Circuit close-up
Date/Time: 2006:04:24 18:48:24
The door knob alarm circuit close-up. It has been modified to light up an LED instead of buzzing a buzzer. (For photographic purposes.)
The oscillator
Date: 04/25/2006
These are the pulses oscillating to the sensor. I modified the circuit so they are closer together in this capture. In reality they time between them is about twice as much.
Uncalibrated triggers
Date: 04/25/2006
The voltage at the clock and 'D' trigger of the flip-flop. The blue trace is triggering the flip-flop first, so the alarm is off. When the sensor is touched, the blue trace [url=http://superpositioned.com/gallery/v/doorknob/touched.png.html]drops[/url] and the yellow trace triggers the alarm to go off first.
The calibrated response
Date: 04/25/2006
In order for the sensor to work, you need to adjust the potentiometer so the blue trace is [i]just above[/i] the yellow trace. When the knob is touched and the blue trace falls, it will be sure to go below the yellow trace.
You can do this by turning the potentiometer until just after the alarm goes off.
Door knob touched
Date: 04/25/2006
When the door knob is grounded, the blue trace takes longer to charge. Therefore, the yellow trace triggers the flip-flop first.
When touching the knob, the trace does not drop this far. I grabbed right onto the wire. Touching the doorknob does not cause as much noise either.
Wired up
Date/Time: 2006:04:24 18:47:53
The alarm is wired up to a doorknob in this photo. As you can see, the knob is not being touched and the LED is not lit up.
Alarm Tripped 1
Date/Time: 2006:04:24 18:52:36
I'm touching the doorknob in this photo and the alarm tripped. The LED is lit up!
Alarm Tripped 2
Date/Time: 2006:04:24 18:52:43
I'm touching the doorknob in this photo and the alarm tripped. The LED is lit up!
