Texas12R
Zone Head
Posts: 545
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posted May 02, 2007 12:43 PM
how can you design a simple12v off delay circuit
Is there an easy way to design a 12v circuit that will energize by momentary p/b
and remain on for say 75-100 ms the drop out....
  
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buddy
Expert Class
Posts: 335
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posted May 02, 2007 01:38 PM
 Edited By: buddy on 2 May 2007 15:57
Don't know what this is for or how complicated you want to get. One way would be to use the MPS box from an air shifter. When the button is pushed, adjust the MPS box to stay activated for 75-100 ms. It puts out a Ground, but it could operate a small relay that would stay operated for the time period and forward a battery.
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thekaz
Needs a job
spell chequer is bustimicated
Posts: 2909
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posted May 02, 2007 06:12 PM
bosch makes adjustable timer relays or get ahold of ridgeracer cuase his brain is better than everyone elses
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Texas12R
Zone Head
Posts: 545
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posted May 03, 2007 02:28 AM
I had hoped for a ridgeracer mini-tutorial or something like that  but I do appreciate the replys.......Im just playing around with some ice cube relays I found at work
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ridgeracer
Pro
Posts: 1309
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posted May 03, 2007 09:03 AM
Edited By: ridgeracer on 3 May 2007 10:04
The down and dirty way to have the relay remain on for a short period after you release the button is to simply put an electrolytic capacitor in parallel with the relay coil. When you push the button it energizes the relay and charges the cap. When you release the button the cap discharges into the relay coil keeping it energized until the cap runs out of energy. The larger the capacitance (microfarads or uF) the longer the relay stays on.
Its hard to calculate the size of cap you need with out more info on the relay coil resistance.
BTW putting multiple caps in parallel creates a cap equal to the sum of all the caps. In other words if you place a 220uF cap and a 330uF cap in parallel it acts the same as a 550uF cap.
Be sure your cap is rated for at least 25VDC and that you get the polarity correct. The relay coil doesn't care which end is plus or minus 12v but the capacitor does.
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Texas12R
Zone Head
Posts: 545
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posted May 03, 2007 02:04 PM
Thank You Mr Bially. I will let you know how it turns out.
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