555 Astable Multivibrator

Mixed-signal

The timing capacitor integrates between $\tfrac{1}{3}V_{cc}$ and $\tfrac{2}{3}V_{cc}$ . The timing-branch stroke weight scales with instantaneous $V_C$ , and the LED node flashes in sync with the calculated frequency (time-scaled for visibility).

Live circuit astable, 5.76 Hz, 60 % duty

Drag a value tag to change that part. Click a wire to clip a probe on.

Causal signal trace paused

Bias the timing ladder $V_{CC}$ drives RA and the timing network.

t_{\mathrm{stage}}=\htmlData{math-slot=value}{\mathtt{0.00}}\,\mathrm{s}

Step 1 / 4 Bias the timing ladder

Notebook: 8 parts and 10 wires, modelled as hybrid charge/discharge integrator

Recommended lab 4 of 18

Relate RC charge thresholds to oscillator frequency and duty cycle.

Builds on: Dynamic RC Low-Pass Filter

Predict, then test

Increase $R_B$ while $R_A$ and $C$ stay fixed. What changes first?

Commit before the explanation appears. This is a prediction, not a quiz score.

Governing model

f = \dfrac{1.44}{(R_A + 2R_B)\,C} \;\cdot\; D = \dfrac{R_A + R_B}{R_A + 2R_B}

Parts

8-pin 555 IC block
$R_A + R_B$ timing pair
timing capacitor $C_T$
output LED + limiter

Limits of the model

$V_{cc}=5\ \mathrm V$
threshold $\tfrac{2}{3}$ · trigger $\tfrac{1}{3}$
astable + monostable modes

Diagnosis challenge The fault is hidden. Work it out from the changed outputs first.

Notebook: 8 parts and 10 wires, modelled as hybrid charge/discharge integrator

Increase RBR_BRB​ while RAR_ARA​ and CCC stay fixed. What changes first?

Increase $R_B$ while $R_A$ and $C$ stay fixed. What changes first?