MEMS

Strain-Guage based Pressure Sensor

I just finished building a self-contained pressure sensing device using a MEMS strain-guage type sensor from Measurement Specialties. Single phase AC goes in one side, and a 0.5V-4.5V signal proportional to pressure input comes out the other side. The sensor has a rated max of 5″ of water.

Pressure 001

The circuit is simple enough, the AC goes through a fuse and into a AC-DC converter. The output is regulated by a 5V regulator, which powers an op-amp and the sensor. The op-amp buffers the output of the sensor. I used a MAX4242 op-amp, as it can run on less than 5V, and has rail to rail inputs and outputs. This keeps my signal in the CMR range.
I have used products from Measurement Specialties in the past, and they seem to be very good products for the money. I have some of their button load cells which were very affordable and also have about twice the output signal (mV/V) of similar load cells from Omega or Futek.

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Saturday, October 10th, 2009 Electronics 2 Comments

MEMS Accelerometers

I recently messed with some accelerometers in order to cancel out dead weight in a load cell application. These MEMS (microelectromechanical systems) devices are really handy. They are incredibly small, they have very modest power requirements, and are typically in a standard IC package. The device that I ended up using was a Freescale MMA1220EG. It offers an on-board amplified output and only requires three external components. It uses 5VDC at 5mA, and has a +/- 8g range. The 0g offset is 2.5V and moves from that point at 250mV/g.
I built a simple PCB that mounted the accelerometer and a filter along with an op-amp as a buffer to drive the output and send it down a run of wire. It worked so well I’ve been trying to think up something else to put one on.

IMAG0094

Sony 003

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Friday, August 28th, 2009 Electronics 4 Comments