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31  Products / Arduino Yún / Re: view all pin states from webpage on: July 27, 2014, 09:19:55 pm
Replace ‘, ’ with  '.
 and Replace “, ”  with ".
32  Using Arduino / Networking, Protocols, and Devices / Re: I2C Communication between Arduino Uno and Cypress CY8C20160 Capacitive Sensor on: July 25, 2014, 03:02:50 pm
http://www.picaxeforum.co.uk/showthread.php?25752-Touch-sensing-i2c-chip

https://github.com/akafugu/TouchCY8C201A0
33  Products / Arduino Yún / Re: Python script to monitor Yun wifi connection on: July 25, 2014, 10:35:30 am
The reason external antenna is needed is:

  • On board chip antenna has average Gain  -0.5 dBi  
  • Yun's  transmit power is only 17 dBm.
  • Yun is siting at metal case.
  • The distance between Yun and WIFI router is far

Friis Transmission Formula with Propagation Law



  • R = Maximum range for communication link
  • N = Propagation Law (N=2 for line-of-sight, N=4 for urban environments)
  • PT= Transmit power
  • GT= Total antenna gain
  • λ = Wavelength
  • PR= Receiver sensitivity
  • FM= Fading margin

if in urban environments;-

  • Every 12 dBm receiver sensitivity gain will be double the distance.
  • Every 12 dBi antenna gain will be double the distance.
  • Every 12 dBm Transmitter power gain will be double the distance.


in line of sight environments;-

  • Every 6 dBm receiver sensitivity gain will be double the distance.
  • Every 6 dBi antenna gain will be double the distance
  • Every 6 dBm Transmitter power gain will be double the distance.

http://forum.arduino.cc/index.php?topic=175577.msg1304059#msg1304059

PC or  tablet has higher  gain antenna and transmit power could be much higher than Yun.

P.S. since use different  RF chip set, The  Receiver sensitivity could be higher than  Yun as well.
34  Products / Arduino Yún / Re: Wifi connection lost, do I have some logs? on: July 25, 2014, 10:00:39 am
...
Signal           Noise   RX Rate                                           TX Rate
-88 dBm   0 dBm   28.9 Mbit/s, MCS 3, 20MHz   21.7 Mbit/s, MCS 2, 20MHz

if I go in the yun luci (advanced panel) I can see the ip of the router with those values:
-71 dBm   -88 dBm   13.0 Mbit/s, MCS 1, 20MHz   28.9 Mbit/s, MCS 3, 20MHz
...

-88 dBm  as Noise  is too high, your s/n (Signal-to-noise ratio) is too low ( only 17 dBm) .  check your wifi channel spectrum,  select less crowded channel.
35  Products / Arduino Yún / Re: Python script to monitor Yun wifi connection on: July 25, 2014, 09:48:28 am
Understanding Wifi Signal Strength:
Wireless signal strength is traditionally measured in either percentile or dBm (the power ratio in decibels of the measured power referenced to one milliwatt.)  The level of 100% is equivalent to the signal level of -35 dBm and higher, e.g. both -25 dBm and -15 dBm will be shown as 100%, because this level of signal is very high. The level of 1% is equivalent to the signal level of -95 dBm. Between -95 dBm and -35 dBm, the percentage scale is linear, i.e. 50% is equivalent to -65 dBm.

Get Wireless signal strength in dBm at Yun:

Code:
iwconfig 2>&1 | grep 'Signal level'
Link Quality=70/70  Signal level=-37 dBm

My reading now:

Code:
root@Arduino:~# iwconfig 2>&1 | grep 'Signal level'
          Link Quality=70/70  Signal level=-21 dBm

Adjust router antenna and make router and Yun closed together as well as  add  high gain antenna into Yun will bring Signal level up.

Should not bring 'Signal level' too high,  It could be saturation  the RF circuit.
36  Products / Arduino Yún / Re: Yun i cannot install PHP on: July 25, 2014, 09:31:35 am
Can you

Code:
ping google.com
37  Products / Arduino Yún / Re: How to invoke cd command from Process.runShellCommand() : Please advise - Thanks on: July 25, 2014, 09:30:28 am
Normally use absolute path instead of cd to parent directory.
38  Products / Arduino Yún / Re: How to expand the storage memory on the Yún on: July 25, 2014, 09:28:12 am
hi ,
          when the running the script , i got the following error.
"err formatting fat32"
Please  help me to resolve this issue.Size of the micro sd card is 8GB

take out SD card, put it into Windows machine to test format.

or

at Yun

Code:
fdisk /dev/sda
mkdosfs -F 32 /dev/sda1


partition and format SD card.
39  Products / Arduino Yún / Re: How to expand the storage memory on the Yún on: July 25, 2014, 09:24:24 am
...
is there a way to access the filesystem that is still on the flash, without removal of the SD card?
E.g. how can I access the /etc/config/fstab file on the Yun flash?

Power off Yun , take out SD card. power on Yun again to access flash.
40  Products / Arduino Yún / Re: [Please help] [Not working]Connecting the Arduino Yun to WIFI on: July 24, 2014, 07:07:39 am
1. Connect ethernet cable to Yun

2. Uploaded the YunSerialTerminal sketch

http://arduino.cc/en/Tutorial/YunSerialTerminal

output of:

Code:
ifconfig
41  Products / Arduino Yún / Re: zero conf protocol and node modules compiling on: July 24, 2014, 07:00:54 am
Steps for npm module (node_mdns) compilation:

https://github.com/arduino/openwrt-packages-yun/issues/8
42  Products / Arduino Yún / Re: Problem with microSD on: July 24, 2014, 06:53:09 am
output of

Code:
fdisk -l
43  Products / Arduino Yún / Re: How to Arduino Yun support Creative Live! VISTA VF0470 webcam? on: July 24, 2014, 06:50:11 am
...
recompile libgd with freetype support.

nano ~/OpenWrt-yun/package/feeds/packages/gd/Makefile

Code:
CONFIGURE_ARGS += \
        --enable-shared \
        --enable-static \
        --disable-rpath \
        --without-x \
        --without-fontconfig \
        --without-freetype \
        --with-jpeg=$(STAGING_DIR)/usr \
        --with-png=$(STAGING_DIR)/usr \
        --without-xpm \
        --without-iconv

remove " --without-freetype \" then recompile libgd. then remove installed libgd force install new revision one.  I have not chance to test it but you should go ahead try it yourself.

44  Products / Arduino Yún / Re: How to Arduino Yun support Creative Live! VISTA VF0470 webcam? on: July 24, 2014, 06:48:29 am
Work around:
...
Code:
fswebcam  -i 0 -d v4l2:/dev/video0  --no-banner  --jpeg 95  --save test.jpg
--jpeg 95 will increase quality to 95%.
...

--no-banner

45  Products / Arduino Yún / Re: Communication between 2 Arduino Yunv over WiFi on: July 23, 2014, 04:03:31 pm
Plan C:

Use mesh network:

http://forum.arduino.cc/index.php?topic=217078.msg1815907#msg1815907


Plan A: 1:N
Plan B: 1:1
Plan C: N:N
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