hi,

if I have a constant drip of water and i want to know exactly when each drop falls, so you can say the water is like a resistor and put two wires aligned exactly below the drop and when it falls it will trigger a 741 op amp circuit to make a line go high to 5V, so it can be detected by a PIC microprocessor.

so i have this sketch and its kinde works but not so good i wanted to know some advice about how to approach this to get it to work better, meaning what changes can be done in the circuit to adjust it to work better.

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hi,
I would suggest is to use a CA3140 CMOS opa, they have a very input impedance, the 741 is a dinosaur.

Do you have a picture of the system you could post?

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Eric
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hi atntias,

will the water drop get the electrodes wet or just pass between them?

 

Yeah if they get wet then remember to use something like graphite (?) I believe because it won't oxidize.

 

yes the water drops do touch the contact and it covered with gold so it wont rust, the thing is i am getting some changes in the voltage but not good enough to be detected by a PIC. any ideas?
other methods are acceptable to the goal is to know the drop rate with good precision.

here are some pictures of the system...

Attached Images

	DSC06090.JPG (147.7 KB, 38 views)
	DSC06092.JPG (145.0 KB, 24 views)
	DSC06089.JPG (141.2 KB, 20 views)

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What opamp did you use?.

Also I would suggest using it as a comparator, rather than this rather crude way.

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Yes, I would also suggest using a comparator (or an op-amp as a comparator). You want a logic-level output, and comparators are good for that.

 

well i asked this quesion at another forum (dutchforce) and Søren came up with this solution which gives a ~10µs pulse out when the drop ceases to bridge the input.

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Here's one that puts out a logic HIGH as long as water bridges the gap.

Attached Images

water droplet dtector.PNG (21.5 KB, 38 views)

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Ron

 

[quote=atntias]hi,

if I have a constant drip of water and i want to know exactly when each drop falls, so you can say the water is like a resistor and put two wires aligned exactly below the drop and when it falls it will trigger a 741 op amp circuit to make a line go high to 5V, so it can be detected by a PIC microprocessor.

so i have this sketch and its kinde works but not so good i wanted to know some advice about how to approach this to get it to work better, meaning what changes can be done in the circuit to adjust it to work better.

QUOTE] [snip]

How about just using a waterproof microphone? And amplify the sound it makes when the drop hits. Or put a regular mic. inside a small waterproof drum.

 

that would be allot more complected because the drip is fast and ul have to deal with noise reduction and voice analysis the 2 solutions above provide a much more accurate and simple solution.

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I can understand your outright rejection of my suggestion if you think that it is necessary to apply "noise reduction and voice analysis" to the mic. output. (I think the s/n ratio will take care of that)
And I might even understand why you don't think the mic. would not respond to a "fast" drip in an "accurate" manner. (limited frequency response?)
But I do understand that you probably never have heard a mic. being hit by a raindrop (or anything else) and checked the signal on an oscilloscope.
And now i understand why you posted the in the first place.

 

hi,
Rolf is quiet correct about the sound amplitude of a water drop hitting a mike.
If you choose your mike carefully, you will require minimal amplification.

I have used low cost mike's as impact detectors in rolling mills.

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Eric
"Good enough is Perfect"

PIC tutorials:
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Bill's: www.blueroomelectronics.com/

 

i understand that if the water is hitting something hard and making a solid noise then is possible.
but that not the case the water is dropping to a container filled with water and there are splashes that make noise too, the drop rate is quite fast so u will have to analysis the voice and find wich peak is the water drop and what are the splashes it just seems to me much more complected... if u have an idea to simplfy it i will love to hear it im not denying any ideas as it may seem.....

just to note what are the requirements, the water is dropping to a small container willed with about 2 inches of water which an overflow hole to where the pump is... i can place a mic in the container walls but the affect of the drop hitting the water is important...
if u have any other question don't be shy

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Don't quite understand what you are doing, thought you were counting drops.
I would think a water drop hitting the mic. or a membrane close to it is going to make the mic. output many times bigger than any acoustical noise from splashing of droplets hitting the water or the sides of the container.
Did some crude checks on droplet rates, anything over 5 or 6 per second tends to make the water go in broken streams. Don't think you can get much more than that even under ideal conditions.