Oznog
Active Member
dknguyen said:I2C? pshh! Who needs I2C when you got CAN! But yeah, by far the worst thing I find with the 33F is that I need to level convert everything to communicate with 5V. Even worse is reducing 5V analog signals to be accepted by the 33F's 3.3V ADC, particularily when you need very very precise measurements like integrating gyroscope or accelerometers readings. It kind of really blows when you consider the changing offsets for the op-amp buffers and varying resistance of the resistive dividers, it's enough to add tens of mV of error which is ginormous when you are integrating the thing.
Why no 5V 33F?! Why? Why?! WHY?! Either that or 3V everything else which is a bit of a problem for ring gyros right now
CAN is sucking for me due to the need for an external transceiver- and I'm kinda bummed by the idle current of some of the more "affordable" transceivers. Also the wiring limitations with the terminating resistors is inconvenient.
I believe you are mistaken on this 3.3v vs 5v problem's existance.
The dsPIC33F migration document says that ALL inputs are "+5v tolerant". So you're supposed to be able to put +5v straight into any pin other than Vdd. The +3.3v output voltage should be interpreted as a logical high level by most devices. My understanding of this device is of course in its "early stages" so I hope I didn't jump to any conclusions in this area.
I don't think an analog voltage above Vdd can be read by the ADC though. AFAIK Vref cannot be taken above Vdd but I'll need to read up on it. However, it's unnecessary for most of these devices. For example, the Whetstone Bridge used in most accelerometers and pressure sensors works just dandy on any reduced voltage. You just can't exceed the Vdd-Max in the device spec sheet. Now those devices with a built-in output amp may not work on Vdd<5v but those are in somewhat of a minority.
In fact I've been noticing many of the newer accelerometers are rated for a MAX of 3.3v and can't even be run off a 5v system without reducing the Vdd.
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