Electronics FAQ

This is the final post in a series of post that explains how I installed an electrical energy meter in my house and connected  it to the internet. Here are the steps involved: Installing a 3 phase energy meter in your home [ Blog post here ] (I used Selec MFM383C Modbus capable energy meter, connected it to my router using USB<>RS485 interface based on FT232RL and MAX485) Modbus capable energy meter Installing OpenWrt 15.05 Chaos Calmer on TP-LINK TL-MR3020 [ Blog post here ] (required adding a USB hub to it, a USB flash drive to hold the rootfs, an FT232RL widget  for getting console access to the router over serial and another FT232RL based USB<>RS485 UART for interfacing to the energy meter using modbus. Instead of TL-MR3020, you can use TL-MR3040 as well which has its own battery pack in it.) TL-MR3040 (White color) with a USB hub sporting an 8GB Flash drive and USB<>RS485 convertor. A TL-MR3020 with a USB hub (Flash drive in one of the...

The Bulbs So I took 3 bulbs of 40 Watts, 60 Watts and 100 Watts respectively and measured the hot and cold resistances I used the Philips softtone frosted lamp series. Price: 40 Watts : Rs 20 60 Watts : Rs 20 100 Watts  : Rs 21 Blub packs - Front Blub packs - Back Cold Resistances The cold resistance readings were as follows: 40 Watts : around 97.6 Ohms 60 Watts : around 71.4 Ohms 100 Watts : around 39.5 Ohms Measuring Cold resistance of 40W Bulb Measuring Cold resistance of 60W Bulb Measuring Cold resistance of 100W Bulb Hot Resistances (Calculated) Calculated values of hot resistance can be obtained using the formula: Resistance = (Voltage^2) / Power In India the AC voltage RMS value is 230 Volts. So we get the hot resistances as: 40W Bulb : (230*230) / 40 = 1322.5 Ohms 60W Bulb : (230*230) / 60 = 881.67 Ohms 100W Bulb : (230*230) / 100 = 529 Ohms Hot Resistances (Measured) To get the actual values of the hot resistanc...

In my efforts to smartify my house, one of the first things I did was to install an energy meter and connect it to the internet. I connected a TP-link TL-MR3020 to a Modbus capable energy meter to do this. Here are my efforts this far: Installing a 3 phase energy meter in your home Installing OpenWrt 15.05 Chaos Calmer on TL-MR3020 The next involved writing and compiling some native code to interface with the energy meter using Modbus. The Selec MFM383C energy is connected to TL-MR3020 over UART. My TL-MR3020 has a USB hub connected to it. One of the slots has a 8GB USB Flash drive in it with the rootfs on it. Another slot has FT232 and MAX485 based USB-UART bridge. I use this USB-UART communicate with my mfm383c using Modbus. ------------ Problem statement: Cross compile C code into an OpenWrt ipkg in case which requires fetching and compilation of dependent libraries as well. Detailed problem statement: Cross compile a piece of software (native, C program) ...

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...