555 timers, who needs them?
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.
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