Fiber Feelers Touch Sensor
1) LED - I used IF-E96 which is a visible red LED housed in a convenient connectorless plastic fiber optics package.
2) Phototransistor - I uses IF-D92 which is a phototransistor detector housed in a convenient connectorless plastic fiber optics package.
3) Fiber cable - You want cheap fiber (see description below to see why). I used this fiber cable.
4) 100 ohm resister - This is to regulate the current to your LED. In my system my LED wants 60 milliamps at 5 volts which when I use ohms law is (5/.06) 83 ohms. I rounded this up to the next common resister value of 100 ohms.
5) 440 ohm resister - This divides the voltage for output with the phototransistor. I just experimented with this value until I found a resister that gave my system a good sensitivity.
6) Solderless bread board and wires - This is an easy way to wire up this circuit.
7) Multi meter - I uses a Fluke DMM, but any way to measure voltage would be fine.
8) 5 volt power source - This may be different if your LED requires a different voltage.
Fiber feelers are also sometimes called fiber whiskers. In a nutshell they are a loop of fiber optic cable with light passing through the fiber that makes a very sensitive touch sensor. This project just verifies this is a workable sensor and I read the output voltages with a digital multi meter. I would recommend doing this before hooking it up to your micro controller since this sensor is highly dependent on the quality of fiber you are using. By doing this simple experiment you can save yourself a lot of grief. When you are ready to hook this up to a micro controller all you need to do is use an analog input and look for a change in voltage to detect a collision.
The trickiest part of this project is getting low quality fiber cable. The reason you want low quality fiber is because the idea behind this sensor is when the fiber cable bends the amount of light passed through the cable changes which affect the voltage passed through the phototransistor. If you use high quality fiber cable the amount of light passing through the cable will not change when the cable is bent. It would be nice if the fiber cable was jacketed, but I used unjacketed and then used unshrunk heat-shrink tubing as a jacket. I suspect finding jacketed fiber cable of low quality is more difficult. Leaving the fiber unjacketed seemed to work fine, but I was worried that traveling from a dark to bright room might affect the voltage level passed through the phototransistor, but I did not test this since jacketing it was easy enough.
When playing around with this sensor I determined it is definitely a workable sensor, but it is somewhat finicky and would take some precision work to get it working in a highly reliable manner. The biggest issue I ran into was that the amount of light passed through the fiber cable would not change when with a light touch sometimes. This problem only seemed to show up on of the loop geometries I tried. So you would need to take this into consideration. I haven't eliminated this as a possible sensor, but since I just want a simple bump sensor I'm looking into other less finicky solutions. I've just ordered some flex strips and will evaluate those when I get them. I can totally see using fiber feelers in certain applications though.
Here is the circuit diagrams: Fiber Feelers Circuit Diagram
Here are some pictures: Pic 0, Pic 1
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