Build Instructions

Collapse

• 1

  How it Works

  Background On Current and voltage measurement

  Measuring Voltage is quite easy where all you have to do is connect the voltage you want to measure to an ADC (analog to digital converter) for a microcontroller to then read, and display the values for you. An ADC pretty much samples the analog voltage at certain points in time, and stores those values as bits. The higher the bit resolution, which is the amount of samples the ADC takes of the analog voltage, the better the accuracy. Measuring current can be done in many different ways, but I'll only focus on the one this project uses which is using a current shunt. A current shunt is just a resistor connected in series with the load you are measuring, and according to Ohms Law, the current running through this resistor will create a voltage drop across the resistor equal to I times R. The current through the shunt will be the same as the the current running through the load as it is connected in series with the load. If the value of the shunt is known then the current through the load will be equal to voltage drop across the shunt/resistance of shunt. Shunts can be connected in the high or low side where high side is when the current shunt is connected to the positive side of the load, while low side is connected to the ground side of the load. I chose high side sensing for this project.

  About The Components

  This project uses the INA226 power monitoring IC to measure the voltage, and current. It achieves this by measuring the voltage across the shunt resistor, and calculates the current running through the load as the voltage is simply measured by the ADC of the INA226. The heart of this project is the ATMEGA328p, since it reads the values from the INA226 through I2C, and displays these values to the OLED display through again, I2C. The current shunt is a 5mΩ resistor with 1% tolerance rated to be 2W which creates a voltage drop that the INA226 measures. The SSD1306 is a typical display that is available everywhere that is commonly used in arduino project where you simply power it up, and feed it information through the I2C line.

• 2

  Schematic

  The ATMEGA328p is pretty much the same as an Arduino mini, and to program an Arduino mini you would need a FTDI programmer in order to convert the USB to serial communication. In order to program the ATMEGA328p, the FTDI programmer needs to connect to the ATMEGA by using pins DTR, RX, TX, CTS, POWER, and GROUND. Not only do you have to program the ATMEGA, but since the chip is blank it needs to be bootloaded, and to bootload the chip you need to connect an Arduino uno to the chip with pins 15, 16, 17, and 29. Programming, and bootloading the chip will be explained in the steps below. The two 10k resistors are on pins 28, and 27 of the ATMEGA as those are the I2C pins (SDA and SCL). These two pins need a pull-up resistor to function correctly where the display, and INA226 use I2C communication which is why they have pins labelled SDA, and SCL (serial data and serial clock). VBUS of the INA226 is the point (with respect to ground) that you measure the voltage with, IN+ goes to the positive side of the shunt, and IN- goes to the load side of the shunt, the alert pin is used to alert the user of fault conditions.

• 3

  The PCB

  This board measures 27mm x 28mm, and it takes a 5v-40v input which passes through the LM317 regulator which powers the entire board with 3.3v. The shunt resistor is on the bottom of the board, and can be connected to the load through the exposed contacts on the board. The board contains no holes as I wanted to save space, and reduce contact resistance, which was done to make sure the INA226 was giving accurate readings. To program the board, there is a female header for the FTDI programmer, and to bootload the board there are exposed contacts on the back of the board. The OLED display goes on the back of the board where the board must be bootloaded first before placing the display on it, since they are both located on the back.

View all 6 instructions