design help

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

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

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' :-)

TTL?

Jim

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

=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|

| =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.

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?

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

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

a PIC.

too.

Bank-switching is evil.

Hope This Helps! Rich

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

Cheers! Rich

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

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

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

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

Parity. ;-)

Cheers! Rich

REAL PROGRAMMERS DON'T USE LOWER CASE.

JOHN

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