ATMega vs. PICAXE and AGND/VREF- for low range of ADC conversion

[peekay]

Hi all, just simple question: I'am using PICAXE 18M2 controller which allows me to do ADC conversion of voltages which has low ADC range above the GND. This is achieved by using VREF- pin. ADC is then doing conversion in range between VREF- and VREF+.
Is it possible to do this also with ATMega AVR ?
My source voltage signal from sensor is offset to approx. +1.6V above GND. Is ATMega suitable for such operation or should I stick with PICAXE ? From ATmega DS I can see there is no such pin VREF- or AGND. In future I would like to migrate from Picaxe to ATmega and I am just checking how feasible migration is.
Thanks a lot.
Peter

 

[msharmavikram]

why dont you try msp430 series... ? atmega basic ones doesnt have the feature. you will hav to select the IC among many. however in msp430 which is basically for small signals can do you job brilliantly. (it can convert of the order mV or less)

 

[peekay]

why dont you try msp430 series... ? atmega basic ones doesnt have the feature. you will hav to select the IC among many. however in msp430 which is basically for small signals can do you job brilliantly. (it can convert of the order mV or less)

Well, yeah I am curious about MSP430 and I can afford now to choose the controller since I am at the beginning of learning C libs for MCU. Thank you for opinion.

 

[msharmavikram]

U can purchase one evm board for $5!! TI provides it.. its called launchpad and u can program it. have a try.

 

[milind.a.kulkarni]

Hi,
I have a different thought on this ...What I will suggest you ... First note down the sampling period and resolution of ADC that you are intended to get.... Any inbuilt ADC in the Micro-controller comes with the requirement of additional Logic and averaging methods for recorded values to be part of logic to get better measured signal value ( In a ways to say that one need to have better SNR ( Signal to Noise ratio ) )....So in such situations it is always better to have external ADC modules as a part of your hardware ....As doing this you will isolate the analog and digital sections independent of each other .... However it generally put additional component on the board ....But as you mentioned you are having negative reference voltage concept .... I feel that you have it is requirement in your design....If 8 bit resolution is enough you can even explore ADC0809 as an option too...

Good Luck

 

[peekay]

Yeah, you are right. Actually that was my original intention, however I was trying to source external ADC with I2C interface which is fairly easy to use but unable to source it for reasonable price here in Czech Republic. Now I am rethinking external ADC again however had to settle down with SPI interface. I can source cheaply MCP3202 which is 12bit differential ADC.