Water Activated Monostable

[tom08]

Hi again everyone, thanks for all the ideas last time. For those who didnt read it, i am making a duck that quacks and flashes when it is placed on water. (GCSE Electronics). I have the water activated monostable working with a liquid sensor. Trouble is, it keeps going until the sensor is taken out of water (obviously, cause the switch stays closed) Is there any way of making it so that it needs to be taken out, then placed back in the water to make this work? Some kind of reverse latching thing? I know you guys were great help last time so thanks in advance again!

 

[KMoffett]

tom,

Are you referring to my circuit? https://www.electro-tech-online.com/threads/water-activated-monostable-switch.100583/#post817858 Contacting the water with the two probes should trigger the monostable. After that times out, the 555's output should be low, even with the probes still in the water. Have you added anything to it or are you just looking at the monostable's output.?

Why start a new thread on the same project?

Ken

 

[tom08]

Sorry I started a new thread because it's kind of a different question but i realise i didnt have to. No im not referrring to that circuit in particular, I bought a liquid sensor and have that where a switch would be, no other changes to a normal 555 timing circuit. (pins 6 & 7 connected between a resistor and a capacitor, pin 2 connected between a 10K resistor and the sensor) Just to clarify, i couldnt use yours because i have to design it myself and the changes you made would be obviously not ones i could have come up with!

 

[KMoffett]

I bought a liquid sensor and have that where a switch would be

What switch?

Ken

 

[tom08]

the switch normally on pin 2, so the liquid sensor is one side of pin 2 and a 10k resistor is the other side, the wire from pin 2 goes in between them. fyi, the liquid sensor has some sort of complicated reed switch thing inside that closes when water is present and offers no resistance which is why the thing keeps going.

 

[KMoffett]

You didn't mention the input capacitor in my circuit. That's what makes it a single pulse to trigger the monostable, not a continuous contact. If you're using a continuous closure with you sensor in pin 2, the monostable won't time out.

Just to clarify, i couldn't use yours because i have to design it myself and the changes you made would be obviously not ones i could have come up with!

My guess is that you are not "designing" the circuits you're using, but combining things you found on the web. Even my circuit is not exactly mine. See circuit #5: **broken link removed** All I did is replace the transistor with water probes, and use high resistance and low capacitance components on the input to pin 2 to compensate for the high resistance of water.

Ken