AVR MPX 4CH Dimmer Pack

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Hi I am trying to build a MPX 4CH Dimmer Pack, I chose to use the AT90S4433 in a TQFP package but I am having trouble with it's internal ADC, I have tried the filter suggested in the book and even one someone recomended using a 10uH Inductor and a 100nF capacitor to feed the AVref, and the AVcc, but it is behaving very erratically, ie. I am trying to monitor an analog source wich goes from 0 to 5V and it is only giving me a digital readout for values between 4.62 and 4.88V, if my analog value is below 4.62V it just gives me a readout of 0x00, and the full scale is between 4.62 and 4.88, I really don't know what to do but I am really desperate, you see I am just about to change uC, although I wouldn't like it, I have used many, from Atmel, Intel, Motorola, National and even PIC's, but I had never used the ADC on the Atmel, I have used them on the National's COP they are not as delicate, I need no filters and they work beautifull, but they are not fast enough, that is were Ateml comes in, but I just can't get the ADC to work, please I don't want to change uC, Atmel's is very good... HELP with the ADC

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If you read the appnotes on *any* ADC, you'll find they require clean power supplies. If you're not filtering, you're not doing it right. You may not see the errors if you're discarding the low 4 bits, but they'll be there. You start trying to measure hundredths of a volt, and it will be come extremely obvious.

And it seems to me people *are* helping you, in the main forum area. As Fergus Dixon and Chris Coulson pointed out, the problem is most likely in that bizarre bit shifting and writing to PORTC that you're doing. Which is especially odd since bit 4 is the bit being used as the ADC channel.

--John

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