Hi there!
This is a continuation of this year-old post:
http://www.diyaudio.com/forums/parts/252034-piezo-driving-solenoid.html
In a few words and simplifying the question:
I'm trying to trigger some hand-made solenoids by hitting a piezo disc (or rather, something that is glued on top of them).
Following the advice that I got on the earlier post (thanks for that!), I've done some signal processing on the output of the piezos:
piezo -> 9v preamp -> low pass filter at 20 hz* -> full-wave rectifier with a cap to turn the wibbly output of a piezo into a clean pulse.
So I hit the piezo, I get a pulse between 0.5 and 2.7 volts.
Now the only thing I need is some transistor to be proportionally switched by that pulse in order to drive a higher current through the solenoid (two or three 9v batteries).
Could you recommend me any?
Also, I've noticed two 9v batteries give a stronger kick wired in parallel instead of wired in series, which surprises me since I thought solenoids depended on voltage and not current.
Thank y'all!
* the low-pass is there to avoid vibration from the strings from getting into the piezo. See the old post if you're curious about that.
This is a continuation of this year-old post:
http://www.diyaudio.com/forums/parts/252034-piezo-driving-solenoid.html
In a few words and simplifying the question:
I'm trying to trigger some hand-made solenoids by hitting a piezo disc (or rather, something that is glued on top of them).
Following the advice that I got on the earlier post (thanks for that!), I've done some signal processing on the output of the piezos:
piezo -> 9v preamp -> low pass filter at 20 hz* -> full-wave rectifier with a cap to turn the wibbly output of a piezo into a clean pulse.
So I hit the piezo, I get a pulse between 0.5 and 2.7 volts.
Now the only thing I need is some transistor to be proportionally switched by that pulse in order to drive a higher current through the solenoid (two or three 9v batteries).
Could you recommend me any?
Also, I've noticed two 9v batteries give a stronger kick wired in parallel instead of wired in series, which surprises me since I thought solenoids depended on voltage and not current.
Thank y'all!
* the low-pass is there to avoid vibration from the strings from getting into the piezo. See the old post if you're curious about that.
If you turn the amplified pulse into DC, (half wave cap/diode) then amplify it again to match the solenoid requirements. That should do it.
Yes, that's the intention, but how? Are you suggesting a simple audio chip amp? I need a pretty strong current for the solenoid. How many watts, what chip?
Hi,
Reading the original post I'm at a loss as to what your trying to do.
Its way more complicated than you envisage if you want any
sort of proportionality and responsiveness to the system.
I'd concentrate on simply making your acoustic system louder.
Either by the design of the instrument or by amplification.
Forget about any electrical method of amplifying mechanical input.
Your fingers have plenty of power if used properly /effectively.
Look at how a piano works, noting the key point is the major part
of the hammers movement is due to pure inertia, so it will bounce
off the string and settle back, even if you keep the key depressed.
(Piano actions are a fascinating problem once you think about them.)
Note that a piano key is velocity sensitive. Tapping something
hard is more about pressure sensitivity and extremely difficult
to mechanically amplify, as energy coupling is very poor.
rgds, sreten.
Reading the original post I'm at a loss as to what your trying to do.
Its way more complicated than you envisage if you want any
sort of proportionality and responsiveness to the system.
I'd concentrate on simply making your acoustic system louder.
Either by the design of the instrument or by amplification.
Forget about any electrical method of amplifying mechanical input.
Your fingers have plenty of power if used properly /effectively.
Look at how a piano works, noting the key point is the major part
of the hammers movement is due to pure inertia, so it will bounce
off the string and settle back, even if you keep the key depressed.
(Piano actions are a fascinating problem once you think about them.)
Note that a piano key is velocity sensitive. Tapping something
hard is more about pressure sensitivity and extremely difficult
to mechanically amplify, as energy coupling is very poor.
rgds, sreten.
Work backwards.
Solenoid voltage requirement?
Power supply that will supply the required voltage, current will be supplied with the size of capacitor chosen.
Place the solenoid between the possitive and use a suitable switching transistor to negative.
The DC from your detector will switch the power transistor on and operate the solenoid. Employ a reverse biased diode across the solenoid to avoid damage to the switching transistor.
You may need a Darlington pair to work the level from your detector.
This is the general idea;
Piezo cell to op amp. out of op amp to DC circuit. DC circuit to Darlington and then to solenoid.
Hope that helps.
Solenoid voltage requirement?
Power supply that will supply the required voltage, current will be supplied with the size of capacitor chosen.
Place the solenoid between the possitive and use a suitable switching transistor to negative.
The DC from your detector will switch the power transistor on and operate the solenoid. Employ a reverse biased diode across the solenoid to avoid damage to the switching transistor.
You may need a Darlington pair to work the level from your detector.
This is the general idea;
Piezo cell to op amp. out of op amp to DC circuit. DC circuit to Darlington and then to solenoid.
Hope that helps.
Thanks again for taking the time to think and answer.
Sreten: it's true that pianos sound really loud using no more power than the finger's, however my building skills are limited and so are my tools.
I've thought of a system similar to a piano: when you push the fretboard down (there's an independent 1cm wide fretboard for each string), you're pushing down a piano key that, through the usual piano mechanism, will trigger the hammer. I'll do that someday, but I'm afraid it will take time to learn and design.
Also, meanwhile I'm building a prototype with simple pickup amplification.
JonSnell: the solenoids are hand made so they could be adapted to anything, but I was thinking of 18v. What would be the right transistor (or darlington pair) for a range of 0.3 - 2.7v at gate and 18v between drain and source? This is the main question.
Thanks!
Sreten: it's true that pianos sound really loud using no more power than the finger's, however my building skills are limited and so are my tools.
I've thought of a system similar to a piano: when you push the fretboard down (there's an independent 1cm wide fretboard for each string), you're pushing down a piano key that, through the usual piano mechanism, will trigger the hammer. I'll do that someday, but I'm afraid it will take time to learn and design.
Also, meanwhile I'm building a prototype with simple pickup amplification.
JonSnell: the solenoids are hand made so they could be adapted to anything, but I was thinking of 18v. What would be the right transistor (or darlington pair) for a range of 0.3 - 2.7v at gate and 18v between drain and source? This is the main question.
Thanks!
Ok, after much looking I found this two:
2n2222 - but this is npn, so current operated. This is a problem since the output of the piezo, even after the piezo buffer (I'm using this one: http://www.scotthelmke.com/Mint-box-buffer.html ) has a very tiny current. Adding a small 9v chip amp to the circuit seems too much power consumption.
2n7000 - according to some pages, this would be the mosfet equivalent of the 2n2222, so voltage operated. Vgs is in the range from 0.8 to 3v, so ideal.
I'll try and let you know!
2n2222 - but this is npn, so current operated. This is a problem since the output of the piezo, even after the piezo buffer (I'm using this one: http://www.scotthelmke.com/Mint-box-buffer.html ) has a very tiny current. Adding a small 9v chip amp to the circuit seems too much power consumption.
2n7000 - according to some pages, this would be the mosfet equivalent of the 2n2222, so voltage operated. Vgs is in the range from 0.8 to 3v, so ideal.
I'll try and let you know!
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