How to trigger an old-style, twin-bell alarm clock?

jtrz

Hi all,

I was wondering if any of you could help me out here?

I am designing a circuit for a friend who is a magician.· Basically, it's an Ultrasonic PING sensor that, when tripped, sets off an old-style, twin-bell alarm clock.· The authentic ring is what he wants to hear from the alarm.· The guts of this would be hidden away.

He·wants it to ring as long as he's tripping the sensor then stop when he moves out of the beam.··This should be done until the "flywheel" (? wind-up mechanism ?) on the clock/bell-mechanism runs out of power.· This means that he can do this 3-4-5 times.· Timing is up to him (to get out of the beam).· But it should basically be considered to be done a few times on a "full wind-up."
I have that working with a simple LED to substitute for the ringing the bell.· I also have the beam distance able to be calibrated with the turn of a pot (I think...been a while since I started this).

But here's my problem:· the clock mechanism is a wind-up one.· How would·I start and stop the ring of the bell?

Can anyone suggest a solution OR maybe another way to do this with a different typs of alarm mechanism?· Is there one that anyone knows of that has some type of digital interface and is already set up to do this?

BTW we cannot substitute a larger firebell or schoolbell for this.· It needs to be the size and esp the sound of an alarm clock.

Thanks in advance for any help!

John

Phil Pilgrim (PhiPi)

When the bell on one of these alarms rings, the winder that tightens the spring rotates. When the spring has run down, you can even force more "ring" out of the clock by turning the winder in that same direction, which is opposite the direction of winding. If you don't mind digging into the clock's guts, you could remove or disable the spring and attach a continuous-rotation servo to the winder. To ring the alarm, just drive the servo. This would also alleviate having to worry about how much spring tension remains.

The other option would be to use a regular servo to pull and push the alarm enable button (the thing you pull out at night and push in in the morning to stop the infernal ringing).

-Phil

jtrz

Thanks Phil - I kind of thought I would have to take apart the clock to use the bells and the ringer mechanism. I like your first thought about using a continuous-rotation servo.

erco

The alarm ringer is just a highly-geared mechanical escapement, like a fast-moving pendulum that toggles between two bells. All you have to do to stop it is stick something into its path to block the motion, and then pull it out to resume ringing. Not a lot of force is required to slide a pin/arm in & out perpendicular to the ringer's path. You could use a tiny servo arm, or even a small solenoid: have the plunger block the ringer. A small solenoid would consume more current than a servo, but is smaller and might fit into the case without extensive mods.

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·"If you build it, they will come."

DaveG

Another approach would be to digitally record the sound of the bell and play it back through a hidden speaker.
Jameco has a record/playback kit #645335 that records 20 seconds of sound. The kit includes a speaker. It probably
could be triggered by the Stamp to playback the ring as many times as you want.

There are many other chips/kits out there that can record for much longer times, can record multiple sounds, and can play
them back individually, at will.

Dave G