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Hello Nigel,

 

Here is a quick listing of the stuff i got.

 

C1 – 0.1μF

C2 – 15pF 

C3 – 0.1μF

C4 – 22pF 

C5 – 0.1μF

C6 – 0.1μF

C7 – 0.1μF

 

 

R1 – 22k Ω    

R2 – 1M Ω     

R3 – 6.8k Ω   

R4 – 680k Ω  

R5 – 6.8k Ω   

R6 – 15k Ω    

R7 – 10k Ω    

 

Stripboard  ( 7 lines by 17 available holes nominal )

TL072 Dual Op Amp

8 Pin DIL Socket  

Battery Terminal   

Enclosure

Mic Piezo 27mm 20nF (or Korg contact etc.)

Grommets 

Shielded Wire

Jack sockets and plugs (if using, I am wiring direct which is why I have the grommets)

Shrink tube  as used by Stefan in his pic.

On/Off switch

 

If there is one tip I can give - The only thing that catches people out is that when you look at a stripboard the soldering is obviously done on the metal strips but the components are pushed in from the other side so for instance the TL072 pin "1" will be going through through the hole to the immediate right of R2  on the third strip down from the side without strips.  On Stefans diagram you must imagine you are looking through the stripboard and the metal strips are on the other side and the components are pushed through from the non stripped side that you are looking at.  If you don't get that right you will never get pin 1 on the op amp in the right place Once you get the amp in the right site then work out your gaps in the track then start putting on your components.

 

If anyone finds fault in what I have said please jump in - I will not mind.

 

Hope it helps,  Vic

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I just want to add to that, that when you're cutting the traces of the stripboard, you need to use the mirror image of what I've posted, since the cutting is done on the back side of the board, and what I show is the front side (as Vic has pointed out).

 

At some point I'll write up a full-blown construction article on my web site (or on watchoscope.com), but for now, the sketchy stuff will have to do.

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I think the resistors are the wrong values 0.6w.metal film...

 

and are the capacitors decoupling ceramic disc or resin dipped types?

 

sorry if i'm dragging knuckles here but i'm sure i can remember which end of the soldering iron to hold...

 

Nigel

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@svorkoetter " It'll be interesting to see what the sales potential is. I mean, how many watchmakers and WISes are there out there?"

 

at least from my point of view:

 

- all those watch enthusiasts who don't want to invest in a timing machine (not even a 200$ chinese one)

- all those that have already installed wildspectra and tickoprint on Android or Kelloo on Apple and that are frustrated they don't work as they should (but who will try to make a piezo amplifier and use it as a phone mic) and that they don't show amplitude

- all those that recently found out what a watch balance amplitude is and how it is calculated just from analyzing the tick-tack :)

 

Congrats on your work, great stuff!

Bogdan

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Hello Stefan,

 

Well the amp is put together and I can hear a watch ticking against the piezo but there is also some background noise.  I have used an aluminium box and have grounded to the box.  Should the shielding on the cables be grounded as well ?   I had to have the volumes turned right down on the Mic and speakers as initially there was terrific feedback, I had not thought to lower the volume on my PC speakers.  Can you advise the best way to test the quality / functionality of the amp.

 

Cheers,

 

Vic

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Hi Vic:

 

The shielding on the cables to both the microphone and computer should be attached to GND on the circuit, and the centre conductor attached to PZ IN for the microphone cable and OUT for the computer cable. If you have cables with two centre conductors, you can use just one. If the shielding is not grounded, then the cable isn't really shielded.

 

The best way to test is to use a set of headphones (e.g. from an old Walkman) or earbuds plugged into the headphone jack that most computer speakers have. That way, the piezo can't "hear" the speakers; only you can.

 

Stefan

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@svorkoetter "Yes, it ought to be, but I don't know by how much. I do have to manufacture the microphone stands, which has a materials and labour cost associated with it. What do you think the magical price barrier is? $99?"

 

Personally, I am interested only in the software. The rest I think I will manage to put it all together. I found a vid on youtube with an even simpler montage for the amp which I will try (

).

I think you should do more packets: sw, sw+amp, sw + amp+holder, with the main price value on the sw app. I still believe that your market is the amateur/hoby watchmakers, IMHO, who will find it quite rewarding to make the amp and the holder themselves.

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Personally, I am interested only in the software. The rest I think I will manage to put it all together. I found a vid on youtube with an even simpler montage for the amp which I will try (

).

I think you should do more packets: sw, sw+amp, sw + amp+holder, with the main price value on the sw app. I still believe that your market is the amateur/hoby watchmakers, IMHO, who will find it quite rewarding to make the amp and the holder themselves.

 

The problem with the amp in that video, and several other piezo pre-amps that I've found, is that they go out of there way to ensure that there is good bass response (which you do not get when connecting a piezo directly to a traditional amplifier). Unfortunately, that is exactly what we don't want for a watch timing microphone preamplifier. Most of the useful information lies between 300Hz and 1kHz. So, my pre-amp has both high-pass (~220Hz) and low-pass (~12kHz) filtering, which makes it great for watch timing, and lousy as a guitar pickup.

