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Astable multivibrator circuit (555 or BJT)

Short answer

Using a 555 timer, RA from VCC to pin 7, RB between pin 7 and pins 2/6, capacitor from those pins to ground. Output frequency f = 1.44/[(RA+2RB)C]. A BJT astable uses cross-coupled RC pairs with frequency f = 1/(0.693(R1C1+R2C2)).

Draw AMV circuit using IC 555 or BJT.

Astable multivibrator using IC 555

              +VCC
               |
       +-------+---------+
       |       |         |
     [RA]     (8) VCC   (4) RESET
       |
       +----------------(7) DISCHARGE
       |
     [RB]
       |
       +-------+--------(6) THRESHOLD
       |       |
      [C]      +--------(2) TRIGGER
       |
      GND               (3) OUTPUT ---> square wave
                        (5) CONTROL --[0.01 µF]-- GND
                        (1) GND
  • Pin 8 (VCC) and pin 4 (reset) go to +VCC; pin 1 goes to ground.
  • RA connects VCC to pin 7; RB connects pin 7 to the capacitor node; pins 2 and 6 are joined to the capacitor.
  • Pin 5 is bypassed to ground with 0.01 µF.

Output: f = 1.44/[(RA + 2RB)C], duty cycle D = (RA + RB)/(RA + 2RB).

Astable multivibrator using BJTs

        +VCC
   +-----+--------+--------+
   |     |        |        |
 [RC1]  [R1]     [R2]    [RC2]
   |     |        |        |
   +--C1-+---B2   B1---C2---+
   |                       |
   Q1, Q2: NPN, emitters to GND

Connections: the collector of Q1 is joined through C1 to the base of Q2; the collector of Q2 is joined through C2 to the base of Q1. R1 connects VCC to the base of Q2, and R2 connects VCC to the base of Q1; the emitters are grounded. The output is taken from a collector. f = 1/(0.693 (R1C1 + R2C2)).

✓ Answer checked by Claude Opus 5.5 (high effort)

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