Need help to extend capabilities of a simple proximity circuit

Retriggerable monostable.

Cheers

The pressure pad idea seems good, how do you have that setup ?

--
Cheers ............. Rheilly

The sensor probably puts out a voltage level which depends on proximity. That voltage level is tested by a 'comparator' circuit to see if it is high enough. If it is, it turns on the output. The voltage at which it decides to turn on the output is a switching point.

The problem is that the output is not steady, but has a certain low-level noise. As the dog is getting closer, the noise causes the thing to trigger on and off until the dog is close enough so the noise + signal is no longer below the switching point.

The way this is typically handled is to use some positive feedback from the output to change where the switching point is.

Say the thing switches at 6V normally. If you put in some positive feedback from the output, once it switches on, the switching point will go down to, say, 5V. If the noise is less than a volt, it will stay on and not chatter.

If the dog is satisfied, and is leaving, the voltage will begin to decrease, but the water won't go off until the output + noise gets down to 5V. At that time, however, with the positive feedback, the switching voltage will be modified to 7V, so it won't chatter. Now, when he returns to get more water, it won't switch until the voltage gets to 7V.

In order to determine how to do this, you need to post the circuit you built, so I can see where to put the extra resistor.

The other problem you might be encountering is that the relay coil takes a certain amount of current to switch the relay on. If your sensor is measuring a voltage, it might be affected when the coil turns on and off. Does the mad switching occur when the relay is not hooked up? If not, then you can try putting a big electrolytic capacitor (like the ones they use in power supplies), like 3300uF, across the sensor power inputs, to protect it from dips when the relay turns on.

You can also run into this problem with a 555, which can end up either not turning on, or staying on and not shutting off, due to the change in the 12V input.

Fun project.

Regards, Bob Monsen

Good explanation Bob. Let me add a couple of synonyms for the 'little bit of positive feedback on the comparator' to also search for... hysteresis and schmidt trigger

Some friends of mine have used one of these for years for their dogs. Just attach it to the faucet. No electronics, etc.

Hi,

Thanks for all the great feedback. Anybody know how I can add an image to this thread. I would like to show you the current working circuit, for the sake of this thread.

I did google the schmidt trigger, and this looks as though it should fix the problem. Found it here if anybody else is interested:

Near the end of the page.

The reason I am ditching my pressure pad idea is it was a home made switch that doesn't take kindly to water. Hence, when the dog drinks it is splashed with water.

So far the proximity sensor is a good idea, just need to fix the bouncing problem with the relay. Hopefully the schmidt trigger will overcome this small and annoying problem.

Many thanks,

Chris

First, you should recognize that this is NOT "Google Groups".

*-a-service-for-*-*-*+Usenet+*-Wikipedia+hide.the.fact+*-*-policed+concerns-*-*-*-*-about-the-Google-interface+*-*-follow-Usenet-customs-and-*-rules+*-*-*-not-*-mustered-*-*-*-*-*-*-*-*-*-*-*-*-*+*-*-*-*-*-*-*-software+less-*-savvy-*+*-*-*-*-*-*-*-*-*-*-*-*-is-now-legendary+zzz+*-summary+qq+Web

Second, you should discover the *types* of Usenet groups and the differences between those.

*-*-post-graphics-*-*-*-*+*-*-*-*-*-*-*-alt.binaries-hierarchy+enforced-by-filtering-*-*-*-*-*+never.see.it+Retention.times+text.groups+qq+*-*-*-binary-*-posts+*-get-rejected-*-*-*-*-*-*+*-*-get-dropped-*-*-*-*-*-*-*-*-*+set-up-a-*-site

You're on the right track--but graphics are quickly lost to posterity. The persistance of ASCII schematics on Usenet is excellent.

Note the date.

It is possible to do amazing stuff with just ASCII.

If you can't be convinced to do it with ASCII, Mark Zenier's FAQ post (link above) mentions the *binaries* group that is associated with this hierarchy. (I think this should be listed UNDER the item below, but many will disagree with me.)

There are other obvious ways to share images.

*-*-*-*-*-personal-webspace

Among those, The Pirate Bay's offering is the least offensive IMO.

If Monsen had spelled it properly, you would have gotten even more hits.

...and since it's named after a guy, it's always capitalized.

no fair, I didn't mention the guy... ;)

Regards, Bob Monsen

JeffM wrote:

Bob M>no fair, I didn't mention the guy... ;)

After this recent effort news:ihROj.4567$ snipped-for-privacy@newssvr21.news.prodigy.net

you get special dispensation from me on all counts. 8-)

Note to the OP: That is *another* example of the utility of ASCII art.

Greetings Chris..

Regarding: "I am attempting to build a device that will allow my dog to turn on an outside tap to allow him to drink straight out of the hose. This way he always has fresh water whenever he needs it. "

I fully realize that this may be a learning endeavor/exercise. And you're just wanting to see if you can develop something out of ordinary items around the house. But DO be aware that you're probably re-inventing the wheel here, there's a few veterinarians that got the idea some time ago:

Consider..

Inside or out:

Go to,

Search on, automatic pet drinking fountain Click on Google Search

Notice that the commercially manufactured units have custom plastic moldings/housings, hoses and overall designs to make them easy to use and place. Just something to consider..

Cheers, Mr. Mentor