SEN-12040 - SparkFun Electronics - Datasheet.Directory

INA169 Breakout Board Hookup Guide

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CONTRIBUTORS: SHAWNHYMEL

Introduction

Have a project where you want to measure the current draw? Need to

carefully monitor low current through an LED? The INA169 is the chip for

you!

The INA169 is a “high-side current monitor,” which means that you place a

resistor (a “shunt resistor”) on the positive power rail and the INA169

measures the voltage drop across that resistor. The INA169 outputs a small

current based on the measured voltage drop. If you place a resistor from

the output of the INA169 to ground, you can measure the voltage at the

output. With some basic math, the output voltage gives you the current

through the shunt resistor.

Covered In This Tutorial

In this tutorial, we cover how the board should be used. The Board

Overview section covers some theory and math on how the current sensing

works, so feel free to skip to the Hookup Example if you just want to see the

board in action. The Hookup Example shows how to connect the board to

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an Arduino in order to measure the current through an LED, and the

Example Code provides a quick Arduino sketch for displaying the measured

current to the Serial Monitor.

Required Materials

• Arduino, RedBoard or any Arduino-compatible board.

• Male headers to solder to the board and make it breadboard

compatible.

• Jumper wires to connect from breadboard to Arduino.

• Breadboard to tie everything together.

• Basic Red LED so we have something to light up.

•330Ω Resistor to limit the current through the LED.

Suggested Reading

• Voltage, Current, Resistance, and Ohm’s Law

•Resistors

•LEDs

• How to Use a Breadboard

• What is an Arduino?

• How to Solder

• Working with Wire

Board Overview

Take a look at the schematic, and you will notice that the breakout board

consists of a shunt resistor (R ), the INA169 chip, and an output resistor

(R ). While R and R might appear to have 2 resistors, only one is

populated on the board. If you would like to change the values of the

resistors, you can replace them or put another resistor in parallel.

LSL

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INA169 Current Sensing Breakout Schematic

As current passes from V through R to V , it creates a current drop

across R . The op-amp inside of the INA169 chip measures the difference

between the V and V voltages and outputs a voltage based on that

difference. The output of the op-amp is amplified through the internal

transistor, which sources a current out of the INA169 chip. As that current

passes through R to ground, a voltage level is generated at V .

IMPORTANT: The INA169 is configured to measure DC only. The VIN+ pin

must be at a higher potential than the VIN- pin, which means that the

INA169 cannot measure AC.

Measuring Current

The voltage at V can be measured using an oscilloscope or an analog-

to-digital converter. A bit of math is needed to convert to the source current

(I ):

Iis the current we want to measure.

Vis the voltage we measured at the output of the INA169.

1kΩis a constant resistance value we need to include due to the internals

of the INA169.

Ris the value of the shunt resistor. If you do not modify the board, then

this is set at 10Ω.

Ris the value of the output resistor. If you do not modify the board, then

this is set at 10kΩ.

IN+ S IN-

IN+ IN-

LOUT

OUT

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Example

For example, let’s say that you hook up the board and you measure 2.8V at

V . Plugging this into our equation, we would get:

This shows that you have 0.028A (or 28mA) flowing through your line.

The Pinout

There are only 5 pins on the breakout board.

GND should be connected to ground of the circuit you are trying to measure

VIN+ needs to be connected to the positive side of the source (e.g. battery,

output pin, etc.)

VIN- needs to be connected to the positive side of the load (e.g. VCC on

Arduino, positive side of an LED, etc.)

VOUT is the measured output and should be connected to something that

measures voltage levels, such as a multimeter, oscilloscope, or an Arduino

ADC pin

VCC is the supply power to the INA169, which needs to be connected to

3.3V, 5V, etc. This can be anywhere from 0 to 75V. Note that the V

range depends on the voltage supplied by VCC.

In addition to the pins on VIN+ and VIN-, the board also has two large pads

around R , which are capable of taking alligator clips should you want to

have a temporary hookup. Note that GND and VCC will still need to be

connected for the board to function.

Modifying Functionality

OUT

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The INA169 cannot sense any differences across R greater than 500mV,

and the output error increases once the voltage across R dips below

35mV. If you include the voltage drop across the internal transistor, this

means that the default setup of the breakout board is limited to measuring a

current range of about 3.5mA to 35mA.

If you would like to change that range, R and R can be replaced with

resistors of different values. R can be removed and replaced with another

resistor fairly easily. R is a bit more difficult as it is a small, surface mount

resistor. Changing either of the resistors changes the equation from above.

