This circuit help you to indicate existing letters in mailbox without opening the box's door. the circuit based on IC555 and using infrared ray.
When postman put a letter in the mailbox, the letter cuts the IR ray between IR transmitter and photo-transistor and turn the transistor S9013 ON that connected to pin2 so pin3 of the IC555 become 1 and run the 7-segment display that set to show POST word. but when no letter in the mailbox the 7-segment show 4 dots (. . . .).
When you take your letter from mailbox you have to pushing RESET button or touch pin6.
When you take your letter from mailbox you have to pushing RESET button or touch pin6.
Power consumption of the circuit is very low, about 10mA to 20mA and can run with a small 9v battery.
Parts list:
IC 555
Transistor S9013
Transistor S9012
IR LED
Phototransistor
1 digit 7-segment- common cathode(4pcs)
Note: you can use only four 1digit seven segment and can't use one 4digit seven segment.
Note: you can use only four 1digit seven segment and can't use one 4digit seven segment.
