Hello

My friend and I are trying to make an electric circuit that will output high voltage when really small vibrations occur. We use minisense100 (a piezoelecteic sensor) to mesure the vibrations.
We tried many schematics and still failed to recive those results. We have 5V supply voltage and we are using LM741.
We think maybe the LM741 can't handle such low voltage.
Is anyone familiar with a schema that we can use or maybe what kind of op-amp will be good for this case?

The sensor's datasheet:
https://www.sparkfun.com/datasheets/Sensors/Flex/MiniSense_100.pdf

Thanks!

 

We think maybe the LM741 can't handle such low voltage.

Bingo. If you read the data sheet, you'll find that the 741 cannot get near either power rail for its input sensing or for the output. I forget the numbers, but basically your operating voltage range is very narrow or non-existent on a 5V supply.

You could use a 741 (or any op-amp) if you give it enough range to open up a gap – an operating range – in between the rails. Then you need to bias the input signal into the center of that range, so that you can pick up AC variations in the input voltage and amplify those up to the output range of the op-amp.

If you choose an op-amp that can sense down to the negative rail (LM358 is an old one widely used for this), then you could bias the input at ground and just amplify the positive parts of the input waveform. That's probably the easiest approach.

You don't really need a rail-to-rail op-amp or this application, but they are out there. I'm using the TLV271. It would work on 5V and would give you that full range.

 

You may want to give this a read:Signal Conditioning Piezoelectric Sensors and take note of how the TLV2771 is used as a charge amplifier on page 4. This gets you what you want and you can see how using a single supply of +5 Volts works out. Note how the non-inverting input is biased at 1/2 Vcc. I agree with wayneh as to the old LM741 being a poor choice for your application.

Ron

 

Bingo. If you read the data sheet, you'll find that the 741 cannot get near either power rail for its input sensing or for the output. I forget the numbers, but basically your operating voltage range is very narrow or non-existent on a 5V supply.

You could use a 741 (or any op-amp) if you give it enough range to open up a gap – an operating range – in between the rails. Then you need to bias the input signal into the center of that range, so that you can pick up AC variations in the input voltage and amplify those up to the output range of the op-amp.

If you choose an op-amp that can sense down to the negative rail (LM358 is an old one widely used for this), then you could bias the input at ground and just amplify the positive parts of the input waveform. That's probably the easiest approach.

You don't really need a rail-to-rail op-amp or this application, but they are out there. I'm using the TLV271. It would work on 5V and would give you that full range.

Thank you very much!
We will try the TLV271. Do you have a schema we can use with it?

 

My friend and I are trying to make an electric circuit that will output high voltage when really small vibrations occur.

Hi.

What is the purpose of this device?

 

There are schematics in the links I provided and suggested you read.

Ron

 

Hey,
We used tlv2771 and it was working but when we chabge to tlv2770 it's not.
There are differences between the two?

 

Hey,
We used tlv2771 and it was working but when we chabge to tlv2770 it's not.
There are differences between the two?

Yes, read the data sheets and check the pin outs. Offhand I am not sure of the differences. However, the data sheet should point out where your problem may be.

Ron

 

Yes, read the data sheets and check the pin outs. Offhand I am not sure of the differences. However, the data sheet should point out where your problem may be.

Ron

We have read the datasheet and used the right pinouts, yet it seems to work differently and we cant spot why.

 

Can you post your schematics as I really don't have an answer and maybe someone el;se will but drawings would be needed to compare along with detailed descriptions.

Ron

 

Pin 8 is functional on the 2771 but should not be connected on the 2770.

 

Can you post your schematics as I really don't have an answer and maybe someone el;se will but drawings would be needed to compare along with detailed descriptions.

Ron

We are using the schematic you send us.

 

We are using the schematic you send us.

Yes, using the 2771 example and the 2771 version worked. Did you note Alec's comment as to pin 8? Using a 2770 pin 8 should not be used.

Ron

 

Yes, using the 2771 example and the 2771 version worked. Did you note Alec's comment as to pin 8? Using a 2770 pin 8 should not be used.

Ron

Do you mean the Shutdown function?
If you do, we dont use it.

 

Other than pin 8 (Shutdown) the pinouts should be the same assuming TLV2770 D, DGK† OR P PACKAGE and TLV2771 D PACKAGE. I have no clue why one works and one doesn't.

Ron

 

Other than pin 8 (Shutdown) the pinouts should be the same assuming TLV2770 D, DGK† OR P PACKAGE and TLV2771 D PACKAGE. I have no clue why one works and one doesn't.

Ron

Thank you very much for trying help us!