Converting Arduino PWM to Xbee Analog Input

Other Hardware General Electronics
1

Hey everyone,
I would like to send analog signal through Xbee.
As I researched on internet,(pls let me know if i'm wrong) I need to do RC filtering between Arduino's PWM pins and Xbee Analog input pins, otherwise the Xbee pins will be burned due to voltage mismatch.

So here is my question, how many ohm of resistor and uf of capacitor I need in order to synchronize the voltage/frequency between arduino and xbee.

Reference: http://www.makingthings.com/wiki/analog-output

2

The "Time Constant" (for the voltage to reach 63% of final value) is R * C so .0047 seconds (4.7mS) in this case.

In 10 T (time constants) the value will have reached 99% of it's final value. Thats .047 S in this case.

Since the Xbee isn't going to try to follow changes, maybe use 10 uF for .47S to "well-settled"..

But you have to decide how fast the analog value must be "Followed"....

3

A discussion of PWM filtering is to be found here:-
http://www.thebox.myzen.co.uk/Tutorial/PWM.html

4

I need to do RC filtering between Arduino's PWM pins and Xbee Analog input pins, otherwise the Xbee pins will be burned due to voltage mismatch.

A low pass filter will convert an arduino pwm signal to a constant analog voltage in the range of 0-5vdc depending on the duty cycle value of the pwm signal. This would not prevent 'burned due to voltage mismatch' if the Xbee cannot handle a max of 5vdc input voltage. So you may be mixing up two different requirements. Do you require a constant analog dc voltage or are you concerned about what max voltage a Xbee can safely handle? A low pass filter won't solve that latter concern by itself.

Lefty

5

could you explain what exactly you want to do? Why wouldn't it be sufficient just to send values through the xbee?

markbee

6

markbee:
could you explain what exactly you want to do? Why wouldn't it be sufficient just to send values through the xbee?

markbee

It may be that the Xbee is a 3.3vdc device and not able to handle 5vdc signals?

Lefty

7

I have been working on the same application. I have added the simple filter with low ripple. But as soon as I add the output of the filter to Xbee, somehow it will change back to pulse again. It seems that the Xbee takes samples from the ripple and adds it to the original value. To be honest I couldn't find a 100% logical reason for this. The values keeps changing. Any idea why this happens? Would appreciate any help. Thanks