Activating a relay from pulses (from a monostable, for example) can be useful in many types of controls. In the figure we give a configuration that we often use in our projects for its functionality and simplicity. With each pulse produced by the 555 that is obtained from an input sensor, the flip-flop changes state and, consequently, the relay as well. The monostable output pulse duration time (555) is calculated to prevent sensor activation for more than one instant by producing multiple output pulses and thereby erratic circuit activation.
