stumped on a 555/556 project.

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dacflyer
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Re: stumped on a 555/556 project.

Post by dacflyer » Fri Jan 15, 2010 8:20 pm

so i am guessing that the cap is charged and holds long enough to keep relay energised.
is that correct ? if so, sounds good, i'd have to try it. on the bench 1st ;)

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Re: stumped on a 555/556 project.

Post by sghioto » Fri Jan 15, 2010 9:07 pm

so i am guessing that the cap is charged and holds long enough to keep relay energised.
is that correct
That's correct. The resistance of the coil along with the drop out voltage of the relay will determine the value of the cap needed.

Steve G.

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Re: stumped on a 555/556 project.

Post by dacflyer » Sat Jan 16, 2010 8:03 pm

gotchya ok,, might also be bennificial to use a ac relay, due to the fact that they have that piece of copper on the coil to help ac relays avoid the chatter .
i'll be playing with it and keep you all updated.

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Re: stumped on a 555/556 project.

Post by sghioto » Sun Jan 17, 2010 7:48 am

I don't think you will have any luck with an AC relay, the coil resistance is too low and they're designed for 60Hz operation. If you don't have a suitable relay you can try this transistor version. Just make sure the transistors used (either discrete or a darlington) will handle the relay coil current. With the component values shown the 50ma relay I used would hold for over 1 second.

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Re: stumped on a 555/556 project.

Post by CeaSaR » Sun Jan 17, 2010 4:26 pm

Wouldn't it be possible to use a transistor switch in line with the power supply for the 555, driven by the
power of the turnsignal being connected to the load? I would think that would be easier/more space saving
than using a relay as suggested.

Just my take on it.

CeaSaR
Hey, what do I know?

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Re: stumped on a 555/556 project.

Post by sghioto » Mon Jan 18, 2010 11:43 am

CeaSaR wrote:
Wouldn't it be possible to use a transistor switch in line with the power supply for the 555
You sure could. I prefer the reed relay option because it will give you a definative ON-OFF response. The relay listed fits in a standard 14 pin dip socket which is fairly small and using just the relay and cap would have less parts obviousy. It's dacflyer's project so I guess he will want to use what ever he already has on hand.

Steve G.

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Re: stumped on a 555/556 project.

Post by dacflyer » Mon Jan 18, 2010 5:34 pm

i just happen to have a card of them reed type relays off of a computer card for some sort of test equipment.. i'll use one of them, thanks guys..

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Re: stumped on a 555/556 project.

Post by dacflyer » Sun Mar 07, 2010 9:20 am

hey all, i finally had time to finish this project, using the cap across the relay to hold a charge works great, 330uF cap worked great, hold relay for almost 1 sec after power is gone. :D
and i am using the ding dong chime from radio shack, that is pleasant sounding.

later i might adjust the timing cap on the 555 circuit, to give it just a little more delay before it triggers the chime..2-4 sec more..
but other than that it works great :D
thanks again....

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