> It's not the same as a purely digital example but I once designed a board=
 that used a direct
>  digital synthesizer (DDS) to generate the reference for a PLL in a micro=
wave synthesizer.=20
....
>
>> I saw one instance of a product in production using an Atmel AVR,=20
>> where there is a single pin which is an ADC AREF input only rather=20
>> than a fully implemented I/O pin.
....

These two stories remind me of a story that appeared in Electronics Austral=
ia "Serviceman who tells" feature. This was a column written by someone who=
se identity was concealed by the editor, but ran a typical one man radio/TV=
 service business in a suburb of Sydney, Australia. This particular story w=
as related to him by another serviceman who ran a similar business in an ar=
ea that had a number of residential tower blocks in his 'catchment area'. T=
his particular story concerned a customer whose TV would periodically not r=
eceive a certain TV channel, even though they were line of site to the tran=
smitter. Said customer was some way up one of the tower blocks, and despite=
 some visits to the abode the problem was not diagnosed. Eventually custome=
r was told to call him immediately the problem recurred and he would come a=
round promptly. In due time said phone call happened, so serviceman goes to=
 the home and sure enough the channel concerned was just visible in the sno=
w that was typ!
 ical of a very weak signal in the days of analogue TV. No matter what he d=
id to the set to attempt to repair the problem produced any improvement, so=
 after some time he ends up standing in customers lounge pondering what the=
 cause of this strange loss of channel was - it was one specific channel, a=
ll the other channels were as strong a signal as they had ever had. His eye=
s are wandering around the apartment as he was thinking, and he realised th=
at son was playing with his train set on the floor - and the loop of track =
was about right size for a dipole at the VHF frequency of the channel conce=
rned. A moments stoppage of the train and breaking a track joint soon resto=
red the picture on the channel of interest.

Another story from the same source concerned a colour TV that would give on=
ly B&W pictures on a certain channel. This was eventually tracked down to t=
he 300 ohm ribbon from the terminals on the back of the cabinet to the tune=
r being secured with a piece of wire looped around a suitable point and the=
n had the ends twisted to secure the ribbon cable conveniently out of the w=
ay. The loop combined with the twisted ends combined to make a tuned circui=
t at the colour burst carrier frequency on this particular channel which ac=
ted as a trap preventing the colour burst from reaching the tuner. A quick =
trim of the amount of twisted portion (which were fairly long) produced col=
our pictures.

--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.