-Not sure if cost is a big factor, but you could use the VCO (voltage
controlled oscillator) section of a standard 74HC4046 - 1 cap plus 2
resistors to set the frequency range and a pot between ground and
VCC to provide the variable `tuning` voltage.  As an added bonus
the output has 50% duty cycle and is CMOS compatible :-)

-James

> Hi list! I have a question. I need a variable-frequency square-wave
> timing signal in the range 3-5MHz. For slower applications, I usually
> wire up a 555 in astable mode with a pot to control the period (and
> maybe another to control the duty cycle, if need be). But I can't
> seem to get the 555 to go fast enough for my current project. I've
> been using a 4MHz crystal oscillator, but now discover I need to
> vary the frequency +/- 1MHz (with 50% duty cycle or so: it isn't
> critical). It would be great to be able to vary the frequency
> continuously with a pot. Any suggestions? Thanks in advance!
>
> Michael V
>
> Thank you for reading my little posting.
>
>
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