Friday, 6 July 2012

RFnodes v1.0

RFnode v1.0
Time for a second post. This time with pictures.

These little guys are the Version 1.0 RFnodes I was working on, These were the first version I designed so expected a few issues. It is all part of my self inflicted crash coarse into PCB design and SMD (surface mount). This board is a few weeks old now and I have moved on to better designs since. 

The good
  • They are Arduino based (Atmega328/168) 
  • V-USB bootloader (same as USnooBie)
  • Runs at 12Mhz @ 3.3volts with onboard voltage regulator (AMS1117 3.3)
  • USB or 3 volt coin cell powered (CR2032) 
  • The PCB is designed by me from the ground up (printed in china)
  • Compatible with the USnooBie (as I own a few of them too and over time have found them easier to work with then many Arduinos)
  • Supports V-USB
  • Uses nRF24L01+ 2.4Ghz radio 
  • Mostly SMD parts (and all soldered by hand) 
  • Some parts not SMD so I could change the sides if I wanted
  • 4 digital IOs (2 used for serial)
  • 6 Analog IOs (2 used for I2C)
  • 2 LEDS (Red/Green) 
  • ISP Header (only used for loading bootloader or adding another SPI device)
  • Can consume <0.1mAh in sleepmode and about 0.5mAh idle (read below)
 The Bad
  • The Radio overhang. This was done on purpose for this version of the board so the antenna is free from interference from the main board. After a bit of testing I decided I did not need to position the radio in such a way. 
  • SMD pad sizes. As I am a little new to SMD parts and their required pad sizes on the PCB some of my pads where too small for the part. Well it was only one part, The main power capacitor which I ended up just soldering to the voltage regulator pins.
  • Silk screen. Not all of the silk screen was printed or was too small or mostly off the edge of the board after cutting.   
  • Power consumption. Board was consuming about 17.5mAh so a CR2032 would only last about 6 hours which is less then the maths that said I should be able to get up to about 5 months. Issue turned out to being the AMS1117 power regulator would still consume about 4mAh if power was connected to it's output. I thought it was only meant to consume power if connected to input only. I also found that the radio was consuming about 13.5mAh when idle in RX mode. So after disconnecting the voltage regulator and powering down the radio when not in use I can the power consumption to less then 0.3mAh and less then 0.1mAh when in sleep mode.     
My finger compared to it's size, all soldered by hand (mostly my off hand)

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