Pages: [1]   Go Down
Author Topic: adxl3xx example in IDE  (Read 716 times)
0 Members and 1 Guest are viewing this topic.
0
Offline Offline
Jr. Member
**
Karma: 0
Posts: 55
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I've got  a question about one of the examples in the IDE.

For the adxl3xx it has supply maximum voltage of 3.6V. However, in the IDE it says this

Quote
  // Provide ground and power by using the analog inputs as normal
  // digital pins.  This makes it possible to directly connect the
  // breakout board to the Arduino.  If you use the normal 5V and
  // GND pins on the Arduino, you can remove these lines.

Is this example safe? It works but right now I refrain from using it for long periods.
« Last Edit: February 13, 2010, 07:08:08 pm by regomodo » Logged

Seattle, WA USA
Online Online
Brattain Member
*****
Karma: 548
Posts: 46003
Seattle, WA USA
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Which ADXL3xx accelerometer do you have? The one that Sparkfun sells (http://www.sparkfun.com/commerce/product_info.php?products_id=849) has this on the data sheet:

Quote
Wide supply voltage range: 2.4 V to 5.25 V
Logged

0
Offline Offline
Jr. Member
**
Karma: 0
Posts: 55
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I have the adxl335 at the sparkfun page it says

Quote
There is no on-board regulation, provided power should be between 1.8 and 3.6VDC.

It's likely i've damaged mine right?
« Last Edit: February 14, 2010, 11:13:20 am by regomodo » Logged

Seattle, WA USA
Online Online
Brattain Member
*****
Karma: 548
Posts: 46003
Seattle, WA USA
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
It's likely i've damaged mine right?

You haven't done it any favors. It's not difficult to create a voltage divider, using 2 resistors so that the device can be powered by a digital pin.

pin (5V) --> R1 -+-> R2 --> gnd
                          |
                       adxl3xx

If R1 is ~3K and R2 is ~6K, the voltage to the adxl3xx will be ~3.67V. Make R1 a little larger or R2 a little smaller to drop the voltage going to the accelerometer. Measure with a voltmeter to be certain. Compute the current flow for you resistors to be sure that you don't exceed the current capabilities of the digital pin (40mA max; 20mA recommended). Make sure the resistors can handle the current flow, too.
Logged

0
Offline Offline
Jr. Member
**
Karma: 0
Posts: 55
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

When I first used the accelerometer I used the 3.3v output and tied Aref to 3.3v as well and that worked fine.

I then noticed the adxl3xx example in the ide and saw that you could slot the board into the 6 analog pins directly and naively thought the example was safe. "adxl3xx" is misleading.
Logged

Pages: [1]   Go Up
Jump to: