# accelerometer negative voltage

Discussion in 'General Electronics Chat' started by zacharoni16, Feb 16, 2013.

1. ### zacharoni16 Thread Starter New Member

Feb 16, 2013
2
0
I am working on a project that I require negative voltage for -acceleration and positive voltage for +acceleration

I am using a KXPS5-3157 accelerometer in analog mode.

Data sheet: http://www.futurebots.com/3157.pdf

While at rest, the accelerometer outputs a voltage equal to VCC/2

so 3.3V supply 0G's will be 1.65Volts, the sensitivity per G is 440mV per G

I was thinking I could design an opamp to "zero" the accelerometer at 1.65 volts, then the negative and positive voltages will come out of the opamp @ 440mv per G sensitivity

I need to cancel out gravity in the Z axis which is 1G, so thats 2.09 Volts to zero out for the Z axis

(1.65 + 0.440) volts

My run at the circuit:

My problem is I have +12V, +5V, and +3.3V available, but I don't have any negative supply voltage for -3.3V and + 3.3V

I was wondering if it's possible to design a single supply opamp that would do the same thing with a virtual ground??

using a potentiometer to zero it out, but in multisim I couldn't get it down to exactly zero

I have a bunch of mcp601 opamps, they are rail to rail single supply opamps

Any help is appreciated

Last edited: Feb 16, 2013
2. ### m121212 Active Member

Jul 24, 2011
81
0
You're going to need a negative supply to correctly level shift. You can get a negative supply by building a small buck converter to convert +3.3V to -3.3V. Check out the spec sheet for the MC34063. All you need is a few passive components and a tight board layout.

Another option is to think of a way around your requirement to have a negative voltage for a negative acceleration.