Transistor power consumption

[Scarr]

Hi,

If I have a transistor to amplify a sensor voltage of 40mv per G(piezoelectric) will it consume power when stationary? if so what am I looking for on the tech sheets to give me this standby power consumption?

Thx

 

[Dean Huster]

Very few circuits DON'T consume power when "stationary". In order for the amplifier to linearly amplify the signal, it will have to be always biased so that it's consuming at least some current.

By why are you using a "transistor" to amplify this signal when you should be using something like an instrumentation amplifier, an integrated circuit made specifically for this application?

Dean

 

[Phasor]

Dean is right - a piezoelectric element has a very high output impedance, and hence, you need an amplifier with a very high input impedance, to measure the signal.

Op-amps are designed for this - I can't think of specific models offhand, which would suit, maybe someone else has a suggestion, or check manafacturers' sites.

 

[kinjalgp]

You can use FET input Op-amps like TLO82 / TLO84.
There are FET op-amps with very low noise but I don't have any idea about that.

 

[Scarr]

why is life never easy?

OK, so a simple transistor is not the answer, anyone help with a good simple solution? single IC with very low current consumption?

Thx

 

[Scarr]

Maybe I should just ask.....

I have had a thought, maybe I should just explain the problem and let people suggest solutions, maybe piezoelectric in not the answer.

So here I go.

I want to detect if a caravan/motorhome/vehicle is moving, I want to ensure wind or slight vibration does not cause a false alarm.

I want this event to trigger a relay, either directly (reliably) or via a PIC/AVR to allow some intelligence if required.

Thx

 

[Oznog]

TL082/84 may not be a good choice. Those are low noise, but not low offset. The offset error is going to be the problem.

You know you will only be able to sense acceleration, right? No accelerometer can sense speed. Your speedometer sensor should be used for this.

There is also a problem with thermal drift of the sensor's offset. Normal car accelerations are well under 0.1g, but the accelerometer's 0 g position can drift more than that. So you may need a highpass filter with a time constant lower than the max rate the sensor's temp can change but much higher than the rate of acceleration changes.

 

[Scarr]

Anyone seen a off the shelf motion detector

Thanks all for your help, if anyone reads this and knows of a very LOW power mechanism or device to use as a alarm movment sensor (does not need to be sensative just detect a car driving down a road) then please help.

Thanks.