Water Activated Alarm - Electronic Circuits Projects Diagrams Free

**ElectroMaster** · 25th July 2002, 01:21 AM

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).

wolverin · 13th November 2005, 03:43 PM

I bulit this circuit on electronic workbench...but this is not working....plz have a look at it and tell me where i went wrong.

**Nigel Goodwin** · 13th November 2005, 03:56 PM

What's the changeover switch for?, that wasn't on the original circuit!.

You need to add a resistor between base and collector of the transistor, to simulate the resistance of the water.

wolverin · 13th November 2005, 07:12 PM

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????

**Nigel Goodwin** · 13th November 2005, 08:17 PM

Quote:

Originally Posted by wolverin

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????

Either should work.

wolverin · 13th November 2005, 09:26 PM

Can somebody plz send me a working schematic circuit of this one on EWB file plz.....i am so dumb tht i cud not make either of this work.

But i'm really intrested to do this one as my project.

audioguru · 13th November 2005, 10:32 PM

The 1st circuit will work if you wire the transistor as shown in the original schematic and use a speaker instead of a buzzer.

The 2nd circuit will work if you wire all parts like in the schematic.

mstechca · 14th November 2005, 01:37 AM

Quote:

Originally Posted by wolverin

I bulit this circuit on electronic workbench...but this is not working....plz have a look at it and tell me where i went wrong.

Is it just me, or is everyone noticing that the ground symbol is connected to nothing :?:

Connect ground to the -ve terminal on the battery.

AllVol · 22nd November 2005, 05:20 PM

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:

rancid rock · 18th January 2006, 04:23 AM

hmmm....would there be a way to modify the sensortivity of the water sensors?, so it only works when the sensors are a certain amount of wetness?

audioguru · 18th January 2006, 04:36 AM

Quote:

Originally Posted by rancid rock

hmmm....would there be a way to modify the sensortivity of the water sensors?, so it only works when the sensors are a certain amount of wetness?

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.

rancid rock · 19th January 2006, 03:29 AM

nice!!!, thx man

uski · 2nd April 2006, 05:32 PM

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

).

uski

3rd April 2006, 02:31 AM

yes mistakeca, its just you.

tunde1 · 26th May 2006, 10:10 PM

do u have a circuit diagram on this. tested and working

25th July 2002, 01:21 AM	(permalink)
ElectroMaster Administrator	Water Activated Alarm 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). __________________ Electro Tech Online Owner - PM me if you find a problem! Email verification didn't arrive? Click here. (PLEASE DO NOT ASK ME FOR CIRCUITS OR PARTS - I WILL NOT ANSWER)

13th November 2005, 03:56 PM	(permalink)
Nigel Goodwin Super Moderator	What's the changeover switch for?, that wasn't on the original circuit!. You need to add a resistor between base and collector of the transistor, to simulate the resistance of the water. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

13th November 2005, 10:32 PM	(permalink)
audioguru Experienced Member	The 1st circuit will work if you wire the transistor as shown in the original schematic and use a speaker instead of a buzzer. The 2nd circuit will work if you wire all parts like in the schematic. __________________ Uncle $crooge

18th January 2006, 04:23 AM	(permalink)
rancid rock Experienced Member	hmmm....would there be a way to modify the sensortivity of the water sensors?, so it only works when the sensors are a certain amount of wetness? __________________ <( \"<)....kirby!!!....0==[=====>

19th January 2006, 03:29 AM	(permalink)
rancid rock Experienced Member	nice!!!, thx man __________________ <( \"<)....kirby!!!....0==[=====>

13th November 2005, 09:26 PM	(permalink)
wolverin New Member	Can somebody plz send me a working schematic circuit of this one on EWB file plz.....i am so dumb tht i cud not make either of this work. But i'm really intrested to do this one as my project.

22nd November 2005, 05:20 PM	(permalink)
AllVol Experienced Member	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:

2nd April 2006, 05:32 PM	(permalink)
uski New Member	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 ). uski

3rd April 2006, 02:31 AM	(permalink)
hyedenny Guest	yes mistakeca, its just you.

26th May 2006, 10:10 PM	(permalink)
tunde1 New Member	water activated alarm do u have a circuit diagram on this. tested and working

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