Sociable Objects Workshop: Doorbell Project

The doorbell exercise was flexible: we could do something elaborate or simple. In an elaborate situation, a feedback mechanism, like an LED, could be implemented so that the person triggering the remote doorbell would be notified if a sound was actually generated on the remote end.

A simple doorbell would simply trigger a sound remotely.

I originally did the elaborate doorbell, but the photocell I used to trigger the doorbell was too noisy, even with a 2– and 3–point smoothing function. Thus, I relegated the doorbell to a simple mechanism: a force–sensing resistor, or FSR, as the triggering mechanism and a small speaker as the bell. I don't have images, as my computer reached its end of life before this write up. However, you can imagine the setup: an Arduino, connections for power, ground, transmit, and receive, an XBee, and an FSR in the sender case or a speaker in the receiver case. Both units were powered by 3.6 volts generated by three rechargeable AA batteries connected in parallel.

To make the project a little more interesting, I connected my speaker to the PWM pin of the target Arduino, which is pin 9, and connected my FSR to pin 3 of the source Arduino. This configuration allowed the user to raise or lower the pitch of the speaker with the pressure he or she exerted on the FSR, instead of simply turning on/off a sound by connecting the speaker to a digital pin.

To increase the responsiveness of both radios, I raised the baud rate of the Arduinos to 38400.