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Step 11Test how well it works and debug the problems.
We rode out to dinner to try the light out. In the daytime it stayed off and it started working at dusk. However, there were two problems: the vibration sensor was not nearly sensitive enough, and the light didn't blink all the time -- in fact, barely at all.
The first problem was an easy fix: add some weight to the top of the spring. I soldered on a small segment of copper wire and that made it so sensitive that you could barely hold it and walk down stairs without it detecting enough vibration to turn on.
The second problem was much more difficult. I debugged the circuit with my oscilloscope and determined there were a couple minor wiring problems. This could have been much easier if I had tested it once I wired up the 555 part of the circuit. I fixed everything I could but it just wouldn't function correctly.
I finally gave up. I think the 555 can't handle an input voltage that decreases fairly rapidly (about 0.1 volts per second, so the 9 volt initial input would drop to zero after 90 seconds or so.) This may be because the internal reference voltage it uses to detect when to toggle may stay higher than it should and therefore the capacitor will never charge to a high enough voltage to cause its internal flip-flop to trigger and drive the output low.
To get around the problem, I removed the 555 and ran a jumper from the V+ input at pin 8 to the output at pin 3. Now the light stays on steady and slowly decreases in brightness until it finally extinguishes after a few minutes.
The first problem was an easy fix: add some weight to the top of the spring. I soldered on a small segment of copper wire and that made it so sensitive that you could barely hold it and walk down stairs without it detecting enough vibration to turn on.
The second problem was much more difficult. I debugged the circuit with my oscilloscope and determined there were a couple minor wiring problems. This could have been much easier if I had tested it once I wired up the 555 part of the circuit. I fixed everything I could but it just wouldn't function correctly.
I finally gave up. I think the 555 can't handle an input voltage that decreases fairly rapidly (about 0.1 volts per second, so the 9 volt initial input would drop to zero after 90 seconds or so.) This may be because the internal reference voltage it uses to detect when to toggle may stay higher than it should and therefore the capacitor will never charge to a high enough voltage to cause its internal flip-flop to trigger and drive the output low.
To get around the problem, I removed the 555 and ran a jumper from the V+ input at pin 8 to the output at pin 3. Now the light stays on steady and slowly decreases in brightness until it finally extinguishes after a few minutes.
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