I am trying to design a warning sign with several bulbs which a section of the bulbs turn on while the other section just stay off. Then the section that just turned on would turn off and the other section will turn on. Can anyone give some help what to do to get that project finished. Thanks in advance. Ed
use a 555 timer for the duration pulse.. have it drive a DT (double throw relay).. the main power goes the Center pole of the relay. the outer legs will connect to one set of lights. etc...
-- Real Programmers Do things like this. http://webpages.charter.net/jamie_5
first you need to figure out what sort of lights to use.
-- Bye. Jasen
Hi, Ed. If you're using a DPDT relay and you've got a 12VDC supply available (you can always use a wall wart), this may be the easiest way to do this (view in fixed font or M$ Notepad):
| CRY1B | o---o NO | .--o--__ | | o---o NC | | |VCC VCC '----------o C | + + | | NC | | '---o ___ |/ NPN Darlington | __--o-|___|--o---| | .---o C R | |>
| | NO +| | | | C --- | | | --- C| | | | C|RY1 | | | C| | | | | |=== === === |GND GND GND | | (created by AACircuit v1.28.6 beta 04/19/05
Look for a 12VDC relay with a 400mW coil. You can use just about any NPN darlington in a TO-220 package. With a 1000uF cap and a 1K resistor for R, you should have a total cycle time of around a second.
The idea behind this circuit starts with the fact that a 12V relay will typically turn on at about 9V or so. Once it's on, the voltage across the coil typically has to drop to about 4V for the relay to open up.
When power is applied, the cap is at 0V, so the relay will be off. The normally closed (NC) contact starts charging cap C up to about 10.4V, which will put about 9V at the coil, turning the relay on. The contact changes over, and the resistor R is then connected to GND, discharging the resistor until the cap voltage gets down to about 5.4V, which means there's less than 4V across the coil. This makes the relay turn off, which repeats the process.
Hook up your lights to the N.O. and N.C. contacts of the other pole of the relay.
There are a couple of limitations to this circuit. First, the duty cycle (% time on) is pretty much fixed at a little less than 50% (it takes a little longer to charge up than discharge, because the base of the darlington is stealing a little current from the cap). You can provide some control over total cycle time over a limited range by putting a pot (say, 2K to 5K) in series with the R. This will give you up to several seconds cycle time. Timing on this circuit is susceptible to change with mechanical vibration. Also, this circuit won't work very well at lower voltages (although it will work well at
24VDC).If this doesn't do it, possibly you could provide a little more information (like what voltages you have to work with, what kind of timing cycle you want, and what kind of precision you need in your cycle time).
Good luck Chris
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