How to build the simplest Automatic School Bell System (see diagram).

Make with a normal digital timer an ideal and cheap automatic school bell system. (No computer required)

Requirement : The school needs 12 rings per day. The ring duration should be about 6 Sec.

But most of digital timer clocks have 10 switching pairs (On-Off) per day only.
Also the switched time is not less than 1min.
So, this is not useful to function as an automatic school bell in this case.

The solution:
10 switching pairs means that we have 10x switching ON and 10x switching Off.
In this case we use the ON and OFF switching as ON only.
Basically we have now 20 ring possibilities.
(See the simple diagram in the video.)

Program your timer e.g. as follows:

Display ------Time---------Action

On----------08.00----------Ringing for 6Sec
Off----------09.00----------Ringing for 6Sec
On---------10.00-----------Ringing for 6Sec
Off---------11.00-----------Ringing for 6 Sec
etc.

In case you want a longer ringing time change the caps for e.g (approx) 300V 220mF
(Capacitors voltage should not be lower than 300V)
You can find the high voltage capacitors in old computer power supplies.

The 1 kOhm resistor absorbs the peak current during the very first moment of recharging the empty capacitor and avoid sparking of the relay contacts.




The digital timer itself remains in its original state and can be pulled-out and plugged-in into a 220V socket inside the box.
The box is made from two joint emptied dry battery cases.

Originally a digital timer has a small backup battery which, if its gets older, can not cope with a long power-off period during holiday season to keep your settings. Therefore, it's better to use a bigger (rechargeable) one external and to solder the wires directly on the battery.

This system can also be used to extend any similar timer with applications where much switching for short moments are required.

Category:

Science & Technology

Tags:

• Homemade
• Automatic
• School
• Bell
• Reminder
• Switching
• Multiplier
• Digital
• Timer
• DIY
• Simplest
• how
• to
• make