Hi there

after much appreciated help with another weather sensor circuit I thought I might as well seek help clearing up a few queries I have with my other projects

As I had mentioned Im rather interested in weather monitoring sensors at the minute. A while back I had hunted down a schematic for a rain sensor/alarm. I originally wanted one where a light would activate when rain bridged the sensor, but the most decent one I could find for what components I had was this one..

I made 2 of these and they work very accurately, as a sensor I used a small piece of perf board with 2 thin copper wires threaded next to each other.
as soon as rain bridges the wires the buzzer honks around once a second or faster/slower depending on how wet,
the disappointing thing about this circuit is that the little 3v buzzers I have used are very quiet when this circuit is activated, I Know this isnt the maximum volume of the buzzer as when tested with a 1.5 battery etc they buzz much louder. In this circuit they make a tiny interval of honks like water dripping from a tap.

Im curious if anybody can tell me how I could replace the buzzer with an LED which would activate in place of the buzzer, OR is there away of increasing the volume of the buzzer.

im also curious if i were to build a particularly different sensor like the one I have drawn below ..

would this adaptation to the sensor make it possible for sensing snowfall rather than rain.

thanks

 

... how I could replace the buzzer with an LED which would activate in place of the buzzer, OR is there away of increasing the volume of the buzzer.

Using an LED would be very simple, just an LED and a resistor to replace the buzzer BUT you need an LED with a low forward voltage. Plenty of LEDs will not light at 3V, especially when that is lowered by battery aging. The resistor is used to limit the current through the LED, and the choice will depend on the specific LED you choose.

Or you could use a joule thief circuit from a solar landscape light. These can use a low voltage and step it up into pulses high enough to light any LED. Just use your 3V supply as the "battery". You can replace the LED with any color.

I think to get to more volume you may need a higher voltage power source.

 

The first thing I would try to increase the volume, is to replace the 1M resistor to the rain sensor with a smaller one. Start with 100K and decrease it down to 1K until you get a satisfactory sound.

 

I'm not so sure that would matter - loading the sensor might draw down the voltage - but now that you mention it, a 470Ω base resistor instead of the 1K might allow more current thru the buzzer.

 

Along with decreasing the 1 meg rain sensor resistor, you could try increasing the value of the 1uf capacitor to increase the beep length. If you have extra 1 uf's just add them in parallel.

 

Thanks for the help guys, I will experiment about a bit with these ideas,

Wayneh, on the subject of using a joule thief circuit to power the LED, Would that mean connecting the Joule thief's positive and negative terminals in place of the buzzer, IE would the power powering the buzzer at the minute then increase through joule thief, powering an LED ??

 

That was my thinking, yes. But not technically the power, just the voltage. Power is reduced by inefficiencies of the circuitry.

 

have to say thanks for making me aware of the joule thief circuit, have made one and im very impressed how this little circuit works.