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Showing posts from December, 2015

Installing a 3 phase energy meter in your home

About 2 years ago, I decided that it would be a good idea to log how much electricity I was using. If the endeavor resulted into an internet connected device, that would be even better.

So I set out looking for an energy meter. I was looking for one which had an interface which would all me to connect it to the computer (or Raspberry Pi or an OpenWrt device).

Since I have 3 phase supply coming into my house. There are 5 wires coming into my main electrical distribution panel: Red, Yellow, Blue, Neutral and Earth. The RMS voltage between any one of the 3 live wires and neutral is 230 volts.

I selected the Selec MFM383C which is a 3 phase meter with Modbus interface. I also used 3 nos. current transformers: Selec SPCT-62/40-100/5-1.5(1T)-0.5 one each for each phase line (Red, Yellow and Blue). These transformers are of the ratio 100:5.

The connection scheme is as shown below. One has to take care to make sure the direction of wire passing through the current transformer and the order o…

OpenWrt 15.05 Chaos Calmer on TL MR3020 with rootfs on external usb drive

The latest version of OpenWrt is quite bulky. Although it feats neatly within TL-MR3020's 4MB flash, doesn't leave enough space to install the modules required to shift the root file system to an external drive.


In previous versions of OpenWRT, you had 840KB of space left on internal 4MB flash to install the essential kernel modules for usb, usb mass storage and ext4 which are all essential for mounting USB flash drive. My Weather Station used TL-MR3020 flashed with OpenWrt 12.09 and used this methods.
In the latest version just about a few hundred kilobytes are left after flashing the image which aren't enough to install the modules required for mounting USB flash drives. So we have to resort to the following steps:


Open up your TL-MR3020 and solder in a USB-UART (FT232RL) board to gain access to its serial port.Install the toolchain for compiling OpenWRT on your 64-bit Ubuntu LaptopCompile OpenWrt for TL-MR3020 on your ubuntu laptop. While doing so, we will include the mo…