SparkFun Forums

[bob123]

I am building a stopwatch timer for a game.
At the start someone passes a Photoelectric Sensor and the timer needs to stop when a ship's bell is rang,

What would be a good way to detect the ringing of the bell?

[jremington]

Put a switch on whatever rings the bell, or tap into the bell circuitry.
It is surprisingly difficult to reliably detect a particular sound.

[bob123]

It's a person ringing a bell, so I cannot tap into that.

[lyndon]

It's a person ringing a bell, so I cannot tap into that.

Stick a little piezo sensor onto the inside of the bell to detect vibration.

[bob123]

I will try a piezo sensor.

The next questions I will have experiment with, because I have no experience with the readings of this sensor.

Will it be possible to see the difference between the swinging and the actual ringing of the bell?
How will surrounding sounds affect the readings?

[lyndon]

No, it is not that sensitive. You'll get a signal when the bell is struck. Nothing else should trigger it.

[jremington]

It's a person ringing a bell

Could that person be persuaded to also push a button?

[bob123]

It's a person ringing a bell

Could that person be persuaded to also push a button?

We could try, but it would be really bad for the game. This is the situation, I should have added the picture before

No, it is not that sensitive. You'll get a signal when the bell is struck. Nothing else should trigger it.

Sounds good.

[lyndon]

Did you ever try the piezo sensor? Curious to know if it worked in that application.

[Valen]

Since those bells are metal I'd try to detect a temporary conduction path. Hang the dangling part (don't know what it is called in English, hammer maybe?) inside the bell with something non-conductive. Connect one side to ground, while the other side is connected to your timer (which is pulled up to a 'digital high' voltage). When contact is made the timer input would glitch down in voltage to ground. But with water all around you might get false positives fooling the timer. (Or suffer from bad contacts due to corroded surface.)

[bob123]

Did you ever try the piezo sensor? Curious to know if it worked in that application.

Yes, I did. I have attached 4 small piezo elements to the outside of the bell.

I have had some issues with interference in the signal I get from them. At first I used a 1M pull-down resistor on each sensor, but there was a buildup in noise on the signals.
So I replaced them for a 22k resistor and that seemed to do the trick.

The competition was yesterday and everything worked fine for the first 2 hours. After that there was a lot of noise again. The bell got quite a beating and there was probably an issue with water somewhere near the piezo elements. After a cleanup and replacing some tape, everything worked great for the rest of the day, except some people that didn't hit the bell hard enough.

For the ones that are interested in the entire project:
I created a scoreboard with three 30cm 7-segment LED displays. In the scoreboard is an arduino that drives the displays and calculates the time.
At the start is a retroreflective lightsensor, running through this starts the time.
There are 4 small piezo sensors on the bell, that stop the time.
Bell and lightsensors are each connected through a 25 meter UTP cable.