How to Properly Measure the Current of ESP32 Devices

The energy consumption of a device is especially important when those devices are Internet of Things (IoT) devices. This fact applies to devices running ESP32 hardware as well.

However, you cannot just simply measure the current of an ESP32 device by connecting it to an oscilloscope or anmeter of your choice. If you are not careful, you may even risk damaging the device.

To the best of my knowledge, there are not many resources that explain how to properly measure the current of ESP32 microcontrollers.

In this guide, I would like to share what I learned in the process of measuring the energy usage of my own ESP32 devices and common pitfalls to avoid.

Choosing the Right Measurement Tool

You can measure the current of an ESP32 device using an oscilloscope. However, doing so is challenging, since oscilloscopes measure voltage, not current. To do so, you will need to indirectly measure the current by measuring the voltage drop of the device. Even then, you may not even get fully accurate measurements when your ESP32 device is operating at really low currents, such as during deep sleep, due to noise.

Oscilloscope are not designed for this task. They are really good at measuring voltage at really low timescales (e.g. in the range of micro- or nanoseconds), but they are not good at measuring voltage when the voltages are really small (e.g. in the range of microvolts). As a result, obtaining the current through the voltage drop measured by an oscilloscope will not get us far.

To measure currents, especially really low currents, we will need to look for other tools. To find these tools, we need not look further than the ESP-IDF Programming Guide:

Therefore, an ammeter suitable for measuring current in Deep-sleep mode should have low internal resistance and, ideally, switch current ranges dynamically. We recommend two options: the Joulescope ammeter and the Power Profiler Kit II from Nordic.

In this tutorial, I will be using the Nordic Power Profiler Kit II (PPK2).

How to Not Measure Low Currents

You can set up an ESP32-H2 with the PPK2 by using jumper wires to connect:

• the VCC port of the PPK2 to the 5V0 ² pin of the ESP32 device, and
• the GND port of the PPK2 to the GND pin on the ESP32.

In this configuration, you can use the PPK2 to measure the current of the ESP32-H2 while the PPK2 itself is providing 5V of power. This is how I initially approached the measurement of my ESP32-H2 device.

However, this approach will not work when the ESP32-H2 is consuming really low currents in the uA range: the PPK2 will report much higher currents than expected.

When measuring the deep sleep current of my ESP32-H2 when it ran the ESP32 OpenThread boilerplate deep sleep SED program, the PPK2 reported a current of ~1.21 mA, when it should have instead measured the current at ~7 uA, the expected value of the deep sleep current for an ESP32-H2 ³.

The J5 Header

These inaccurate low current measurements occur when the J5 header jumper of the ESP32-H2 has not been removed.

In order to accurately measure the current of an ESP32-H2, the J5 jumper will need to be removed ⁵ from the ESP32-H2 for the duration in which the PPK2 is measuring the current of the device.

Measuring Small Currents Correctly

To properly measure low currents using the PPK2, we will need the following setup:

• Connect the VCC port of the PPK2 to the 3V3⁶ pin of the ESP32-H2, or to one of the two J5 pins that are visible when the J5 jumper has been removed.

• Connect the GND port of the PPK2 to the GND pin of the ESP32-H2.

Set the PPK2 to provide 3.3V of power to the ESP32-H2. Do not set the PPK2 to provide 5V of power, as doing so can damage the device. After following these steps, the PPK2 will be able to accurately measure low currents.

Helpful Resources

In this section, I compile the helpful resources that I used when I was in the process of figuring out how to properly measure the low currents of my ESP32-H2s during deep sleep with the PPK2.

• The ESP32-H2 Devkit Documentation, particularly the section about the J5 header.

• The conversation I had with Espressif engineer Sprite in the ESP32 forums about the purpose of the J5 header. I want to thank Sprite for taking the time to teach me about the J5 header.

• The Current Consumption Measurement of Modules page in the ESP-IDF Programming Guide. This webpage describes the tools recommended by Espressif to measure the current of ESP32 devices, along with discussing the general approach to measuring the current of such devices.

• The conversation I had in the Digilent forums when I was figuring out how I could accurately measure the deep sleep current of an ESP32-H2 using the Analog Discovery 3. I would like to thank Digilent engineers JColvin and attila for teaching me how to use the AD3 with the Current & Power Adapter to measure the current of my ESP32-H2 devkit.

• The PPK2 video review by Circuit Digest on YouTube. The video review contained a short tutorial on how to set up the PPK2 with an ESP32 device. Although the ESP32 device used in the video was different than the ESP32-H2, I found the video helpful nonetheless when initially measuring my ESP32-H2 with the PPK2 with 5V of power (before I learned about the J5 header).