectors sound exactly the same as I tested them at home. I then swapped out all the IC's and there was no change. The IC's are from reputable companies. Apart from how it's sounding I'm really happy with the depth and sensitivity. @KT315,,,thanks for the information you quoted by Eric Foster. Would some one be able to tell me how to measure the frequency of the 555 that creates the main pulse please?,,,I have an oscilloscope but I'm not sure where to place the probes. I'm still learning,,and it's great to have help from such knowledgable people here on Geotech. Thanks again. Marty

[Tibuck19]

There are lots and lots of threads in the 'COIL' sub-forum about shielding and making Fast coils.
Do read and remember that shielding CAN increase the Capacitance and SLOW the coil's decay severely.

Yupe, that's why I going to make a 14 inch shielded in hopes I get a similar performance of a 12inch non shielded, Unless im not searching right, there doesn't seem to be much talk about using copper tape as shielding in the coil forums, that in itself can be a clue haha

[Tibuck19]

Hi all,,,Thanks again for all the help, I really appreciate it,,,,Before I decided to swap out the IC's I took both Detectors out into Farm lands near my home. There are not many houses on the street where I live and the street is totally surrounded on all sides with miles of Farm land. I took both Detectors out into the fields, miles away from any power lines, houses etc, and both detectors sound exactly the same as I tested them at home. I then swapped out all the IC's and there was no change. The IC's are from reputable companies. Apart from how it's sounding I'm really happy with the depth and sensitivity. @KT315,,,thanks for the information you quoted by Eric Foster. Would some one be able to tell me how to measure the frequency of the 555 that creates the main pulse please?,,,I have an oscilloscope but I'm not sure where to place the probes. I'm still learning,,and it's great to have help from such knowledgable people here on Geotech. Thanks again. Marty

I remember a while ago I also swapped the both ne555 for two different ones I had a bunch of them ( china made) perhaps the were not perfectly matched if that makes any sense.

[Tibuck19]

I wouldn't get too excited about the release of MPP Gold. At the moment it's just an idea that's still in the "getting ready to get ready" stage.

"Getting ready to get ready" sounds like procrastinating George, hahaha the 14inch coil was something on my mind for a while now.

[waltr]

Hi all,,,Thanks again for all the help, I really appreciate it,,,,Before I decided to swap out the IC's I took both Detectors out into Farm lands near my home. There are not many houses on the street where I live and the street is totally surrounded on all sides with miles of Farm land. I took both Detectors out into the fields, miles away from any power lines, houses etc, and both detectors sound exactly the same as I tested them at home. I then swapped out all the IC's and there was no change. The IC's are from reputable companies. Apart from how it's sounding I'm really happy with the depth and sensitivity. @KT315,,,thanks for the information you quoted by Eric Foster. Would some one be able to tell me how to measure the frequency of the 555 that creates the main pulse please?,,,I have an oscilloscope but I'm not sure where to place the probes. I'm still learning,,and it's great to have help from such knowledgable people here on Geotech. Thanks again. Marty

Good test which shows the second detector is beating with the AC Mains. I run into this issue building a HH and needed to do a fine adjustment on the Pulse rate.
The first 555 is the Pulse Rate for the TX and ALL following timing. Scope of TX's MOSFET drive will show the Frequency.
Do this with both detectors and I'm sure you will find that they are NOT running at the same frequency- this is NOT due to bad chips but simply the result the component tolerances. Remeber that the frequency of a 555 is set with Resistors and capacitors. So a slight trimming the the 555's freq setting R will tweak the frequency.

[MartyJ1963]

Thanks Waltr,,,,,Can't understand why the Rev E detector still gives a scratchy ticking sound out in the middle of nowhere,,it sounds exactly the same in my projects room,,no change???,,How do I test the frequency of the 555 that creates the 'Ticking' sound,,IE: Where do I place the oscilloscope probes? Grateful for the help Waltr. Thanks. Marty

[dbanner]

I think you might want to recheck your pcb for correct/incorrect parts placement etc. or for bad/defective component. The audio should be as smooth as silk.

[waltr]

and both detectors sound exactly the same as I tested them at home.

Sorry, I mis-read this as both detectors sound the same when out in the field.

Only thing I can suggest is use the scope and compare Stage by stage on each detector to find where the signals are different.

Did you use same quality/tolerance caps & resistors?

[Tibuck19]

Perhaps you could make either a video or an audio file of the MMP and how they sound, it could be useful for others and new to detectors in the future.

[MartyJ1963]

Thanks guys,,,,,When I first built the Rev D MPP I had a few mishaps because I had to resolder in a couple of places which caused some of the solder pads to lift - Silverdog (Andy) kindly offered to take a look for me and he repaired it for me,,,he did a great job with it and it works perfectly. I strictly took my time over 3-4 days building Rev E MPP and actually wrote every component down in my notes before soldering them in place,,,all resistors were 1% and every component was double checked with 2 different multimeters (In case of different readings) and then,as I've said, I logged it in my notebook before soldering. I have rechecked every stage also. Where do place the scope probe to check the 555 frequency? Apart from doing that next, I have swapped out all the IC's, several times, and there's no change, I know all the IC's are OK because I tried them in all my other builds that use those IC's and they're fine. I've ordered several more 220k Pots to try because sometimes as I'm turning the pot towards the point of a low growl, it begins to crackle and become high pitched and scratchy. Maybe a faulty Audio pot?,, Thanks again guys.

[MartyJ1963]

@Tibuck19,,,I don't have a decent enough camera at the moment to create a video,,,but I'll see what I can come up with in way of recording the audio of both detectors. I have a good camera on order-just waiting for it's arrival,,,Thanks. Marty

[Qiaozhi]

Marty ... I can assure you that the audio on the REV-D and REV-E versions should sound exactly the same. Your problem has nothing to do with anything beating with the mains frequency. In fact, your test in the field proves that.

Also, there's been some talk in the replies concerning the TX pulse rate, and whether you should use a higher pulse rate. This also has nothing to do with this particular problem.

Is it possible that you do not have the Threshold pot connected correctly? Without this pot connected, you would get exactly the results you describe. i.e. a high pitched audio tone with a scratchy note, but also some target detection.

[MartyJ1963]

Hiya Qiaozhi,,,,,I've finally solved the problem,,,and I feel so silly!,,At first, I thought it may be one of the IC's,,but after swapping them all out, numerous times, I found it was a faulty Audio pot all along!,,Both the Rev D and Rev E do now sound the same. Also,,and I'm honestly not exaggering, and I've tested it both in the Farm land and in my project room, I'm getting 14" on a 1 Euro and 12" on an English 5p piece,,,,is this good?(normal?),,,I'm really pleased with this detector and will be ordering another board soon for my partner Claire. The sound is really clear and sharp now. Could you tell me what the Threshold and Gain pots do and how to use them? Sorry for the foolish question but the depth tests I did were with the Gain and Threshold fully off. I want to thank you all so much for your knowledge and help and hopefully, when my new camera arrives (and I've learnt how to use it,,lol), I'll try and put some clips together before and after I seal it all up,,,can't wait to finish the shaft and enclosure now,,,I've carved some handles from some Yew wood that I cut and season myself that I use for making Longbows and hunting bows. Thanks again all. Marty

[6666]

it begins to crackle and become high pitched and scratchy. Maybe a faulty Audio pot?

A good clue.

Glad you fixed it, 14" on a 1 Euro is a good result.