interfacing piezo sensor needs respective number of op-amps

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Anonymous
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 Intefacing Piezo sensor with PSoc4, I successfully tested a simple charge mode amplifier for it. 

   

My Problem is that my project maybe need to use number of sensors, maybe up to 16. 

   

If I keep use the charge mode amplifier, that means I need 16 op-amps, but PSoc4 provide just 2 op-amps, 

   

How can I resolve this problem. 

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Bob_Marlowe
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You could multiplex your input-signals to one OpAmp. this would take a reasonable time to stabilize, but you did not tell yet how much the frequency of the signals is. Wouldn't be too bad, when you tell us a bit more about what you want to perform.

   

 

   

Bob

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ETRO_SSN583
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If you mux a charge mode amp, since its corner frequency usually quite

   

low, there are very long settling times. Google "charge mode amplifier",

   

there are quite a few hits, TI, LTC, AD all have ap notes.

   

 

   

So take this into consideration.

   

 

   

Regards, Dana.

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Anonymous
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thanks all. 

   

If I mux multiple piezo sensors to single op-amp, I think I should wait the state of the charge amp discharged. 

   

Can I use a swich ( instead of feedback resistor ) to instantly discharge feedback capacitor to reduce discharge time ? 

   

Does PSoC provide the switch function? or Can I implement it with a discrete device outside of PSoC. 

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Bob_Marlowe
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You can program io-pins on the fly to be Hi-Z or connected to gnd, so this is like a switch as you need it. Beware of the restricted pin-routing capabilities of a PSoC4, so have all your IO's ready and working before you start to manufacure your pcb.

   

 

   

Bob

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ETRO_SSN583
Level 9
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Yes by using an open drain output to ground cap or

   

use an internal mux terminated in Vss. The former

   

approach has a much lower switch R than a mux.

   

 

   

So tradeoff is

   

 

   

open drain                                mux

   

lower Rdson                            higher Rdson

   

higher discharge spike         lower discharge spike

   

shorter discharge time          longer discharge time

   

 

   

Regards, Dana.

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Anonymous
Not applicable

 Hi!

   

I am trying to interface piezo sensors too.

   

Can you please shate with me the ampifier circuit? and the code? 

   

Did the "muxing" worked?

   

Thanks!!!

   

Anna

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ETRO_SSN583
Level 9
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If you google something like "single supply opamp microphone circuits" you get

   

quite a few hits.

   

 

   

One collection of circuits - www.circuitlab.com/browse/by-tag/microphone/

   

 

   

Regards, Dana.

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ETRO_SSN583
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Take a look at this thread for a discussion on mic interfacing -

   

 

   

www.cypress.com/

   

 

   

Regards, Dana.

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Anonymous
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Hi Piona.

   

Unfortunately, I stopped my project for interfacing multi-piezo sensors.

   

but if you have any question, I would like to be your help. 

   

thanks. 

   

kkadin. 

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Anonymous
Not applicable

Hi kkadin!

   

Thanks for your want to help:)

   

I am trying to interface piezo disk to psoc 3 . I built an amplifier that works great but when I am inputing a piezo it behaves strange. I am aware to the specs of the piezo and had learn ( a lot of google) that the best interface is charge amp with big resistanse load. I saw you made one:)

   

Just want to see 🙂

   

If you can please attache the schematics or tel me how you bias the "big resistance load"

   

Thanks!

   

Piona 

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ETRO_SSN583
Level 9
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Piona, on the other thread I did another config, using a Piezo, got ~ 1 V pk-pk

   

out if it.

   

 

   

   

 

   

   

 

   

Regards, Dana.

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Anonymous
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Hi Piona

   

 

   

unfortunately again, I cannot upload the files because my company is monitoring network..

   

but I think following information would be helpfull.

   

 

   

* for charge mode amp

   

Rf (Feedback R) : 10 MOhm

   

Cf (Feedback C) : 0.05 uF

   

opamp reference voltage : Vcc/2

   

vout = -Q/Cf + Vcc/2

   

Q : charge generated from sensor, I tested a pvdf film so your piezo disk needs another Cf 

   

Time constant : Rf*Cf, so you need to change Rf again

   

 

   

* reference link ( chapter 3.2 )

   

Signal Conditioning Piezoelectric Sensors from TI

   

http://www.ti.com/lit/an/sloa033a/sloa033a.pdf

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