Accelerometer circuit design

Thread Starter

dimV

Joined Jun 20, 2020
3
Hello people ,
I dont know if my question is under the correct category but anyway

I need to design a very basic accelerometer circuit . The point is to take the voltage measuerement that a capacitive accelerometer provides and after proccessing it to output it .
The circuit will probably only consist of a few capacitors and resistors , an A/D converter ,an amp and integrators.
I have searched a lot online and have found very few info about such a topic , most are about the construction of the accelerometer. I have a some knowledge about op-amps(integrator,differentiator) and signals.
So if anyone can explain how and why things happen i would be very happy.

P.S i am talking about a diagram not any actual sensors , its more about understanding the concept
 

KeithWalker

Joined Jul 10, 2017
1,055
Which accelerometer are you planning on using? There are different frequency ranges and sensitivities. Some have a built in fet amplifier and some are just a capacitive element or a ceramic transducer. The circuitry will be different for the different types.
I have designed and built accelerometer amplifier circuits and can offer you advice once we have established some basic parameters.
Regards
Keith
 
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jpanhalt

Joined Jan 18, 2008
9,755
Hello people ,
I dont know if my question is under the correct category but anyway

I need to design a very basic accelerometer circuit . The point is to take the voltage measuerement that a capacitive accelerometer provides and after proccessing it to output it .
The circuit will probably only consist of a few capacitors and resistors , an A/D converter ,an amp and integrators.
I have searched a lot online and have found very few info about such a topic , most are about the construction of the accelerometer. I have a some knowledge about op-amps(integrator,differentiator) and signals.
So if anyone can explain how and why things happen i would be very happy.

P.S i am talking about a diagram not any actual sensors , its more about understanding the concept
Please clarify. At one point, you are talking about outputting a voltage; later, a digital signal. Which is it? A digital signal will need a communication protocol, probably serial, and some sort of MCU most likely.
 

Thread Starter

dimV

Joined Jun 20, 2020
3
Thank you very much for your answers , i am really happy that i can find some assistance and i will try to clarify the best i can.

The accelerometer will be designed from the start. Only the capacitors are available and their output

The method is referred as differential capacitive sensing.

The output of the capacitors needs to get into a differential op-amp or a transimpedence amplifier so we can get the difference. After getting this measumerement, we need to make it as linear as possible and nullify any parasitic capacitance(miller theorem?)

I guess :
The linearity will be achieved with some sort of feedback loop
The parasitic capacities will be nullified by a cascode

As an output , we need the g force measurement in digital form(A/D converter)
Any kind of filter and op amp can also be used .

I am trying to form the question as clearly as possible but since i do not understand it very well it is somewhat diffucult to do so.

P.S By the way , this was a question for better understanding sensors in my class of microelectronics and i have started studying it again because i finally got into my sector.. but while i can get the grasp of it , i cant form a whole answer.

Characteristics: the accelerometer needs to measure up to 50g for an airbag
inside a car that constanly produces up to 2g . Frequency range of the sensor
should be 400Hz .
 

jpanhalt

Joined Jan 18, 2008
9,755
It does seem like "homework" as such devices are readily available, cheap, and robust enough for airbag deployment.

Most accelerometers seem to be based on a moving object, e.g., a ball, lever, or pendulum. A company named Memsic (memsic.com) in Massachusetts developed a series of accelormeters based on movement of a heated gas. One of its big advantages is resistance to extreme, out of range accelerations. They worked at either 100 Hz or 400 Hz.

About 8 years ago, I was interested in its products. Its early application notes had a lot of background theory, but unfortunately, they do not seem to be on the internet (easily) any more. I have up loaded the first three that concentrate on theory. My files have a total of 15. Maybe more are available now. If you need more, you might contact one of these sources:

http://www.memsic.com/accelerometers/
https://www.yumpu.com/en/document/read/18700533/application-note-an-00mx-001-responsive-environments-group

What sort of fluid/gas are you using or is the capacitance change based on something solid?
 

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Thread Starter

dimV

Joined Jun 20, 2020
3
It does seem like "homework" as such devices are readily available, cheap, and robust enough for airbag deployment.

Most accelerometers seem to be based on a moving object, e.g., a ball, lever, or pendulum. A company named Memsic (memsic.com) in Massachusetts developed a series of accelormeters based on movement of a heated gas. One of its big advantages is resistance to extreme, out of range accelerations. They worked at either 100 Hz or 400 Hz.

About 8 years ago, I was interested in its products. Its early application notes had a lot of background theory, but unfortunately, they do not seem to be on the internet (easily) any more. I have up loaded the first three that concentrate on theory. My files have a total of 15. Maybe more are available now. If you need more, you might contact one of these sources:

http://www.memsic.com/accelerometers/
https://www.yumpu.com/en/document/read/18700533/application-note-an-00mx-001-responsive-environments-group

What sort of fluid/gas are you using or is the capacitance change based on something solid?
Ok, these are great help. I quickly glanced over them and they seem really helpful . Thanks for the effort .
 
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