XBee ADC value has a 10mV difference

XBee & XBee Gateway XBee - 802.15.4
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1

Hello,

I have a XBee S2B router which send its ADC values to the coordinator (once every minute)

When there is a low Voltage value on the pin, below 10mV it is seen always as 0. (did this test with a few different Xbee’s).
When the input on the ADC is above 10mV the ADC gives numbers above 0.

A few examples of ADC measurements:
used (ADC/1023)*1.2 to calculate the voltage from the ADC.

68.4mV Multi meter; ADC 49 => 57.5 mV
300.7mV Multi meter; ADC 248 => 290.9 mV
928.0mV Multi meter; ADC 783 => 917 mV

Firmware version Router: 22A7

Using the https://pypi.python.org/pypi/XBee XBee-2.1.0 library to readout the frames/values.

My question is why does the ADC does not detect values below 10mV and why are the ADC readings 10mV lower?

Thanks!
Jasper

2

Jasper, what is the actual API frame provided from the radio?

3

Hi mvut, thanks for your question.

7E 00 14 92 00 13 A2 00 40 B4 E3 54 55 FB 01 01 00 00 81 03 0F 0A CC D2

- Start delimiter: 7E
- Length: 00 14 (20)
- Frame type: 92 (Zigbee IO Data Sample RX Indicator)
- 64-bit source address: 00 13 A2 00 40 B4 E3 54
- 16-bit source address: 55 FB
- Receive options: 01
- Number of samples: 01
- Digital channel mask: 00 00
- Analog channel mask: 81
- Analog sample: 03 0F 0A CC

So two samples first one ADC-0 (030F) second one ADC-7 (power level, 0ACC).
030F = 783

783/1023*1.2= 918.4 mV
multiemeter gives 927mV

Still around 10mV difference.

Thanks,
Jasper

4

and an other sample with low Voltage, below 10mV:

Zigbee IO Data Sample RX Indicator

7E 00 14 92 00 13 A2 00 40 B4 E3 54 55 FB 01 01 00 00 81 00 00 0A CC E4

- Start delimiter: 7E
- Length: 00 14 (20)
- Frame type: 92 (Zigbee IO Data Sample RX Indicator)
- 64-bit source address: 00 13 A2 00 40 B4 E3 54
- 16-bit source address: 55 FB
- Receive options: 01
- Number of samples: 01
- Digital channel mask: 00 00
- Analog channel mask: 81
- Analog sample: 00 00 0A CC
- Checksum: E4

So this gives 00 00.

The multimeter give: 5.4mV

Thanks,
Jasper

5

Jasper, you can see with the actual API frame that you are not getting a 0 value. If you calculating a 0 value from the 00 0A CC value, then there is an issue with your Code and not the radio.

6

mvut thanks for the quick reply.

This frame has two ADC value, I believe it should be read like this:

  • Analog channel mask: 81
  • Analog sample: 00 00 0A CC

00 00 = ADC-0 (should be 5.4mV)
0A CC = ADC-7 (Supply voltage High Threshold V+)

Below I took a new sample frame without ADC-7 (Supply voltage High Threshold V+):
Zigbee IO Data Sample RX Indicator

7E 00 12 92 00 13 A2 00 40 B4 E3 54 55 FB 01 01 00 00 01 00 00 3A

- Start delimiter: 7E
- Length: 00 12 (18)
- Frame type: 92 (Zigbee IO Data Sample RX Indicator)
- 64-bit source address: 00 13 A2 00 40 B4 E3 54
- 16-bit source address: 55 FB
- Receive options: 01
- Number of samples: 01
- Digital channel mask: 00 00
- Analog channel mask: 01
- Analog sample: 00 00
- Checksum: 3A

So this give ADC-0=00 00
and my multi meter gives 9.3mV

Thanks,
Jasper

7

Jasper,. the only thing I can think of that would cause this is if you had the lines switched and are actually providing a negative voltage. In that situation, the value would be 0.