make an easy fridge's door warning with simple parts.
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Step 1: Circuit Schematic
- 555 timer
- 2N5551 trancistor
- 2x 1k resistors
- 170k resistor
- 100uF capacitor (change this to change the delay)
- 0.1uF capacitor
- normanly open switch
- TMB12A12 beeper
- LRV08 12v battery
Step 2: The Pcb
print the pcb with express pcb and drill the holes
Step 3: Solder the Parts
solder all parts and test it
this circuit wait you about 25 seconds to close the fridge's door
Step 4: Paint the Pcb
paint the pcb with a color or lacquer spray to protect the copper
Step 5: The Box
find a box for the project or download the .stl files and print them works with N O switch
Step 6: Assemble It
put the pcb into the box and glue it with instant glue
add at the back of the box a two side tape
Step 7: It's Ready
put the battery , the cover and its is ready
Step 8: End
when the led is on the door is open and the battery is ok
if you close the door the (normanly open) swich, the circuit is turned off and you dont worry for the battery
the 555 needs 10 mA and the beeper needs 25 mA if the beeper turned on
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