Thursday, January 23, 2014

Using TL-MR3020 as an IoT Node instead of Arduino Yún

After putting up my home weather station (blog post here) using TL-MR3020, I spend some time thinking if I could continue using this pocket router for future projects, here are my thoughts:

In India an Arduino Yún (INR 5903 from rhydoLABZ). But if instead of that if you go for the combination:
TL-MR3020 Pocket Router (INR 1395 from flipkart)
+ Portronics Combo USB and Card Reader (INR 299 from Portronics)
+ SanDisk Cruzer Blade 8 GB Pen Drive (INR 304 from flipkart)
+ Arduino Micro (INR 1820 from rhydoLABZ)
Total come would come to INR 3818 which is 35% cheaper than the Yún.
The combination can do everything the Yún can do and much more:

  • Linux Processor: TL-MR3020 has the same CPU (Atheros AR9331) as Yún and runs the same OS OpenWRT
  • Microcontroller: Arduino Yún has ATmega32u4 on it, same as the one on Arduino Micro
  • SD Card Reader: TL-MR3020 can use the one on the Portronics hub
  • WiFi & Ethernet: Both have that
  • Power Supply: TL-MR3020 comes with a travel charger, Arduino Yún doesn't come with a power supply.
  • USB Host Port: Since the combination has a USB hub, you get two more ports as compared to just the Yún.
  • Flash memory available to OpenWRT: Even though Yún has 16MB of flash whereas MR3020 has only 4MB, but if you mount the rootfs on the USB flash drive, you get to access whooping 8GB worth of memory
  • RAM available to OpenWRT: Yún has 64MB, MR3020 has only 32MB - not a biggie when it comes to running lightweight applications.
Another idea: use FT230X to bit bang.
Use a TL-MR3020 router (INR 1395) with FT230X to interface directly to DHT11 using bitbanging mode.

  1. DHT11 (INR 300) is a cheaper athough less accurate alternative to using SHT11.
  2. FT230X is a newer more inexpensive (more than 1 USD cheaper) variant for FT232RL with a few less RS232 handshake pins, which should be okay for our purposes - we only need a single big banged pin to interface to DHT11.
  3. If we write the code in C and use libFTDI (which is also available for OpenWRT/MIPS), then we will definitely be able to fit the application executable in the 820KB of flash which is available on TL-MR3020 after freshly installing OpenWRT on it - we won't need a USB hub and USB flash drive for expanding the storage space.

I think this can result in a temperature+humidity station for about INR2000


Post a Comment