Post by thread:Log A to D Convertors

Hi all, I'm pretty sure the answer to this one is no, but do any of the PICs have internal Logarythmic ADCs? If not, can anyone recommend to me a Log ADC which can, say, compress 4 decades into 8 bits, preferably serial and in an 8 pin package? If not, I would settle for any Log convertor recomendations. I'm trying to use photodiodes to measure light levels which vary a great deal and I need good resolution, even at low levels. Thanks very much, Sean +--------------------------------+ | Sean Breheny | | Amateur Radio Callsign: KA3YXM | | Electrical Engineering Student | +--------------------------------+ Save lives, please look at http://www.all.org Personal page: http://www.people.cornell.edu/pages/shb7 spam_OUTshb7TakeThisOuTcornell.edu Phone(USA): (607) 253-0315 ICQ #: 3329174

Sean asked: > >I'm pretty sure the answer to this one is no, but do any of the PICs have >internal Logarythmic ADCs? If not, can anyone recommend to me a Log ADC >which can, say, compress 4 decades into 8 bits, preferably serial and in an >8 pin package? If not, I would settle for any Log convertor recomendations. > > >I'm trying to use photodiodes to measure light levels which vary a great >deal and I need good resolution, even at low levels. > One possibility would be to use a log op-amp ahead of the A/D. There are lots of examples of suitable circuits in the literature. Also, the TI TSL230 series detectors have programmable sensitivity and direct digital output. It should be possible to cycle through several levels of sensistivity and select the one that is mid-scale for current conditions. Reg Neale