Calls do not always work properly in an educational institution. In this case, the teacher needs a timer that signals the end of the lesson exactly 45 minutes after starting. This is more convenient than periodically distracted to look at the clock.
Instructions
Step 1
Find a defective microwave oven that cannot be repaired. It must be electronically controlled (mechanical timers do not have the required accuracy).
Step 2
Leave the oven unplugged for at least a week. This is necessary to discharge the high-voltage capacitor present in it.
Step 3
Open the oven body. Despite the fact that the high-voltage capacitor is now most likely in a discharged state, still do not touch it or any other power parts of the furnace: a magnetron, a large power transformer, a high-voltage diode.
Step 4
Disconnect all connectors carefully from the front panel. Remove it along with the board and keyboard.
Step 5
The front panel has its own small power transformer. Connect to its primary winding, rated for 220 (not 110!) Volts, a cord with a plug through a 0.25 ampere fuse. Thoroughly insulate all connections, secure the fuse holder and cord securely.
Step 6
Place the panel in a small enclosure so that no parts on the back are touched.
Step 7
Connect the plug to a power outlet. Try to set the shutter speed from the keyboard and start the timer. When it ends, you will hear three loud beeps.
Step 8
If the buttons that are necessary to set the timer have deteriorated and do not respond to pressing, disconnect the timer from the mains, connect new buttons in parallel to them and place them separately on the case. Then close the case and test the operation of these buttons.
Step 9
Before conducting the classroom session, plug in the timer and set the shutter speed to 45 minutes. Start teaching when your schedule calls for it, using your normal watch and start the timer at the same time. Do not turn the electronic board towards the audience. When it’s time to end the lesson, you and your students will hear three loud beeps.
