relay oscillator

[chicoteld]

I remember seeing a circuit for cross connecting two relays through a capacitor that created a very simple oscillator which repeatedly turned one relay on and then alternately the other one as long as power was applied. It had about a 1Hz frequency. The resistance in the relay coil and the capacitor formed an RC delay factor. Has anyone else seen this circuit and can share it with me? Thanks.

[philba]

it would be fairly easy to work out a circuit to do this but why would you want to? Most relays are rated for like 100K to 1M operations. When there are 86.4K seconds in a day, they wont last very long.

[ian]

B]but why would you want to? Most relays are rated for like 100K to 1M operations. When there are 86.4K seconds in a day, they wont last very long. [/B]<p> Phil.......what a sad life you must live....
Haven't you ever bet on something you're sure to lose? Don't you ever approach a chic that'll surely reject you? Have you never reversed the polarity of an electrolytic just to see it explode? I say pulse that relay, pulse it baby!
Ian

[Mike6158]

Sounds like Phil and I should both be bummed out... Maybe later...

[Chris Smith]

Ive built many of them. You only need one relay to make it flip on and off. Has to be a two pole type. However using just one chatters quite fast, the second one allows you to pass a current into a large cap, and this cap keeps the relay on for the caps size time value, while the second relay contacts drops and charges another cap and [2]relay on, the first runs dry and colapses which then feeds the other and so on. Its not very complex. Using two scrs and smaller caps with Leds as a bleed, also works the same way. Same with the two transistor osc.

[philba]

You can pulse the relay all you want - it wont change anything. Relays are mechanical beasts. The metal they use fatigues with flexing. In addition, under heavy loads the contacts will arc and pit. Eventually, they will fail to make a connection. Try reading some specifications. <p>While you are at it, why don't you try reading up on civility.<p>Phil

[Enzo]

Sometimes we want to do something just to see that it works, even if it is not maybe so practical. I call it a proof of concept design. Maybe a couple chips would do the job better, but we never learn about the relays then.<p>Wire the coil from a relay through one of its own normally closed contacts, and you have an instant buzzer. Not very practical or long lived, but it verifies a bit of relay logic if you were not sure to begin with.<p>SOmetimes we just want to learn something. Remember, that probe we sent into Jupiter had no landing gear.<p>
(No I am not confusing Cassini/Huygens)

[Bernius1]

Amen. And when you find a way to flash your outdoor Christmas lights all winter, only at night, not in the rain, and at a rate proportional to humidity, all from junk under your bench ? You say 'see, honey, it wasn't junk after all'.
I wanted once to take a blow-molded plastic cat with a pop-out head, and install a thermometer spring. Put it in Grandma's garden, and when the cat looks left, it's 20-degrees, and when right, it's 80 , with the scale on the collar. $8.99
Somebody wake me.<p>BTW*** I know ALT-148 is the 'degree' mark in ASCII in some fonts. Can we get the ASCII ALT-numbers for 'degree' 'squared (2)' 'cubed (3)', 'approx-equal', 'not equal', etc.? Like a mathematics font to support the posts.

[philba]

So I guess your point is I shouldn't post responses like "you'll break it" or "that might kill you" as it will disuade some one from doing it? We should only have positive posts here? <p>Me, I like building stuff that won't fail. I'm not against pushing limits or learning about stuff but I don't mind information either. I'd rather know if something is going to break, even if I go ahead and do it. <p>Consider the other side, suppose some one builds something and installs it only to discover it failing fairly soon. Do you think they would have wanted to hear a cautionary voice? Guess I'd feel bad if I sat silently by.<p>Finally, if you have ms word, you can go to insert/symbol to find the different fonts and see what is available like - √ (you should see square root). Several fonts that have those symbols. Be aware that the reader's system needs to have the font installed and non-windows readers may not see your symbols. (third edit on this one - I was testing the symbols)<p>phil<p>[ January 21, 2005: Message edited by: philba ]<p>[ January 21, 2005: Message edited by: philba ]<p>[ January 21, 2005: Message edited by: philba ]</p>

[chicoteld]

Sorry I caused such a stink. For the record, this is a quick and dirty solution that only needs to work for 5 minutes on 5 consecutive nights and then I can throw it away. That's part of the reason I didn't want to go the entire 9 yards with chips, SCRs, pc boards, etc. I have relays in the junk box, so I figured I didn't need to over-engineer an elegant solution.

[Carl Pugh]

Chic, in my opinion, your question is totally acceptable.<p>If you have a function generator, you could set it to 1 hertz and drive relay with it.

[Chris Smith]

It’s a great lesson in Logic, and RC constants.
Like Nike says, Just do It!

[terri]

Apropos of slow relay actuation:<p>Anybody know if wrapping a sheet of copper around the relay coil would slow it down? (Sort of a short-circuited low-z secondary.)<p>Back when dirt was new, I used to use delay relays that had a slug of copper on one end of the coil to delay the relay's operations. I wonder if it would work the same with a sheet of copper around the coil in this instance?<p>So? Yes? No?<p>Anyone know offhand?

[Enzo]

In older Rockola Juke Boxes there was a relay in the credit unit called the delay relay, and it had an elongated pole piece with brass washers on it, and it took longer to pull, or release or something. It was made that way for timing in a complex relay logic system.<p>Philba, keep on warning that this will kill you, and if something won't work, by golly say so. What comes to my mind though, is to answer someone's question, then explain why it is a bad idea - like it will burn up after ten cycles. And certainly offer better ways if we know what the original intent was. But always answer the original question because it might have been asked to understand something. "Here is how you would do it, and here is why you shouldn't."<p>One of my personal beefs is the "use a PIC for it" response to requests for logic circuits. No one learns how logic works that way. As a practical solution to a problem, or for a commercial product, the PIC might be better, but if one is trying to glean some knowledge of TTL, then it is no help.<p>ANd Ian, I do also think that the sad life comment was rude at best. There is no need to be uncivil here.

[k7elp60]

I think you want a flasher. I will describe the connections and give you two options. One is a flasher the other one is a delay on with only one relay. Having a large quantity of parts I built and tested this circuit. I used a Omron G5LE-114P-PS relay. It has a 12VDC coil and measures about 360 ohms of resistance. It has SPDT contacts
Connect a 3300uF electrolytic capacitor directly across the coil. Connect the - lead of 12VDC to the junction of the coil and the - lead of the capacitor. Connect the + lead of the 12VDC to the wiper of the relay. Connect one lead of a 150 ohm resistor to the NC contact. Connect the other lead to the junction of the relay coil and the + of the capacitor. A load connected to the NO contact and the - lead of the 12VDC supply and you have a flasher.
If you connect the resistor lead connected to the NC contact of the relay to the + lead of the 12VDC you will have a delay on operate relay. The time delay is about 2 seconds with the values listed. Dropping the resistor to 75 ohms makes the time about a second.