555 timers, who needs them?

Fig 2

Fig 2 Driving a loudspeaker from a 40106 astable

Fig 3 shows a controlled astable to produce a train of pulses which can be stopped or started by a ‘control’ input. The astable runs when the control input is made high.  It is disabled when the control input is made low.  Note: If you want to drive an LED you should buffer it with a spare inverter and use a low current LED (fig 4).  Otherwise the astable may not function and the LED will stay partially lit when the astable is disabled.

Fig 3

Fig 3 Controlled 40106 astable


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