Piezo speaker, electronics help required

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jarrett
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Piezo speaker, electronics help required

Post by jarrett » Wed Jan 02, 2019 5:31 pm

Looking for advice re piezo speaker/sounder that i wish to use to make a set of headphones for the Vallon, i know the detector uses piezo earpieces and have got a couple from the auction site but have realised that you get active(with the circuit built in) and also passive which is what i have got and without the circuit.
I have made a lead up and tried them and they work but am concerned as on the sales blurb it stated they work on AC which i thought odd and so i need to find out what the o/p is from the detector be it ac or dc,i do not have a scope but have a dvm and an old AVO so could i switch between ac/dc and the one i get a reading on will that be the output?
Will also be looking for advice as to wire in series or parallel although i think it it different with piezo as i cannot get a resistance reading so must be high, will post some pictures when it is all finished with the method.



Fusion
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Re: Piezo speaker, electronics help required

Post by Fusion » Wed Jan 02, 2019 6:16 pm

I would say you'll be wanting to wire the earpieces in parallel.
Re: working out what is the audio output from the machine, it's easier if you actually use an audio transducer, such as existing headphones, or your Vallon ones. I would recommend using a series resistor, say 100 Ohms, so if you do stick them on a DC voltage, the thump won't harm them or your eardrums.
Are you aware of the long Vallon thread on the Geotech1 forum? There's almost certainly the answer to your question somewhere in that thread.
:(

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Re: Piezo speaker, electronics help required

Post by jarrett » Wed Jan 02, 2019 10:39 pm

Fusion,
Yes have seen the Geotech thread, but the Vallon uses a single earpiece which is a piezo one as issued and i do not want to pay a fortune for say Grey Ghost headphones which as far as i am aware use a crystal earpieces, i could buy a couple of Vallon earpieces for about 30-35 quid but it would be sacriledge to start chopping them up for what i want to make and do not fancy using ordinary speakers as then you are messing about with a matching transformer.
Have just re read your post ref audio transducer and that is what i have.

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Re: Piezo speaker, electronics help required/Vallon

Post by jarrett » Thu Jan 17, 2019 6:39 pm

Day off today so fired the shed woodburner up and made a start on the headphones, well converted ear defenders with piezo sounders fitted, the covers just snap off and then the foam was removed and put to one side also the foam that goes on the inside of the headband was removed as this is where the cable will run from one earpiece to the other in a convenient channel, the white plastic hard foam type of stuff was used as backing for the sounder which was cut around and then hollowed out for it to sit in with the foam that was already fitted will go back on top,bear in mind that these sounders should ideally be firmly mounted to get the best sound level so it is a bit hit and miss untill powered up but they are held firmly by the foam but if a failure will have to revisit it,anyway it's picture time and will post more tommorow.
stereo 001.jpg
stereo 003.jpg
stereo 004.jpg
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Last edited by jarrett on Thu Jan 17, 2019 11:17 pm, edited 1 time in total.

Beachcomber
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Re: Piezo speaker, electronics help required

Post by Beachcomber » Thu Jan 17, 2019 7:31 pm

Piezo's generally are AC driven, try to avoid any DC on them.
You can block the DC by fitting a 1 uF capacitor in series, if in doubt.

If you just wire them in parrallel with the existing Piezo (I assume) then you should be ok.
If they are not loud enough, mount them screwed on to a plate of solid material with two small screws.
If they are still not loud enough you would have to use a driver chip like a MAX4410.
Need the info. on the piezo units to know more.
This may help.
https://forums.adafruit.com/viewtopic.php?t=22444

Good luck mate
98;

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sweepstick47
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Re: Piezo speaker, electronics help required

Post by sweepstick47 » Thu Jan 17, 2019 10:38 pm

An interesting post and project by jarrett with some equally helpful replies resulting. Looks like the h/phones will be a proper job once completed. Looking forward to seeing the end result ::g
Regards ss47
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Re: Piezo speaker, electronics help required

Post by jarrett » Thu Jan 17, 2019 11:02 pm

Mr B, I could not find anyone with a 'scope to test the output from the md but for what the piezo's cost i got them anyway and tried a jury rigged test with the md and it worked which led to this project, they are Toko PB-1720, 30mm Passive Piezo and the seller did state they will only work with ac.
Regarding the cap would a electrolytic be ok for the job or should i try it without first.

