Go Down

Topic: Xbee woes (Read 1 time) previous topic - next topic

imagiro1

What is the max input voltage for the ADC pins? I thought it was 3.2V and not 1.2V like I've been reading.

Second, I am trying to setup ADC 0 and 1 to transmit to PWM 0 and 1. Here are my settings:

Transmitter:
DL 1234
MY 5678
D0 2
D1 2
IR 14
IT 5

Receiver:
DL 5678
MY 1234
PO 2
P1 2
IU 1
IA FFFF

Using the terminal I am able to see the data stream coming into the receiver. However, the voltage changes from 0V to 3.2V (no in between values) when I moved the joystick from 0-1.2V. I do not need the data stream, I need the voltage at pin 6 and 7 to reflect the movement of the joystick. Any ideas ? Thanks.

PaulS

Quote
What is the max input voltage for the ADC pins?

On the XBee? 3.3V.

Quote
I thought it was 3.2V and not 1.2V like I've been reading.

Reading where?

markbee

#2
Jul 24, 2011, 06:56 am Last Edit: Jul 24, 2011, 06:58 am by markbee Reason: 1
According to the datasheet (page 17 - "DC Characteristics of the XBee/XBee?PRO") the ADC input voltage range on a XBee series 2 is typical 1.2V and max. VREFI (internal reference voltage).

There is a note on the "DC Characteristics of the XBee/XBee?PRO" table referring to the ADC input also:

"Note - The signal-ended ADC measurements are limited in their range and only guaranteed for accuracy in
the range 0 to VREFI. The nature of the ADC's internal design allows for measurements outside of this range
(+/- 200mV), but the accuracy of such measurements are not guaranteed."

I can't find any maximum numbers for the ADC inputs in the datasheet though.

A simple way to step down the original voltage (in this case 3.2V) might be a simple voltage divider consisting of two resistors. If you look for very fast signals you might consider specialized level shifter ICs.

markbee

XBee blog: http://lookmanowire.blogspot.com/

imagiro1

I should of added it's a Series 1. I looked at the datasheet again. It says from ADC Vref is from 2.08V to V_DDAD which is connected to VCC. VCC is 3.4V. So it looks like PaulS was right. Again  :) I'm pretty sure you've answer more of my questions.

But it still doesn't explain why I don't see the pin 6 or 7 change when I move the joystick. Ugh.

imagiro1

Vref according to the Xbee pdf says max is V_DDAD which is connected to Vcc. It's not. Connect Vref to Vcc. Problem solved.

Go Up