digital "pots" have been around for quite a while...

[Phil]

I'm quite impressed that the capacitance goes that low. Making a five-bit digitally-switched capacitor with standard 4000-series CMOS is fairly straightforward, but obviously you are limited by the stray capacitances present. The Arduino-based crystal set is still on the cards!

Phil M1GWZ




On 20 Mar 2012, at 11:44, Robert E. Seastrom wrote:

> 
> I was disappointed they only go up to 5.5pF.  Nowhere near enough to
> build myself an Arduino-driven crystal set.
> 
> -r
> 
> Mike O'Dell <mo at ccr.org> writes:
> 
>> I see - "Sparkgap Defined Radio"
>> 
>>    -mo
>> 
>> 
>> On 3/19/12 10:55 PM, Joseph Bento wrote:
>>> Now if they can make them with the equivalent of 3,000 volt spacing on the plates...
>>> 
>>> Joe, N6DGY
>>> 
>>> On Mar 19, 2012, at 8:53 PM, Mike O'Dell wrote:
>>> 
>>>> this was, i guess, inevitable?  digitally adjustable capacitors
>>>> 
>>>> 
>>>> http://www.psemi.com/content/products/apps/product_dtc.html
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