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Re: Piezo speaker, electronics help required

Post by Beachcomber » Thu Jan 17, 2019 11:21 pm

I would fit a capacitor if in doubt.
You have an AVO- if there is no constant DC level showing, you should be ok.
Electrolytics will be fine if they are positive towards the equipment and neg toward the piezo. You can tell by measuring which side is more positive.
A scope is such a lovely piece of kit when you really need one!
AVO's are cool, I have an old 8, lovely meters 98;

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Re: Piezo speaker, electronics help required

Post by jarrett » Thu Jan 17, 2019 11:53 pm

Funny that as i have an old avo in a wooden box and prefer it over a dvm for the simple reason you get a nice steady reading depending on what is being measured trouble is the box weighs a ton with the high voltage resistances in it and i already have a hernia!

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Re: Piezo speaker, electronics help required

Post by jarrett » Fri Jan 18, 2019 2:12 pm

Ok time for more pictures, the first shows the backing foam with a piezo in it and the second is it in the shell, the wire will be routed from top of phones into the shell, the last picture shows the link wire for the other side which is a piece of stereo cable from probably something like walkman headphones, the screen and two of the wires are not used so were chopped off, this lead was used as i had it in a odds and sods box but the main reason being it is a nice fit in the headband.
More pics tommorow although it's a pain waiting for the clock so you can post.
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Re: Piezo speaker, electronics help required

Post by sweepstick47 » Fri Jan 18, 2019 2:34 pm

It's coming on and looking good ::g Is that a plywood sheet protecting a workshop bench by any chance? Regards ss47
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Re: Piezo speaker, electronics help required

Post by jarrett » Fri Jan 18, 2019 7:22 pm

Thank you, yes ply over chipboard so when it gets worn remove and just slap another piece on top ;)

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Re: Piezo speaker, electronics help required

Post by jarrett » Sat Jan 19, 2019 12:01 pm

More pics this time showing how it looks fitted in the shell before the original foam and cover is snapped back on, before the other side is done i will hook it up to the md to see what the audio level is like in case they need mounting more firmly to the shell for a higher sound level although the Vallon does have a volume control.
Next pic is the link wire showing the grooves in the headband, this will be hidden once the original foam is refitted.
This is the feed wire from the md,it has 4 wires but 2 will be chopped off and the 2 pieces of black cord are for strain relief, not sure what to do hear as the lead is quite a snug fit in the rubber insert that stops the cable from bending so may put a cable tie around the lead and see how it goes,i have used a military lead from a headset so good quality although years old and prefer it over the curly leads as they always seem to be getting caught in branches etc plus the Vallon has a normal lead as issued.
Right off down the hovel to fire up the soldering iron and see what the volume level is like, enjoy.
stereo 011.jpg
stereo 012.jpg
stereo 013.jpg
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Re: Piezo speaker, electronics help required

Post by jarrett » Sun Jan 20, 2019 5:14 pm

Did not get much done due to family over for the night but did measure voltage output which seems a bit odd as am getting 10vdc and 13vac but the ac drops a tad when it bleeps, have ordered some 1uF capacitors so cannot do much at the moment but will report when caps fitted and have a reply and advice from Beachcomber.

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Re: Piezo speaker, electronics help required

Post by jarrett » Thu Jan 31, 2019 3:50 pm

ight here we are again with more pics but first can i thank Beachcomber for his help on the piezo's, the idea for this was bought about by the fact the single issued earphone/earpiece would not cut the mustard regarding noise, well it would but the other ear with nothing on it would not.
After searching various forums and links where others have done the same it was the route i chose so none of this is my idea as it has been done before and i am posting here in case others want to give it a try, total cost is of the order of £2.20 ish for the piezo's every thing else i had at hand although the plug for the tector is about £18 if you buy it, the lead entering the headphone, only 2 wire but the other pieces are strain relief cords but not used as the lead is a tight fit in the flexi grommet.
stereo 013.jpg
Vallon 001.jpg
Vallon 003.jpg
Showing the lead soldered up with link to other earpiece and the finished job, probably a couple of hours work in all, once again thank you to all who helped and advised with this and lets see what other Vallon owner on here will be next to try the mod, normall speaker h'phones can be used but require a small transformer which you maybe just fit in a headset.
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