I have a atmega8535 in DIP format.
Now the spec sheet says there are more ADC channels on the square TQFP format of this chip and that (exclusively on that format) can be differential inputs, two with programmable gain.
This may be an important factor in what I aim to do.
I see similar additional channels in the higher spec chips but don't find any mention of differential inputs.
Am I not digging deep enough into the doc , or has the nice feature been dropped on the more recent chips?
Thanks to anyone who can point me at the answer.
– Four PWM Channels
– 8-channel, 10-bit ADC
8 Single-ended Channels
7 Differential Channels for TQFP Package Only
2 Differential Channels with Programmable Gain at 1x, 10x, or 200x for TQFP
Package Only
Datasheet for 8535 and 8535L: http://www.atmel.com/Images/doc2502.pdf
The analog inputs are described on pages 206 through 223.
The differential feature MIGHT work on the PDIP package:
Page 206 Note: 1. "The differential input channel are not tested for devices in PDIP and PLCC Package. This feature is only guaranteed to work for devices in TQFP and QFN/MLF Packages."
Am I not digging deep enough into the doc , or has the nice feature been dropped on the more recent chips?
Some of the ATtiny processors have differential inputs.
thanks, that's what I was looking for.
the doc I had was just the summary and it was a bit sparse on detail.
Mind you, my thinking was that I would have better accuracy
The device also supports 16 differential voltage input combinations. Two of the differen-
tial inputs (ADC1, ADC0 and ADC3, ADC2) are equipped with a programmable gain
stage, providing amplification steps of 0 dB (1x), 20 dB (10x), or 46 dB (200x) on the dif-
ferential input voltage before the A/D conversion. Seven differential analog input
channels share a common negative terminal (ADC1), while any other ADC input can be
selected as the positive input terminal. If 1x or 10x gain is used, 8-bit resolution can be
expected. If 200x gain is used, 7-bit resolution can be expected.
Not sure what " 8-bit resolution can be expected." is supposed to mean. They're 10 bit adc's so it must still be 10bit resolution. If they mean accuracy, is that the same as the absolute accuracy of each single ended channel given as 8bit accurate?
That will give me about +/- 0.5% on the product of two inputs which is just about good enough for what I need.
However, upto 250us for each conversion .... ouch.
I may need to use and external ADC. 