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[DPRG] Sanity Check: Connecting 3.3V Accelerometer to 5V AVR
Subject: [DPRG] Sanity Check: Connecting 3.3V Accelerometer to 5V AVR
From: Dean Hall
dwhall256 at gmail.com
Date: Mon Dec 10 16:35:32 CST 2007
James,
Based on your description, I think you have it right. No, you don't
need level converters. Be sure the AVR's AVCC has the +5V, too.
Then, you can optionally apply +3.3V to the AVR's AREF pin to give
the ADC readings more resolution. In this configuration, an 8-bit
reading will give 255 when reading 3.3V. If you apply +5V to the
AREF pin, then the maximum 8-bit value you can get is 255 * 3.3 / 5 =
168 (approx).
Restated: Apply +3.3V to AREF and your readings will swing from 0..255.
Apply +5V to AREF and your readings will only vary from 0..168.
!!Dean
On Dec 10, 2007, at 22:14 , jl_harris at juno.com wrote:
> DPRG,
>
> I'm connecting a (+3.3V) 3-axis accelerometer (Freescale MMA7260Q)
> to my (+5V) AVR ATmega168. Both the devices will share a common
> ground and all the accelerometer's select/mode lines are connected
> to pullup resistors to +3.3V or directly to ground.
>
> My mind tells me I can connect the accelerometer's 3 analog outputs
> (X,Y,Y axes range: 0V to 3.3V) directly to the analog inputs (ADC0
> thru ADC2) of my (5V powered) AVR.
>
> However, my mind has misled me before so I wanted a "Sanity Check"
> before I power up and let all the wonderful magic smoke out of my
> cool MEMS Accelerometer.
>
> So what do you all think?? Can I do this without level converters
> on the accelerometer analog outputs?
>
>
> Thanks,
> James
>
>
>
>
> .
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