Monday, February 7, 2011

Project 11 - Piezo Sounder Alarm

Project 11 is very simple to wire up... and the program is one of the shortest we've seen so far. It uses a sine wave, again, to generate values that fluctuate, allowing the piezo buzzer to warble like an alarm.

I've got the sound from the unedited program playing in the first video. It's loud... and obnoxious. This would definitely annoy a brother or sister who entered your room without permission! I modified the variable value to start with a base of 1000 (instead of 2000) and the alarm has a lower tone... but still loud.

I'm amazed at the volume generated from this tiny device - it was the smallest one in the bins at Radio Shack. I'm sure the larger ones require more voltage, but little fella is rated for between 3 and 20 volts. I'm glad I'm not hitting it with 20 volts!

1 comment:

  1. What grabbed me about this one was how much easier it was to vary the tone and the duration of the pulses compared to the PUT and 555 based oscillators in the Make:Electronics book.

    Much as I appreciate the combination of mathematics and black arts of tuning an oscillator with an RC circuit, microcontrollers make this so much easier.

    With the help of my eight year old, I verified that children can hear much higher frequency sounds than adults. I modified the code to produce alternating higher and lower pulses and we added a serial interface that would change the pitch of the two tones, keeping them about 2000Khz apart. (Kind of "Beeeep....Boooop....Beeeep...Boooop...") I kept stepping up the frequency until I could hear only the lower tone, but my son could hear both.

    I don't have the data in front of me, but my kid could still hear both tones even after they were too high for me. I also noticed a range near the high frequency end where my hearing dropped out and then returned, a so called "aviator's" or "gunner's notch", no doubt from running power tools without ear protection during my construction worker days.

    So anyway, now I am adding a "Do it yourself audiometer" to the list of hands on demo projects to set up in my classroom.