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timed relay?Printed From: the12volt.comForum Name: Relays Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc. URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=81263 Printed Date: July 03, 2025 at 2:11 PM Topic: timed relay? Posted By: zee4speed Subject: timed relay? Date Posted: August 06, 2006 at 9:27 AM I need a timed relay for misc. purposes. I know I can use a 528T. But I was wondering if there are any other alternatives.
Replies: Posted By: josh1979 Date Posted: August 06, 2006 at 10:53 AM here the only other way i know ------------- bring back the rotary phone so i dont have to press 1 to proceed in english Posted By: zee4speed Date Posted: August 07, 2006 at 12:16 AM Josh thanks soo much for all your help. Posted By: josh1979 Date Posted: August 07, 2006 at 7:25 PM Creating a Pulse
The way the 555 timer works is that when you flip the first switch, the Output pin goes to Vcc (the positive power supply voltage) and starts charging the capacitor. When the capacitor voltage gets to 2/3 Vcc (that is Vcc * 2/3) the second switch turns on which makes the output go to 0 volts. The pinout for the 555 timer is shown below
Pin 6 is the off switch for the pulse. We connect the positive side of the capacitor to this pin and the negative side of the capacitor to ground. When Pin 2 (Trigger) is at Vcc, the 555 holds Pin 7 at 0 volts (Note the inverted voltage). When Pin 2 goes to 0 volts, the 555 stops holding Pin 7 at 0 volts. Then the capacitor starts charging. The capacitor is charged through a resistor connected to Vcc. The current starts flowing into the capacitor, and the voltage in the capacitor starts to increase. Pin 3 is the output (where the actual pulse comes out). The voltage on this pin starts at 0 volts. When 0 volts is applied to the trigger (Pin 2), the 555 puts out Vcc on Pin 3 and holds it at Vcc until Pin 6 reaches 2/3 of Vcc (that is Vcc * 2/3). Then the 555 pulls the voltage at Pin 3 to ground and you have created a pulse. (Again notice the inverting action.) The voltage on Pin 7 is also pulled to ground, connecting the capacitor to ground and discharging it. To see the pulse we will use an LED connected to the 555 output, Pin 3. When the output is 0 volts the LED will be off. When the output is Vcc the LED will be on. Building the Circuit
Before you start building the circuit, use jumper wires to connect the red and blue power rows to the red and blue power rows on the other side of the board. Then you will be able to easily reach Vcc and Ground lines from both sides of the board. (If the wires are too short, use two wires joined together in a row of holes for the positive power (Vcc) and two wires joined together in a different row of holes for the ground.) Connect Pin 1 to ground. Now connect the power. The LED will come on and stay on for about 2 seconds. Remove the wire connected to Pin 2 from Vcc. You should be able to trigger the 555 again by touching the wire connected to pin 2 with your finger or by connecting it to ground and removing it. (It should be about a 2 second pulse.) To trigger the 555 again, we connect Pin 6 to the trigger (Pin 2). As the capacitor is discharging, the voltage in the capacitor gets lower and lower. When it gets down to 1/3 Vcc this triggers Pin 2 causing Pin 3 to go to Vcc and the LED to come on. The 555 disconnects Pin 7 from ground, and the capacitor starts to charge up again through RA and RB. To build this circuit from the previous circuit, do the following. Disconnect the power. Now reconnect the power and the LED should flash forever (as long as you pay your electricity bill). Experiment with different resistor values of RA and RB to see how it changes the length of time that the LED flashes. (You are changing the amount of time that it takes for the Capacitor to charge and discharge.) Formulas
t1 = charge time (how long the LED is on) = 0.693 * (RA + RB) * C t1 and t2 are the time in seconds. C is the capacitor value in Farads. 220uF = 0.000220 F. So for our circuit we have: t1 = 0.693 * (10000 + 2200) * 0.000220 = 1.86 seconds t2 = 0.693 * 2200 * 0.000220 = 0.335 seconds T = 1.86 + 0.335 = 2.195 seconds Frequency = 0.456 (cycles per second) ------------- bring back the rotary phone so i dont have to press 1 to proceed in english Posted By: hotwaterwizard Date Posted: August 31, 2006 at 9:53 PM
These are Simple Delayed OFF Timers. When you push the switch the timer begins and turns on the relay. At the end of the time the relay switches off. If you push the button durring the timing cycle the timer resets and starts the timing cycle from the beginning. almost any Transistor will work for this circuit as long as it can handle the relay coil load. ------------- John DeRosa (Hotwaterwizard) Stockton California When in doubt, try it out ! |
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