Monitoring Sensors and Taking Action

I recently wrote a blog around using Microshift to run my Zigbee2MQTT workload. This blog described all the details on how to deploy Microshift and then deploy the components inside of Microshift to enable some home automation. Of course with Zigbee2MQTT there is an intuitive web interface to interact with the smart devices. However I wanted to take another approach that felt more realistic when it comes to edge use cases. I felt that in a industrial scenario there would be some code that would most likely subscribed and monitoring the MQTT queue. An action would be performed when a certain event was observed and the action itself might publish something into the MQTT queue. The rest of this blog will cover a simple scenario like I just described.

First we continue to use the same lab environment I used in my previous blog. The only difference here in the diagram below is we have now added a smart power outlet and a temperature/humidity sensor that can both be controlled remotely via the Zigbee protocol like all my other devices.

The Script

With my lab in place I decided I wanted ot write something in Perl. Some might think why use such an antiquated language like Perl and part of that is because I am old school. For my scenario I envisioned using the humidity sensor to detect when the humidity levels got too high. The threshold would then trigger an action on the event to turn on/off a dehumidifier plugged into the smart outlet. The basic process flow looks like the following diagram:

The script itself can take four different parameters:

• --hostname: hostname or IP address of MQTT host (required)
• --port: port for MQTT (optional but will default to 1883 if not provided)
• --threshold: humidity value that determines when action should be taken
• --help: prints the usage of script

The script itself is located here

When one runs the script without any flags the usage and an example will be displayed.

./mqtt-humidity.pl 
Usage:
      --hostname,-h   Hostname or IP address of MQTT host
      --port,-p       Port for MQTT (defaults to default 1883)
      --threshold,-t  Threshold for humidity (defaults to 60)
      --help,-h       Print this help

    Example:

    mqtt-humidity.pl -ho 10.43.26.170 -p 1883 -t 65

The Demonstration of Script

To demonstrate this script I went ahead and plugged in a light into my smart outlet which was in the off setting. I launched the script in a terminal window. Then I took the temperature/humidity sensor, cupped it in my hands and blew into my hands. The moisture in my breath is enough to temporarily raise the value. The script provides output so we can see the values changing and sure enough when I breathed into my hands with the sensor the value jumped to 81.37% which triggered the action event and turned on the light. I then set the sensor back on my desk and over the course of 5 minutes the value slowly receded. Once it dropped below the threshold value the light then turned back off. The output of my script run is below:

$ perl mqtt-humidity.pl -ho 10.43.26.170 -p 1883 -t 60
Temp C = 23.43 : Temp F = 74.174 : Humidity = 51.22
Temp C = 23.43 : Temp F = 74.174 : Humidity = 81.37 <-- Smart outlet turned on
Temp C = 23.43 : Temp F = 74.174 : Humidity = 84.37
Temp C = 23.43 : Temp F = 74.174 : Humidity = 82.37
Temp C = 23.43 : Temp F = 74.174 : Humidity = 80.28
Temp C = 23.43 : Temp F = 74.174 : Humidity = 78.79
Temp C = 23.63 : Temp F = 74.534 : Humidity = 78.79
Temp C = 23.63 : Temp F = 74.534 : Humidity = 73.21
Temp C = 23.63 : Temp F = 74.534 : Humidity = 74.34
Temp C = 23.63 : Temp F = 74.534 : Humidity = 72.91
Temp C = 23.63 : Temp F = 74.534 : Humidity = 71.65
Temp C = 23.63 : Temp F = 74.534 : Humidity = 70.55
Temp C = 23.63 : Temp F = 74.534 : Humidity = 69.15
Temp C = 23.63 : Temp F = 74.534 : Humidity = 67.93
Temp C = 23.63 : Temp F = 74.534 : Humidity = 66.57
Temp C = 23.63 : Temp F = 74.534 : Humidity = 64.87
Temp C = 23.63 : Temp F = 74.534 : Humidity = 63.28
Temp C = 23.63 : Temp F = 74.534 : Humidity = 62.08
Temp C = 23.63 : Temp F = 74.534 : Humidity = 60.71 
Temp C = 23.63 : Temp F = 74.534 : Humidity = 59.12 <-- Smart outlet turned off
Temp C = 23.63 : Temp F = 74.534 : Humidity = 57.72
Temp C = 23.63 : Temp F = 74.534 : Humidity = 56.7
Temp C = 23.63 : Temp F = 74.534 : Humidity = 55.6
Temp C = 23.63 : Temp F = 74.534 : Humidity = 54.23
Temp C = 23.63 : Temp F = 74.534 : Humidity = 53.21
Temp C = 23.63 : Temp F = 74.534 : Humidity = 52.14
Temp C = 23.63 : Temp F = 74.534 : Humidity = 51.05
Temp C = 23.63 : Temp F = 74.534 : Humidity = 50.04
Temp C = 23.22 : Temp F = 73.796 : Humidity = 50.04
Temp C = 23.22 : Temp F = 73.796 : Humidity = 50.04
^C

