Interfacing with force sensors

Forum 2005-2010 (read only) Hardware Interfacing
1

I'm new to the arduino(and ee in general), but I've been programming forever.

What I'm trying to do is put 3 to 4 force sensors inside a football helmet so that when the helmet is hit from different angles it can record the force exerted by each blow.

I'm trying to hook up the arduino to a force sensor, specifically this one:
http://www.trossenrobotics.com/flexiforce-100lb-resistive-force-sensor.aspx

Is this the right direction to go with this project or will a force sensor like this not work very well when it is embedded into a helmet?

Could I just run a 5 volt output straight from the arduino to this force sensor and then feed the output straight into an analog input on the arduino? Or do I need some kind of circuit in between the sensor and the arduino?

2

Hi,

use the recommended drive circuit from the web site of your link and
connect the output of the circuit to a 1k resistor, the other pin of the resistor to an analog input pin of the arduino.
Read the analog input and divide the value by 9, this will give you the force in lbs (approx).

Mike

3

Is the triangle in this circuit diagram representing the Arduino? Also the middle pin of the force sensor goes to X, what does that mean? Also how can you tell it needs a 1k resistor and that I should divide by 9?

Thanks so much for the help so far.

4

Does anyone have any idea what the triangle stands for in this circuit?


Is that where I would put the arduino?

Also answers to any of the other questions above would be great.

Thanks

5

The triangle is an operational amplifier.

However if I was doing the project I would use a accelerometer
http://www.dimensionengineering.com/accelerometers.htm

Also how can you tell it needs a 1k resistor and that I should divide by 9?

You don't need just a resistor you have to prevent negative voltages getting into the Arduino so you also need some camping diodes.
See:- http://www.thebox.myzen.co.uk/Tutorial/Protection.html

As to the divide by 9 it actually depends on what you have as the Rref value. You can see what to divide by by looking at the graph in the data sheet.

In fact I wouldn't use the circuit with the op-amp there is no need. Connect it like you see in this:-
http://protolab.pbworks.com/TutorialSensors

6

I am not 100%, but I think the x on the middle pin means thert is no connection. I just read somehting on a site today that mentioned that. Will update this post if I can find it

7

Doh! Memory of a goldfish, the trossen link you posted has a paragraph headed construction the last line says "two outer pins of the connector are active and the center pin is inactive."
So I would assume X means no connect