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Active time of a relay

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rudolph.vermaak

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I am building a circuit containing a digital reciever 12VDC (make: Sentry 3CH RX). This reciever must drive a independant relay which controls a 110VAC motor inturn this motor controls a light which moves up and down. Two of the reciever's channels is the control for the up-down function, now the problem is that I cannot get the relay to stay on for a shorter time. By that I meen that the reciever would send a pulse of 1 second to the relay, the relay would switch and the motor would move, but I dont want the motor to move for 1 second I want it to move for exactly the time I press the transmitter's button. Is there any way of controling this relay by the use of a IC or some other method and getting it to cut the time by atleast 2/3 rds :?: [/list]
 

Klaus

New Member
Let me see if I got your question right: you want to activate a relay for periods shorter than one second even though the relay itself is activated by a 1 second long pulse from the receiver?
You could do this by the receiver triggering a one shot multivibrator, the pulse output of which is adjusted to the duration you want. You need a retriggerable one shot, I think the 4528 chip is a dual retriggerable one shot, so it resets itself for the next trigger input once the one shot pulse had expired.
You still need to wait at least one second before the next pulse from the receiver can repeat the cycle.
Of course, the chip output cannot drive a relay direct, you need at least a transistor driver (and a reversed diode across the relay coil for EMF suppression).

There is a limit for how short a relay can reliably stay on, someting to do with the mechanical inertia of the design. For real short on times you'd need an electronic switch but by then you run into the inertia problems of the motor itself.
Good luck with that one,
Klaus
 

Phasor

Member
Sounds to me like you have the wrong motor for the job. You should be using a stepper motor, which provides more precise positioning control. And if you use a stepper motor, you would not need a relay. It can be driven directly from a stepper motor driver IC.
 
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