Now this was a very simple example but imagine the possibilities. For example what if this was a greenhouse that needed to keep the humidity and/or even the temperature at a certain range. If the device that reduces the humidity/temperature (dehumidifier -or- exhaust fan) in the greenhouse could take Zigbee commands directly and control the speed of operation we might be able to not only turn it on/off but also increase/decrease speed of operation. All of this ensures that whatever was growing in the greenhouse is not damaged and also ensures we are powering devices only when we need to have them powered. The bottom line is it saves businesses like the greenhouse operational costs when they are operating efficiently.

Alternate Appliance Troubleshooting

 

Normally I would not document about an appliance problem.  After all I have replaced quite a few components across a wide array of appliances including a stop clutch in a Whirlpool washing machine.  However this latest experience was one that I felt needed better documentation given that the symptoms can sometimes be confused with those of other components and one might replace those first which can lead to a lot of extra cost without results.  Before we dive into the symptoms and fix though, lets introduce the appliance in question.  In my case it was a Whirlpool Gold Series Dishwasher (WDF750SAYM3) however the following will most likely apply to any Whirlpool dishwasher.

The problem started a few months ago with a undissolved soap packet after a completed cycle.  I didn't think much of it and carried on.  However then on another cycle I never heard the water spraying inside the dishwasher.   The washer would fill and drain but never engage the spraying of the water to actually wash the dishes.   At this point I was starting to wonder what was going on so I did a little research and found how to do a diagnostic run cycle on the dishwasher.  This involved by pressing any 3 (three) keys in the 1-2-3-1-2-3-1-2-3 sequence except Start, Delay,  or Cancel  and making sure the delay between key presses is not more than 1 sec.  If a problem is found, the dishwasher may display an error code by flashing the clean button in two sequences.  The first sequence will flash the clean led multiple times and then pause and the second sequence will flash clean led multiple times.  By counting the flashes in both sequences I would get a two digit error code.  However upon running the diagnostics I only got a code showing the water was too cold which makes sense because the run from my hot water heater is quite far and unless I run the hot water at the sink the initial water will be cool. With the diagnostics not showing any issues I started to try to find an answer online.  Most of the information found though seemed to point to a bad spray pump or a controller board issue.   I did not think it was either of these those because on some days the dishwasher worked normally without any problems but then on other days it seemed more problematic.  That was when I stumbled across a post where it was indicated that on this particular model of Whirlpool dishwasher there was a bad latch design and the latch mechanism had no test in diagnostic mode.  I thought I might be onto something so I replaced the latch with a new redesigned part.  The dishwasher seemed to be working.

The success however was short lived and if anything I was seeing the pattern of failures starting to become more prevalent.  In observing the dishwasher I found that a run would fail if during the first fill the spraying action did not start before the water shutoff.  So I would hit Cancel and Start again and sometimes it would eventually work.   I also found that if the water was hot on the start the chances of a successful wash went up.  Again when the dishwasher would work it was just fine so I still was ruling out it was a spray pump issue or controller board issue.  If either were truly bad I would expect my dishes to come out dirty and when the dishwasher worked they were clean.

Again I went back to researching on the internet and came across a conversation about the turbidity sensor (sometimes referred to as OWI) in Whirlpool dishwashers.  So what does this sensor do?  As the soil level increases, the amount of transmitted light decreases. The turbidity sensor measures the amount of transmitted light to determine the turbidity of the wash water. These turbidity measurements are supplied to the dishwasher controller board, which makes decisions on how long to wash in all the cycles.  However this is only part of the story because this sensor also has a thermistor built into it as well which monitors water temperature.  The temperature monitoring is key because as I stated earlier my dishwasher seemed to have better success when the water was very hot coming into the dishwasher.

With my new found information I proceeded to test my turbidity sensor.  With the power supply to the dishwasher turned off, the turbidity sensor can be tested from the main controller board at the connection P12 from the wire at pin 1 to the wire at pin 3. The resistance should measure between 46KO to 52KO at room temperature.  My resistance however was not in specification so I knew I found the source of my problem.

I went ahead and ordered my replacement sensor and when it arrived I used the following video to guide me through replacing the sensor:

Once the sensor was replaced I needed to run another diagnostic since that is what Whirlpool recommends when replacing the turbidity sensor.  Once that was complete I tested out the dishwasher over the course of a few days running multiple loads per day.   Every cycle was successful so I could finally declare success.   I should note however that when I was replacing the sensor I noticed my water supply line was corroded and slightly leaking but I will save that story for another day.