Oscillator Circuit Trials ...

• Basic (2-R) 555 circuit:
  
  • Accuracy of output freq calculated from formula on osc page
    was poor, even with precision resistors, though unknown tolerance of caps could explain most of it...

• VCO:
  • Starting from Basic-2R circuit above,
    with R₁ = 68k, R₂ = 15k, C₁ = 10uf,
    calculated freq s/b 1.0 Hz
    Actual freq 2.1 Hz (scope measured)
    • With a 5k pot, between gnd and +V,
      wiper connected to pin 5 (.01 cap removed)
      freq variable from 0.7 Hz (pin 5 at +V) to 1.5 Hz (pin 5 near gnd)
  • with R₁ = 2700, R₂ = 15000, C = 0.47uf,
    calculated freq s/b 94 Hz
    Actual freq 99 Hz (scope measured)
    • With a 5k pot, between gnd and +V,
      wiper connected to pin 5 (.01 cap removed)
      freq variable from 33 Hz (pin 5 at +V) to 122 Hz (pin 5 near gnd)

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• Basic (1-R) 555 circuit:
  
  • Accuracy ...

eof