Modifying a water sensor

[holobean]

okey i took this ckt from a hobby kit book. i know the 555 timer is working in astable mode and give an output of square wave at pin3 everytime the water sensor is activated and 0V when the water sensor is off. Now my problem is i don't want a square wave but a constant 5V output once the sensor is activated and to achieve this i know we can just change it to monostable mode. but the problem is that the monostable mode give me 5v when its activated and stays there 5V unless reseted/triggered at pin4. Now my question is how can u make a output of constant 5V when sensor is activated and 0V once the sensor is not detecting water anymore w/o supplying external trigger to the ckt in monostable mode? or unless you better idea on how to modify this plz suggest!!

 

[mramos1]

What are you tring to drive with the output? Can you change the duty cycle and get by? Or add an RC to charge up with the frequency coming out?

Also, avoid BMP files, they are very large, use jpg or png.

 

[Blueteeth]

Hi,

I realise you want it as simple as possible..I'm just unsure as to why you are using a 555 timer.

From what I've read, you simply want a small circuit that makes the output 'high' whenever the two wires are imersed in water...correct? Now, even though 'pure' water has a pretty high resistance., no connection has virtually infinate resistance. So all you need is something that detects this change in resistance. I would say, a comparator or a transistor amplifier.

heres some links that may help:

**broken link removed**
**broken link removed** - uses comparators.

**broken link removed** - you only need one probe.

I also believe logic inverters are sensitive enough to detect the smaall current that flows through the water...I mean, if you leave their inputs unconnected the output goes crazy. So a pullup/down resistor should be used.

Hope this helps,

Blueteeth

 

[holobean]

What are you tring to drive with the output? Can you change the duty cycle and get by? Or add an RC to charge up with the frequency coming out?

Also, avoid BMP files, they are very large, use jpg or png.

Well im actually going to connect the output to the a parallel port.. enough to drive the the port to on state.

 

[holobean]

Hi,

I realise you want it as simple as possible..I'm just unsure as to why you are using a 555 timer.

From what I've read, you simply want a small circuit that makes the output 'high' whenever the two wires are imersed in water...correct? Now, even though 'pure' water has a pretty high resistance., no connection has virtually infinate resistance. So all you need is something that detects this change in resistance. I would say, a comparator or a transistor amplifier.

heres some links that may help:

**broken link removed**
**broken link removed** - uses comparators.

**broken link removed** - you only need one probe.

I also believe logic inverters are sensitive enough to detect the smaall current that flows through the water...I mean, if you leave their inputs unconnected the output goes crazy. So a pullup/down resistor should be used.

Hope this helps,

Blueteeth

Thanks for your websites.. but i don have time to reconstuct a new circuit, im having a presentation this week. At first the original ckt was to sound a speaker and im not using this speaker output instead im using it to supply to the parallel port to give me a on state thats all. I know its giving out a square wave which i don't want. i prefer it gave out 5V constant and 0V. as it would be easier on my programming part. It would be great if you guys could modify this ckt instead

 

[mramos1]

Oh, I see what you are doing now.. Slow the 555 down real slow and the printer port will catch one of the highs.. Tie it to paper out of something, check to see if it is inverted when you do. That will work, input that register, mask the other bits off and if not 0 then you have a 1 (5V) on the pin.