My clothes dryer moisture sensor mechanism has failed so now I have to guess the time which typically results in wet clothes or over-dry clothes and wasted energy. The replacement part is not longer available, so instead of buying a new one and sending this one to the trash heap I thought I could solve the problem with an Arduino and some sensors.
I have the HH-4030 humidity sensor which can handle up to 185F, and from what I've determined so far, clothes dryers don't got much above 160F. I also have a ds1820 for the temperature.
Where I'm stumped is how to mount the sensors. The dryer exhaust duct is 4" flexible. There's about 6' from where it leaves the dryer and goes into the wall. Any holes I poke into the vent need to be somewhat airtight so it doesn't leak heat/moisture into the house.
At this point I'm looking for some feedback in terms of is this a feasible project and how could I safely and securely mount the sensors. Thanks
you could wire up to the existing sensor in the dryer. it will be two wires and wet clothes complete a circuit. all it does is sense resistance.
in you case, get a hard duct and some clamps. if you use a section of hard duct, you can tape or screw or bond your sensor.
I would suggest you get a metal box to add to the outside, mount that, then drill a pair of holes to let air move. do not bother with creating a scoop too draw air. humidity will travel at over 400 feet per minute and will keep the humidity in your box equal to the duct.
remember, the further away from the heat, the cooler the air and the higher the humidity.
Also be aware that modification or any works for that matter on mains connected devices without appropriate qualifications can lead to some very serious charges being laid against you in many countries.
Lots of great suggestions here! Based on some ideas here and materials available and local hardware store, my plan is to drill a few tiny holes in a 4" duct coupling, then build a tiny box from aluminum flashing to contain the sensor. I would then use worm drive clamps to attach the box to the coupling so that is is removable to maintain (clean lint from sensor etc.). And perhaps some silicone adhesive to make it air-tight as possible. I was also thinking of using insect screen (aluminum mesh) to keep the lint from contaminating the sensor instead of drilling holes. I've included a image of my parts list. Any feedback is appreciated.
bluejets:
Also be aware that modification or any works for that matter on mains connected devices without appropriate qualifications can lead to some very serious charges being laid against you in many countries.
hello just a thought why not make it wireless? and have the sensors inside the dryer?
a while back i tried putting my wireless nrf24l01 temp sensor node in the freezer and the walls of the freezer did not stop the signals, maybe it will work from inside a dryer too that is if the heat wont kill it.?
anyway just a thought.
interesting project so good luck man.
swe-dude:
hello just a thought why not make it wireless? and have the sensors inside the dryer?
a while back i tried putting my wireless nrf24l01 temp sensor node in the freezer and the walls of the freezer did not stop the signals, maybe it will work from inside a dryer too that is if the heat wont kill it.?
anyway just a thought.
interesting project so good luck man.
Inside would pose a lot of challenges.. how are you going to power it? will it tear up clothes? with the clothes tear it up? how to deal with heat (a lot hotter inside) and forces of spinning etc.
I completed the first pass at this solution. Will post photos later. Here are my initial observations:
Seems that the expensive humidity sensor may not be necessary. I should have thought about this more but it makes sense. Initially the energy from the heating coils is consumed by evaporation, which lowers the temperature (same effect as an evaporative cooler used in dry climates). As the clothes lose moisture, the humidity drops and the temperature rises. Initial testing suggests the clothes are dry around 90F. I was really expecting the temperatures to go higher. The sensor is about 3 feet from the dryer outlet. With no clothes in the dryer it will quickly go to 108F or higher.
The humidity sensor reacts much quicker than the thermistor, yet the RH% calculation requires temperature. Until it reaches a steady state things are a bit wonky. This makes sense since the themisto has a greater thermal mass. Thinking about swapping out for a lm35 or ds1820, if it's true they will react faster. More testing is needed here.
It's currently awkward to use as I need my notebook sitting on the washer (the cable just reaches) as I have no other solution to update the code and get the data. The sensor is mounted to the duct, so removal is tricky. I need the data (temp/rh% etc) to determine the calibration: what moisture values equate to dryness. Yet now I'm out of clothes to wash as I continue to make changes to the code. This will take some more iteration.
Initial goals are a buzzer (annoying I"m sure) and some sort of internet notification to notify of dry clothes. After that I'd like to stop the dryer. Currently I'm thinking of using the door open switch to stop the dryer, which seems like the safest method with a 240V device.
How to go wireless and be cost effective with Arduino? I could use a low power wireless, like xbee, but then I have to deal with all the fuss on the other end to receive. Instead, I'd rather have wifi on the device. The cost of the Arduino wifi is just too high. I'd sooner buy another rasp pi and wire it up to the Arduino.
rappa:
After that I'd like to stop the dryer. Currently I'm thinking of using the door open switch to stop the dryer, which seems like the safest method with a 240V device.
TomGeorge:
Hi, where was the original sensor located?
Tom.....
Good question. I don't know. I did remove some of the panels off the dryer but did not see it. I'd guess it's in the back of the drum. From reading the support forums, it's not the sensor that dies, it's the circuit board that senses it, and that was not longer available, although I found a reseller selling one for $100. At that price though it's not worth it for such and old appliance.
Chart of humidity/temp. I need to update the sketch to take several readings and average. Currently it's only one reading per data point so a bit jumpy
Interesting graphs. What is that knee in the temperature chart where it suddenly drops? Did you turn off the dryer at that point?
And are the units correct? Did it really only take 5 seconds for the humidity to drop like that? Or is it really seconds, not milliseconds, and it took 90 minutes?
A low pass digital filter, or a simple sliding window average should clean up that humidity data nicely.
I notice that the ripple in the humidity has a similar period to the ripples in the initial curve of the temperature. Does that correlate to the heat source (gas burner?) cycling on and off to maintain temperature?
Yes, I turned off the dryer right where the temp starts to drop and x-axis is seconds, not ms. Yeah, the humidity is pretty consistent up/down so the heater coil cycle seems a likely explanation. It's an electric dryer. I'll work on smoothing the data and run again
rappa:
I'll work on smoothing the data and run again
How are you generating the graphs? Do you have all of the data from that run captured? I'd put it in a spreadsheet and play with a few smoothing algorithms, comparing them to the unsmoothed data, to see which gives you a good result without skewing the data too much. Then fold that back into your sketch and collect more data. Much faster and easier than waiting another 90 minutes for a complete cycle.
ShapeShifter:
How are you generating the graphs? Do you have all of the data from that run captured? I'd put it in a spreadsheet and play with a few smoothing algorithms, comparing them to the unsmoothed data, to see which gives you a good result without skewing the data too much. Then fold that back into your sketch and collect more data. Much faster and easier than waiting another 90 minutes for a complete cycle.
I have the Arduino sending data every 15 seconds. Then I upload the csv to google spreadsheets to create the chart. I'll fine tune the process on the next run
