Let's Make Robots!

BEAM tactile sensor

I'm really attracted by these antennae-shaped tactile sensors: http://letsmakerobots.com/node/7542

The problem is that I cannot figure out how to use 'em! I mean, how the contact between those sensors and an obstacle would cause an I/O pin to toggle?

 Thank you in advance for the hints you would give me.

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Thank you all,

 Much clearer now!

I did a tip/walkthrough on making antenna like that but with red/green LEDs that change colour when the antenna touches something. Look here: http://letsmakerobots.com/node/7298

There is a schematic diagram and video of it working. Paperclips make good antenna when straightened ;)

The idea is that you solder the pin to your PCB, and then solder the spring on so that the pin sits inside the spring without touching the sides. As wayland said, a small force exerted on the antenna causes the spring and pin to contact each other closing the switch.

To trigger an input pin you need to add a few things:
• Connect the pin or spring to either V+ or ground. Using V+ will make an active high switch, using ground will make an active low switch.
• Connect the spring or pin that you didn't use in the previous step to a resistor of a reasonably large value, 20kΩ is quite a common choice.
• Connect the other end of the resistor to either ground or V+, whichever is the opposite of what you used in the first step.
• Connect the spring or pin that you used in the second step to you input pin.

When the switch is open (no contact) the pull-up/pull-down resistor will set the input pin to high/low. As soon as the switch closes, the pin will be connected to ground/V+, changing the state of the pin. The pull-up/pull-down resistor ensure that when the switch opens again the pin goes back to the default state.
Finally, you can omit the pull-up/pull-down resistor if your microcontroller has one built into the port you're using already.

something hitting the antenna causes the spring to bend a little bit, putting it in contact with the pin and completing the circuit. I had a little trouble figuring these out too.