The circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, the transistor will have no bias current and be fully off. However as the probes get wet the transistor will conduct and sounding the alarm.
An On/Off switch is provided and remember to use a non-reactive metal for the probe contacts. Gold or silver plated contacts from an old relay may be used, however a cheap alternative is to wire alternate copper strips from a piece of veroboard. These will eventually oxidize over but as very little current is flowing in the base circuit, the higher impedance caused by oxidization is not important. No base resistor is necessary as the transistor is in emitter follower, current limit being the impedance at the emitter (the oscillator circuit).
I found this circuit diagram for the same water activate alarm in other site...Every compononets are similar but the one capacitor from node 5 is missing in the above circuit...Have a look...which one works????
I found this circuit diagram for the same water activate alarm in other site...Every compononets are similar but the one capacitor from node 5 is missing in the above circuit...Have a look...which one works????
You have no sensor contacts on the base of your transistor. In your version, you are simply switching +9volts from collector to base. The contacts (green dots in the original) when activated by moisture, supply the small current necessary to allow the larger current to flow through the collector-emitter circuit of the transistor. This then provides the Vcc to turn on the 555 timer and allow it to oscillate. :roll:
Change the 10k resistor to 100k, the 56k resistor to 560k and the 0.01uF capacitor to 0.001uF. Then it will be 10 times more sensitive.
Change the 10k resistor to 1k, the 56k resistor to 5.6k and the capacitor to 0.1uF. Then it will be 10 times less sensitive.
You could also add something conductive to the water like salt or something. Or use distilled water that conducts nearly nothing.
I would suggest using carbon electrodes so as to avoid corrosion and oxydation: aluminium creates a nice insulating layer when it oxydizes and this layer may prevent the alarm from working and it's the same for almost any metal (excluding gold but it's a bit expensive ).
Carbon electrodes can be taken from graphite pencils (sorry english is not my native language and I don't know the simple words ).
Water has some salts in it then it is conductive.
When water is between the contacts in the first circuit then it turns on the transistor that turns on the oscillator.
Can i insert a photocell in this cct to prevent it triggering when rain falls during the night when i am in bed and if so where in the cct should it be best placed without effecting the operation too much.