Force sensors

[GreekPIC]

Me and my crazy ideas again!

I want to make a realistic replica of the F-16 SSC (actually a joystick which doesn't move).

I found these sensors:http://www.tekscan.com/flexiforce/specs_flexiforce.html

I want to make some changes:
I want 2 sensors per axis. When the stick is centered both sensors should be slightly preloaded and the output should be 2.5V. When it is pushed hard to one side it should give 0V and at the other 5V.

Also the MC34071 opamp is hard for me to find. I have an LM324 and a LM2904 in my spare box. Could I do something with those?

Thanks in advance, Nikolas

 

[MP1]

LM324 should be ok for this application.

MP

 

[GreekPIC]

I thought so, it is quad so 2 axes x 2 sensors is what I need.

But could you give me a schematic? I have never used an opamp before. How can I make the voltage go from 2.5 to 0V when one sensor is pressed and from 2.5 to 5V when the second is pressed?

View attachment 36104

 

[MP1]

I would recommend that you just use the schematic provided from the site you have posted the link. The LM324 will work in place of the one in the article.

Looks like this sensor is a variable resistance output. If so, you can use it as one leg of a resistor divider and calculate your voltage. Basically, the ratio of the feedback resistor to the input resistor is your amplification on an op-amp. So, if you use the sensor in the feedback loop, you can calculate the other resistance so that it gives you the gain you want.
I have attached some info that will help you get started with op-amps.

MP

Opamp.pdf

 

[GreekPIC]

Thanks MP, I got some reading to do now...

As for the circuit what I meant was this: as it is I can adjust the gain so that the voltage will go from 0V to 5V at full pressure. I could use one sensor per axis set up mechanically in a way that in the rest position the stick applies enough pressure to give 2.5V. That position would be difficult to calibrate and even more so to keep calibrated.

Thats why I want to use 2 sensors per axis, so that in the center position the stick will press neither. Pushing on one side will press one sensor (and give 0V at max oressure) and pushing on the other side will press the other (and give 5V).

Hope I explained it well enough

Nikolas

 

[ante1]

Hi Nicolas, MP,

I use the LMC660 for strain gauges, it appears to be more suitable for this purpose than the LM324. I have tried both of them and the results have been much better whit the LMC660. I am not saying that the LM324 is not going to work here but if you can get the LMC660 you should try it.

 

[MP1]

Ante, please tell us about your comparison. What differences have you noted. I have not used the LMC660 in any application and so I am curious about what you have found.

MP

 

[ante1]

MP,

I haven