UA555 Astable LED Flasher

Application

This circuit shows the UA555 as a free-running astable oscillator driving an LED indicator. It is a common first timing circuit for blinkers, clocks, tone generators, and simple pulse sources.

Design Context

RA and RB charge and discharge the timing capacitor at the THRESH/TRIG node. DISCH pulls the timing network low between cycles, while RESET is tied high so the oscillator can run. The LED branch gives the output a visible load.

Expected Behavior

The timing node ramps between the internal thresholds and the output switches state as the capacitor charges and discharges. If transient convergence is sensitive on a local runtime, use the schematic values as the starting point and shorten the run time or increase the time step before exploring.

Suggested Experiments

• Increase CT to slow the blink rate.
• Change RB to alter the duty cycle.
• Compare Vtiming, Vout, and Iled to see how the timing capacitor controls the LED current.

Featured Component

UA555 is the timer core. Its TRIG, THRESH, DISCH, RESET, CTRL, VCC, GND, and OUT pins are wired in the standard astable timing topology.