design help

jamesgangnc · 2009-02-24T13:17:20+00:00

I'm ok with fixing and adapting circuits but not so good with design. I've come up with an electronic switch circuit but I think it could use improvement. The goal is to turn on a 12v relay with a switch that is closed when off and open when on. The switch also has to have one leg grounded. It's a pressure switch with a single terminal. I also want the relay to stay closed (on) for a couple minutes when the switch goes from on (open) to off (closed). Here's what I've got now and it does work. But I had to use a pretty big capacitor and I'm still only getting about a minute of delay when going to the off state. Because I can't make the 10k resistor any bigger. I'm thinking that it is likely possible to get a longer delay and do it with a smaller capacitor if I was better at designing this. The other flaw is that this slowly lowers the voltage to the relay until it drops. The relay stays pulled to about 3 to 4 volts. I also suspect there is a better way to keep it fully on until the rc timer expires. Thanks in advance for any suggestions :-)

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bw 17 years ago

One transistor was my first thought. So simple that there must be countless links. Google time delay relay 2n2222 or somthing like that. A 1 Meg resistor and 1uF cap has a time period of 1 second

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Jon Kirwan 17 years ago

I took a careful look at the OP's situation and didn't "see" a one-BJT solution that provided clean, sharp relay drive on and off.

I'd probably learn something from you here.

I like the solution I have in mind, already.

Yes, I can multiply, too.

Jon

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Jan Panteltje 17 years ago

On a sunny day (Tue, 24 Feb 2009 13:56:04 -0600) it happened krw wrote in :

I recently gave a link to a PIC that says: 'Hello I am mister Ed' :-)

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RST Engineering (jw) 17 years ago

TTL?

Jim

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Greg Neill 17 years ago

Hmm. Is the trigger voltage going to make it below 1/3 V?

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John Fields 17 years ago

I think so. Why not? JF

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jamesgangnc 17 years ago

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0+-----+

=A0 =A0 =A0 =A0|K =A0 =A0|

=A0 =A0 =A0 =A0 =A0| =A0 =A0 |

=A0 =A0 =A0 +-----+

=A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 |

=A0 =A0 | =A0 =A0|A =A0 =A0 =A0|

8] =A0 |

| =A0 =A0| =A0 =A0 =A0 |

| =A0 [1k] =A0 =A0 |

=A0| =A0 =A0| =A0 =A0 =A0 C

=A0 =A0+-----B 2N2222

=A0 =A0 =A0 | =A0 =A0 =A0 E

| =A0 =A0 =A0 =A0| =A0 =A0 =A0 |

=A0 |

=A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

Wired up your suggested circuit but it didn't work. Guess i'm going to have to take the time to figure out how it should work :-) I'll double check my connections first.

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Greg Neill 17 years ago

When the switch is open (and things settle down), the L.H.S. of the trigger capacitor will be just a couple of diode drops above ground (the 1N4148 and the BE junction of the 2N2222). Call it 1.4V. The R.H.S. of the cap will be up at +V thanks to the 100K pullup resistor.

When the switch closes again, the L.H.S. of the cap is forced to ground, an excursion of only about 1.4 volts. The R.H.S. follows, so the trigger pulse is only 1.4V below +V. So unless the +V is less than about 4.2V, the 555 won't trigger.

Or have I missed something obvious?

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Rich Grise 17 years ago

Plus $100.00 development kit, and 6 months to learn to program the damn thing.

Didn't we have a rule here - "No PIC suggestions without full schematic and source code listing and uploadable object code included" ? ;-)

Cheers! Rich

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John Fields 17 years ago

No, you nailed it! Thanks. JF

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Rich Grise 17 years ago

soltion.

I didn't see anything like "more of the same". John's circuit is kick-ass, can be assembled in minutes (OK, maybe 300 or 400 of them ;-) ), and doesn't need any programming skills or $100.00 development kit.

I just wish John wasn't so foul-mouthed.

Thanks, Rich

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Rich Grise 17 years ago

a PIC.

too.

Bank-switching is evil.

Hope This Helps! Rich

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Rich Grise 17 years ago

Precisely my position on the point, plus the fact that bank switching is evil. ;-)

Cheers! Rich

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Rich Grise 17 years ago

So, are you saying that "a voltage regulator, a PIC, a development system, a programmer, and a couple of days (weeks?) learning the instruction set and programming procedures is [more practical] than

5 cheap parts assembled in half an hour"?

You've got a weird sense of priorities, dude.

If you don't want to spend $100.00 for a train or $500.00 for a plane, then, yes, a bike is more practical.

We weren't all born with silver spoons up our ass.

Thanks, Rich

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Spehro Pefhany 17 years ago

Just like the "employees must wash hands" rule, it may be honored more in the breach than the observance.

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Rich Grise 17 years ago

Assembly has ALWAYS been written in upper case! Well, sometimes you can comment in lower case for readability, but lower case code is kinda airy-fairy. ;-)

Cheers! Rich

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Rich Grise 17 years ago

Parity. ;-)

Cheers! Rich

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John Larkin 17 years ago

REAL PROGRAMMERS DON'T USE LOWER CASE.

JOHN

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krw 17 years ago

Nonsense. Mixed case improves readability immensly. Case sensitivity is evil.

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petrus bitbyter 17 years ago

"PIC Hammer" schreef in bericht news:go1bbk$ot0$ snipped-for-privacy@aioe.org...

Hmm... He who can handle only a hammer, considers every problem to be a nail :)

You left out the most important part: The program.

It was mentioned before: "If you offer a PIC-solution then provide the program as well."

*I* would use a 10F200 for a fixed timer and a 10F222 for a variable one. The OP however has neither electronics design - nor programming skills. Even if you provided a program I doubt he could get it into the chip. One still needs a programmer and the know-how to handle it.

A 555 would be my second choice but I also could make something using discretes. If you consider yourself to be a designer, you'll need to have more then one tool in your box.

petrus bitbyter

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