With R at 10kΩ, changing R gives us the following ranges:

R Current Sense Range

10Ω3.5mA - 35mA

1Ω35mA - 350mA

0.1Ω350mA - 3.5A

IMPORTANT: Be careful with the power rating on the resistor! If you

choose a 0.1Ω resistor for R and expect to see 3.5A through it, this can

result in 1.2W of heat being generated - way too much for your average

¼W resistor! You will need a resistor that can handle at least 2W. The

following power resistors are recommended:

•Ohmite 1Ω 1% 3W

• Ohmite 0.1Ω 1% 3W

Hookup Example

Assembly

You will need to solder either wires or straight male headers to the 5 header

holes on the board. If you need to measure over 35mA, you will need to

desolder the RS resistor and solder a lower value (e.g. 1Ω), higher power

(e.g. 3W) resistor to the holes around RS.

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Headers are optional but recommended if you are using a breadboard.

Connecting the INA169 Breakout Board

Fritzing of the INA169 connected to an Arduino

As shown in the diagram, connect the Arduino 5V to the INA169 VCC and

the Arduino GND to the INA169 GND. To read the output voltage level, we

need to run a jumper cable from the Arduino A0 to the INA169 VOUT pin.

Use a jumper wire to connect the INA169 VCC and VIN+ pins, as we want

to power the LED with the Arduino 5V. If you use a different power source

(other than the Arduino 5V or 3.3V) through VIN+ and VIN-, make sure you

connect the ground of the power source to the ground of the INA169 board.

Just ensure that the voltage level as measured from VIN+ to ground does

not exceed 60V. Bad things will happen to the board if you do.

Connect a 330Ω resistor from the INA169 VIN- to the anode of the LED and

a jumper wire from the LED’s cathode to GND.

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Actual circuit example

If you want to measure the current going to something else, you can use

alligator clips on the bare metal pads around RS. Make sure that the

INA169 board is inline with the positive power rail and that the INA169 GND

is connected to the target’s GND.

Example Code

Open the Arduino program and paste the following code into the sketch:

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11142013

SparkFun Electronics 2013

Shawn Hymel

This code is public domain but you buy me a beer if you use t

his

and we meet someday (Beerware license).

Description:

This sketch shows how to use the SparkFun INA169 Breakout

Board. As current passes through the shunt resistor (Rs), a

voltage is generated at the Vout pin. Use an analog read and

some math to determine the current. The current value is

displayed through the Serial Monitor.

Hardware connections:

Uno Pin INA169 Board Function

+5V VCC Power supply

GND GND Ground

A0 VOUT Analog voltage measurement

VIN+ and VIN need to be connected inline with the positive

DC power rail of a load (e.g. an Arduino, an LED, etc.).

// Constants

const int SENSOR_PIN = A0; // Input pin for measuring Vout

const int RS = 10; // Shunt resistor value (in ohms)

const int VOLTAGE_REF = 5; // Reference voltage for analog re

// Global Variables

float sensorValue; // Variable to store value from analog re

float current; // Calculated current value

void setup() {

// Initialize serial monitor

Serial.begin(9600);

}

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void loop() {

// Read a value from the INA169 board

sensorValue = analogRead(SENSOR_PIN);

// Remap the ADC value into a voltage number (5V reference)

sensorValue = (sensorValue * VOLTAGE_REF) / 1023;

// Follow the equation given by the INA169 datasheet to

// determine the current flowing through RS. Assume RL = 10k

// Is = (Vout x 1k) / (RS x RL)

current = sensorValue / (10 * RS);

// Output value (in amps) to the serial monitor to 3 decimal

// places

Serial.print(current, 3);

Serial.println(" A");

// Delay program for a few milliseconds

delay(500);

}

Plug in the Arduino and upload the code. You should see the LED light up

as soon as you apply power.

The INA169 will measure the current through the LED.

Select the appropriate board (Arduino Uno in this case) from Tools->Board

and the correct COM port from Tools->Serial Port. Click the upload button,

and wait for the program to be compiled and uploaded to the Arduino. Open

the Serial Monitor from Tools->Serial Monitor and you should see current

measurements being printed.

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If you are using a basic red LED, a 330Ω resistor, and a 5V supply, you

should see 0.009A (9mA) on the Serial Monitor.

If we want to verify this reading, we can use a multimeter to measure the

voltage across the 330Ω resistor. You should see around 3V across the

resistor. Using Ohm’s Law, we can calculate the current flowing through the

resistor and LED is 0.00909 A, which matches the reading from the

INA169.

Going Further

The INA169 is a useful chip if you want to know how much current

something is using. For example:

• On The Uncertain 7-Cube, you can connect the INA169 inline with

the battery’s positive power wire (that’s the red wire!) and measure

the current draw to figure out how long your battery will last.

• Similarly, connect the INA169 to the HUB-ee Buggy’s power and

determine how much time you get before you need to replace those

AA batteries.

• Or use the INA169 to determine how much power is being consumed

if the Humidor Control Box is left on all the time.

Resources

• INA169 Datasheet

• Breakout Board Schematic

• Eagle and Project Files

• GitHub Repository

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