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  • Author Author: tariq.ahmad
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Using Nordic's nRF7002, My Dehumidifier Tells Me When It's Full! -- Episode-650

Many appliances need a human’s attention to perform maintenance actions. For example, James's lab dehumidifier turns on an LED to indicate its reservoir is full. Wouldn’t it be nice if it could use the Internet to notify someone it needs emptying? With the help of Nordic’s nRF7002 Design Kit (DK), it is now possible to get a phone notification when an LED turns on. 

Watch the Video:

Project Overview 

James reviewed Nordic’s nRF7002 design tools in another video. The nRF70 is a dual-band Wi-Fi 6 companion IC for microcontrollers (MCUs.) He planned to use the QFN-packaged chip in a custom printed circuit board (PCB). However, things do not always go as planned. 

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Initially, James used the nRF7002 Design Kit (DK) board. This board has the nRF70 and chip antennas for both bands. It also features an nRF5340 application processor connected to the nRF70. The board has various header pins, breakout points, and other useful debug features. For example, it has a third chip, which is another MCU. However, that MCU is dedicated to programming and debugging the application processor.  

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Nordic’s nRF SDK Connect is based on the Zephyr real-time operating system. There is an example for the nRF7002 DK that connects to an MQTT broker and sends a message once per minute. James modified that example to read for an analog-to-digital converter (ADC) input and send that value to the broker. Feeling confident about his new Zephyr skills, James tried changing microcontrollers. 

Xiao + nRF7002 

Since this project really only needs a single analog input, the Seeed Studio Xiao BLE seemed like a perfect choice. It has a Nordic microcontroller and just enough I/O pins to connect to an nRF7002. After spending some time modifying the Zephyr Devicetree and reconfiguring a blink project for the Xiao, James had a blinking LED. 

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However, that’s when James discovered a significant mistake with the design! 

The Xiao’s microcontroller is Nordic’s nRF52840. This chip only has a single core and 256 kilobytes of RAM. The nRF53 on the  nRF7002 DK has a dual-core processor with their own RAM. The chip dedicates one core to the user application and (optionally) the other core to managing network operations. The application processor has twice the RAM of the nRF52! 

This difference is significant because the MQTT example needs almost 250 kilobytes of RAM! In other words, there isn’t enough memory to run the code on the Xiao BLE! 

Back-Up Plan 

Since James really wanted a Wi-Fi LED Detector, he decided to go another route. He built the project around the design kit instead of his custom PCB. After all, the fundamental code was already in place!  

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The first step was to solder the photoresistor to the DK board. Next, James installed it into a 3D-printed case. A few measurements and tests then demonstrated that detecting whether the dehumidifier’s FULL light was ON or OFF was possible. 

With the hardware working, James used a Nordic Power Profiler Kit 2 to see how much energy a Wi-Fi LED Detector would consume on average. The answer? About 4.25 milliamps!  

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That number is really high for an IoT device. However, it is very good for an IoT device based on a design kit and with ZERO code optimizations–like sleep modes. So, James decided to just wrap up this stage of the project here. 

RF Measurements 

A lesson James learned is that he should have studied the code examples more before designing a custom PCB. Even though the custom board wouldn’t work how he needed it, James still wondered what the RF path looked like.  

Using a Vector Network Analyzer (VNA), James measured the response of the dual-band antenna. It looks good for the 2.4 GHz Wi-Fi bands. However, James is concerned that the response is a bit weak for the 5 GHz bands.  

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Regardless, it still looked good on the VNA for a first try! 

Downloads & Links:

Bill of Material:

Product Name Manufacturer Quantity Buy Kit
nRF7002, RF Transceiver, 2.401 GHz to 5.895 GHz, 86 Mbps,-98.6 dBm , 21 dBm Pout, 2.9V to 4.5Vsupply, QFN-48 Nordic Semiconductor 1 Buy Now
nRF7002-EK, Evaluation Kit (Shield Style) Nordic Semiconductor 1 Buy Now
nRF7002-DK, Design Kit Nordic Semiconductor 1 Buy Now
nRF7002-EB, Evaluation Board Nordic Semiconductor 1 Buy Now
nRF52840 Xiao (BLE) Seeed Studio 1 Buy Now
 
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  • Nice project.

    I appreciate your sharing your issues, it helps us decide to try to use the boards.

    Good job.

  • Perhaps this idea could be expanded into a diagnostics tool for larger systems. I often find myself faced with intermittent system faults where having a time-stamped log of status of a number of LEDs would be very useful. It's not uncommon to have 50+ status LED's involved for a relatively simple set up.

    Also the ability to control camera capture of more advanced displays to be able to save and timestamp the +/- 60s of activity when a certain event occurred. 

    As components of systems can be quite spread out, then leveraging an existing network infrastructure using IOT monitoring devices could simplify the set up.

    One of the challenges might be to get the numerous sensors to attach in front of the LEDs as some may be on a front panel, some on a rear panel, some on curved surfaces, some built into RJ45 jacks populated with cables and so on. Also more and more status LEDs these days are multicolour and have different flash patterns to indicate a fault condition so some on-device sensor decoding may be required to detect the fault status. Similar applies to more advanced readouts where it may be an error codes displayed on a 7-seg readout or specific symbols appearing on a LCD panel, which may or may not be cycling through different status pages.

  • in reply to BigG

    If I had used something with an nRF53, this project would have gone how I expected. But that is entirely because of my inexperience with Zephyr.

    Nordic does seem all-in on Zephyr compared to other microcontroller manufacturers. Most have some support, but it's almost like an afterthought. Nearly all of Nordic's SDK is built around it. (Or it seems that way to me.)

    I don't know what Esspresif's support for Zephyr is like (yet). But with their popularity, I would expect it to be decent.

  • Oh rats! I have a dehumidifier that regularly gets full (it's damp around these parts). I also have Xiao boards (lot's of them) and recently I've been tinkering with Zephyr. So you can guess what my next project start will be...

    However, as I don't have a nRF7002 EVB, I think I'm going to try this out using the Xiao ESP32 S3. It will be interesting to see how far I get here as I know Nordic Semiconductor have put in a decent amount of effort into getting their boards to work with Zephyr and their documentation is pretty good. I've not had the same luck with other boards but then again, I haven't had a project as good as this one.

  • ROFL - feature expansion.

    My basement dehumidifer gets turned off by the cats because they use it as step to get on top of a nearby chest freezer. The power button is on the top. 

    Sure would be nice to know if its available to run. Not only do I have to check for for a full tank, but also if its been accidentally turned off.  :-)

  • In the video, I made the comment that I didn't want to wait a few hours.

    The weather hasn't shifted enough yet. Since shooting the demo (about a month ago), it hasn't run enough to even fill 10%.

    That will change next month...

  • in reply to dougw

    In the summer, even with the dehumidifier running, there's enough humidity to keep ESD a non-concern.

    In the winter, however, I wear ESD straps!

  • Good application - my lab in my basement has a dehumidifier.

    Our lab at work, on the other hand, needs a humidifier to minimize ESD.