Trinket Pro Multi-Readout Multimeter

This portable device gives a live read-out of current and voltage between your DC power source and your load! (max 26V DC, 3.2 A).

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This device uses an INA219, a Trinket 5v Pro, and a standard 16x2 LCD to measure the load voltage, shunt voltage, and current between a DC power source(26V ±3.2A Max) and its load . This enables real time monitoring of power draw!

UPDATE: upgraded to 20x4 LCD (because pretty)

In early 2013 I officially got into hobby robotics by helping Kickstart the BrickPi: a Raspberry Pi robotics platform. It has been a wonderful exploratory journey of programming, physical computing and electronics.

One of the most important parts about making a robot is power management. I wanted a reliable way to determine how much power was being consumed in real time when say, the robot was simply powered on, the robot was running its motors, the robot was live streaming video back to my desktop or simply taking in analog sensor readings.

I could have relied on the data sheets or used a multimeter twice (once in series for current then again in parallel for voltage), but I wanted to have a simple, accurate read out of both on a neat little LCD screen.When I first saw the Adafruit's INA219 breakout board I was sure I wanted to try it out and see of it could help me understand the power consumption of my robot (so that I could optimize the battery size, and reduce power consupmtion where ever I could).

I also realised that this device could be used to more accurately determine how much power was being delivered from a solar panel to a battery since the INA219 can measure current Bi-directionally.

Putting this all into a small form factor with a Trinket Pro with a battery and switch is the next challenge.

I also wanted to keep everything modular in case the INA219, Trinket, or LCD failed. You could also upgrade the LCD size from 16x2 to a 20x4 to read out things more clearly (will have to modify the contrast values).

(Future tests to do::: Do independant current measuring tests with both the INA219 and a multimeter for a standard load. Also put both current measuring devices in series for fun?)

  • 1 × 16x2 or 20x4 LCD Display
  • 1 × Adafruit INA219 Current Sensor Breakout Measure high side voltage and DC current draw over I2C. Be be sure to isntall the Adafruit library at
  • 1 × Adafruit Pro Trinket - 5V 16MHz
  • 1 × Protoboard Any small board used for permanent soldering will work
  • 50 × Male Header Pins

View all 14 components

  • Demo Videos

    John11712/29/2014 at 04:29 0 comments

    Here is a demo video of monitoring the power going from as USB cable to my phone:

    Here is a demo video of the power monitor showing the voltage/current within its own charging cable (whilst charging itself!):

  • Transfer to Protoboard

    John11712/23/2014 at 04:54 0 comments

    After getting the Trinket, LCD, and INA219 to work on a bread board I drew up everything on Fritzing so I had a reference should anything go wrong whilst transferring onto a permanent proto-board.

    I intentionally soldered on female pins so that:

    1. All components could be easily replaced should they fail.

    2. Components could be upgraded such as the LCD from size 16x2 to 20x4.

    3. I could remove and use the components for other concurrent projects to save money.

  • Transfer to Trinket and Reading out to LCD

    John11712/23/2014 at 04:47 0 comments

    29 NOV 14

    Modifying the Arduino code and moving around some input pins to get the LCD pins and INA219 to fit nicely onto the Trinket.

  • Proof of Concept

    John11712/22/2014 at 00:08 0 comments

    15 NOV 14

    I got the INA219 to give a Serial Readout of using an Arduino UNO thanks to the Adafruit Tutorial.

    I also got the UNO to readout the current and voltage onto a 16x2 LCD.

View all 4 project logs

  • 1
    Step 1

    Wiring up everything in a breadboard.

    Be sure to solder in the Lipo back pack of you want the rechargeable capability. Adafruit Guide can be found here:

    Also Solder on a switch to the lipo back pack for convenience:

    The Lipo back pack I chose was 1200mAh. This is a little over kill but can operate for about 19-20 hours.
  • 2
    Step 2

    Set up your Arduino IDE to load code onto your Trinket Pro. Adafruit's guide can be founde here:

    Also be sure to install the non-standard INA219 arduino library from git hub:

    more information for the INA219 can be found here:

  • 3
    Step 3

    Once everything works on a breadboard, think about how you want to transfer everything onto a permanent proto-board. Refer to my Project Log to see the orientation I chose. I recommend not destroying your breadboard wiring as it an invaluable troubleshooting reference if things go wrong during the transition to a proto-board.

    I recommend soldering on female headers on the proto board so that the components can get replaced should they fail, and the bulky LCD can be removed and assembled like lego to fit in your pocket.

    I also broke out four male pins on the INA219 to be V+, V-, and two GND pins. This will enable me to build specific cable adapters such as USB and barrel jack.

View all 5 instructions

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