Profile：Simple USB Power Tester with OLED Display
Open source license: CC-BY-SA 3.0
Simple USB Power Tester based on ATtiny25/45/85 and INA219. The device measures voltage, current, power, energy, capacity and displays the values on an OLED screen. You can switch between different screens by pressing the SET button.
The device is equipped with a USB-A plug for the input and a USB-A socket for the output, so that it can be plugged between the power supply and the consumer. D+ and D- are passed through so that the consumer can negotiate the charging protocol.
An INA219 is used to measure voltage and current. The INA219 is a current shunt and power monitor with an I²C-compatible interface. The device monitors both shunt voltage drop and bus supply voltage, with programmable conversion times and filtering. A programmable calibration value, combined with an internal multiplier, enables direct readouts of current in amperes. The selected shunt resistance of 8mΩ enables both a very small influence on the circuit and a measurement with a resolution of 1mA. For an accurate measurement, a shunt resistor with a low tolerance (1% or better) should be selected.
The INA219 continuously measures current and voltage and transmits the values to the ATtiny via I²C. From this, the ATtiny calculates the other values and displays them on the OLED screen.
The I²C protocol implementation is based on a crude bitbanging method. It was specifically designed for the limited resources of ATtiny10 and ATtiny13, but it works with some other AVRs (including the ATtiny25/45/85) as well. The functions for the OLED are adapted to the SSD1306 OLED module, but they can easily be modified to be used for other modules. In order to save resources, only the basic functionalities which are needed for this application are implemented. For a detailed information on the working principle of the I²C OLED implementation visit TinyOLEDdemo.
The internal oscillator of the ATtiny is used to determine energy and capacity. The accuracy of the internal oscillator is +/-10% with the factory calibration. This can be improved to +/-2% or better by manual calibration. The calibration value determined in this way can be set in the source code.
Since there is no ICSP header on the board, you have to program the ATtiny either before soldering using an SOP adapter, or after soldering using an EEPROM clip. The AVR Programmer Adapter can help with this.
avrdude -c usbasp -p t85 -U lfuse:w:0x62:m -U hfuse:w:0xd5:m -U efuse:w:0xff:m -U flash:w:usb_tester.hex
|Voltage||3V - 12V|
|Voltage Measurement Resolution||4mV|
|Current Measurement Resolution||1mA|
This work is licensed under Creative Commons Attribution-ShareAlike 3.0 Unported License. (http://creativecommons.org/licenses/by-sa/3.0/)
|4||OLED 0.91||OLED||I2C OLED 0.91||1||SSD1306 I2C OLED|