 

Regarding packaging, do you think there would be much of a market for the software with the amp but without the holder?

 

My current thinking is that the software, when installed, will have all features available for 60 days. After that most of the advanced features (e.g. long term tests) will be disabled unless you purchase. If you buy the software with the hardware, then of course, you get all the features without having to make an additional purchase.

 

So, if you're really cheap, you can build your own mic and amp, and use the limited version of the software forever (but it will remind you every time you start it that you can update to the "pro" version).

 

If you're a serious amateur or professional watchmaker but like building stuff, you can build your own hardware, make sure it's working with the free/evaluation version of software, and then pay for the "pro" version.

 

Or, if you want turnkey, you can just buy the whole bundle, which I think I can reasonably price above the cost of an entry level Chinese watch timer, since mine does far more.

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I will try to post the pics and stages in the making of the amp and will own up to the schoolboy errors I made on the way - some of which are really daft but I can take a ribbing.

May take a couple of days to sort out.

Cheers, Vic

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 Fair play Stefan, I think you will find my mistakes a bit more amusing and basic, for instance have you heard the one about the guy who put the heat shrink tubing on shrunk it to perfection and then peering throught the plastic noticed that there was no amp chip in the DIL socket - Doh

 

Cheers,

 

Vic

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Ok here we go. I get my scrap bit of Vero board and clean it up a bit finishing with a wipe with alcohol.

 

Then I study Stefans latest drawing indicating where the breaks are to be made.  If there was a lot I would use my Dremel with an etching bit but on this little one I just cut the breaks with a scalpel.

post-197-0-17644100-1415039434_thumb.jpg

 

Next I flip the board over and mark all the breaks on the no strip side this is easier for me to get my head around when putting on the components.

 

post-197-0-29482400-1415040869_thumb.jpg

 

I used a DIL socket rather than soldering the chip directly so I have placed that into position and soldered it in first.  This gives me a point of orientation for all the other components.

 

post-197-0-74861400-1415039589_thumb.jpg

 

As one of the smallest red bridges is under the DIL socket I decided to create a solder bridge.

 

post-197-0-70386800-1415039708_thumb.jpg

 

post-197-0-16807200-1415039776_thumb.jpg

 

And that’s the DIL socket in place.

 

post-197-0-52223900-1415039907_thumb.jpg

 

Now using the DIL socket as a starting point for working out the positioning of the components refer to Stefans diagram and start methodically soldering everything in place.  I started with the red wire bridges and then moved on to the resistors and finished with the capacitors.

 

post-197-0-49064600-1415040006_thumb.jpg

 

Continually check the tracks with a loupe to ensure there are no short circuits, a tiny bit of solder can bridge between tracks. I run the scalpel down each one and then test out with a meter just to be sure.

 

post-197-0-21773900-1415040162_thumb.jpg

 

So that’s the basic board together.  Next I drilled the enclosure – I used an aluminium one.

 

post-197-0-38486200-1415040240_thumb.jpg

 

I decided not to use Jack sockets on the box so there are two rubber grommets at one end and a switch at the other.  Through one I will lead a shielded cable for the Piezo and through the other the shielded cable for the Jack that goes to the computer Mic socket.  I will use the nut on the inside of the switch to get the ground to the box basically just tightening it on top of the earth wire.

 

So next we have the wires through the grommets and my shielded cable has a double core so I used the red wire as my central wire cut off the other wire and used the shielding as the ground.  This is done for the Jack plug wire and the Piezo wire. (The red wire in the pic hanging loose attaches to the switch pole and is the positive feed from the battery).  I have a last check on the wiring with my meter looking to make sure all is grounded ok and it is.

 

 

Time to shrink the wrapper with my wifes heat gun for her craft embossing.  Then to fit it all into the case.

 

post-197-0-04810100-1415040388_thumb.jpg

 

post-197-0-90254400-1415041525_thumb.jpg

 

On with the lid and that is that – now to test it.

 

post-197-0-60031300-1415040605_thumb.jpg

 

Things you should not do that I have done !!

 

Don’t cut the track breaks on the board in the wrong place

Don’t solder a capacitor or resistor in the wrong place.

It may not be necessary but I checked all capacitors and resistors with my meter before soldering them to the board.

Use shielded cable

Don’t use the two central cores in a shielded cable and forget to ground the shielding use only one core of the cable for your positive and the shielding for your earth.

Don’t forget to put the chip into the DIL socket before you put the heat shrink on – took me 10 minutes to work out why the amp was not working ! – Doh

Always check out all your circuit and tracks with a loupe to ensure there are no shorts.

Don’t short out the battery when fixing the on off switch – it gets quite hot !

If you use a metal enclosure remember to ground it.

 

In conclusion, my thanks to Stefan for patiently advising me during the construction and for allowing the use of his circuit diagram.

 

And it sounds like this

 

 

 

 

 

 

 

 

 

 

 

watch sound.mp3

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