On 18.7.2012 1:20, IVP wrote:
>> Put the PIC in, why don't you trust random strangers you met on
>> the internet?
>
> 8-))
>
> I know you're a stranger, but didn't realise you're random too. Do
> you feel particularly quantum ?

Sorry, I don't get it?

> OK, I did put the PIC in and you're right. With loading, the
> voltages do drop to within spec
>
> The pot allows finer resolution at the higher frequencies, although
> it's stable only in the range 2.4MHz - 4.4MHz. Below that, Fosc
> starts 'breaking up'. The 'scope and frequency meter averaging
> shows Fosc does decrease (down to DC) but the waveform is
> jittery and quite irregular, getting progressively worse as Fosc
> decreases
>
> Although it's a side-issue to the project, I'm interested enough to
> delve further. I'll try the other circuit you posted too
>
> Thanks

I know I can't be wrong so I had to try the circuit out myself :)

I was off with the resistor values. The transistor circuit with R1=3D12k,=20
R2=3D1k5 and P1=3D5k works nicely from ~500kHz to ~4MHz and the frequency=20
change looks pretty linear with control voltage 9V-5V on Q1 base .

You can tweak R1 to adjust the maximum frequency and tweak P1/R2 divider=20
to adjust minimum frequency.

I was using PIC12F1822 for testing. Keep in mind that if you go to sleep=20
there will be a ~350uA current flow through the PIC input protection diode.

Djula

>
> Joe
>

--=20
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