LM555 as variable frequency oscillator

xyz9915 · 16th June 2009, 06:18 AM

Hello!
I need a circuit in which the frequency of LM555 astable multivibrator can be controlled externally I mean by the help of transistor etc. So, please guide what modification may be done in the attached circuit

bwaslo · 17th June 2009, 01:10 PM

Look into replacing resistors with something like MCP4012.

If you want voltage control, don't use a 555, use a CD4046/74HC4046, a better chip for a variable oscillator, anyway. Use 555 only if you need to vary duty cycle. For most audio uses you'll want 50% duty cycle and something like the 4046 is more appropriate and has more versatile control.

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17th June 2009, 01:10 PM	#2
bwaslo diyAudio Member Join Date: May 2006	Look into replacing resistors with something like MCP4012. If you want voltage control, don't use a 555, use a CD4046/74HC4046, a better chip for a variable oscillator, anyway. Use 555 only if you need to vary duty cycle. For most audio uses you'll want 50% duty cycle and something like the 4046 is more appropriate and has more versatile control.

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