Simple Water Level Detector Using a LM555 in Astable Mode:

Materials:

1. One LM555
2. Two 330 Ohms resistors
3. One red LED
4. One green LED
5. One 10 nF capacitor
6. One 100 uF capacitor
7. One 1 KOhms resistor
8. One 100 Ohms resistor
9. Wires for connections
10. Protoboard
11. 9 volts battery
12. 9 volts battery connector
13. Cutting pliers
14. Transparent glass
15. Water

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1. Connect in the protoboard the following circuit:

2. Connect LM555 terminal 1 to GND.

3. Connect LM555 terminals 4 and 8 to the 9 volts battery positive terminal.

4. Connect LM555 terminals 2 and 6.

5. Connect one terminal of R1 to LM555 terminal 7.
6. The other terminal of R1 should be left free for one of the open terminals connection.

7. Connect R2 between LM555 terminals 6 and 7.

8. Connect the other terminal of R2 to the possitive terminal of C1.

9. Connect the negative  terminal of C1 to GND.

10. Connect LM555 terminal 5 to a 10 nF capacitor.

11. Then connect the free terminal of the 10 nF to GND.

12. Connect LM555 terminal 3 to R4.

13. Connect the negative terminal of D2 to R4.

14. Connect the positive terminal of D2 to the 9 volts battery positive terminal.

15. Connect R3 to GND.

16. Connect the free terminal of R3 to the negative terminal of D1.

17. Connect D1 positive terminal to the 9 volts battery positive terminal.

18. Connect the free R1 terminal to one of the open terminals.

19. Place the other end of the terminal with tape at a specified level of the glass.

20. Place the other open terminal with tape at the bottom of the glass.

21. Connect the other end of the open terminal to the positive terminal of the 9 volts battery.

22. Turn the circuit on by connecting the 9 volts battery.

23. The green LED will turn on indicating the circuit/device is on.

24. Pour water into the glass and, once the water level reaches the higher open terminal, the red LED will start to flash.

When the open terminals aren’t closed the red LED D2 will be off. It is intended for the open terminals to be closed with a determined water level. Once the water lever reaches the desired quantity, the water will close the open terminals (or this part of the circuit) and, as the LM555 is configured in Astable mode, the LM555 output (terminal 3) will send a continuous squared wave form into D2 which will make the red LED to flash at a determined frequency. The frecuency of the squared wave is determined by the values of R1, R2, C1 and the impedance of the water.