31-01-2016, 10:33 PM
What other sensors does this machine have? Not much, in all honesty. There's another NTC - this time it's in the outlet from the drum, so it's sampling the temperature of the moist air that has just passed through the clothes. I expected to find some sort of humidity sensor in this location, but no such luck. Hmmm...
Apart from the door sensor and the float switch that tells the micro to turn on the condensate lift pump (and pause the program and light the red "empty me" LED when it's full), I couldn't find anything else. So given a lack of a logical plan, I started taking the machine apart a bit more. The lower front panel came away fairly easily, and I took the opportunity to clean up the airways properly. But nothing really doing...
Then I stuck my head inside the drum. Using a torch, I don't know what I was expecting to see, but I noted that there is a section - just inside the door - that is separate from the other plastic mouldings behind the front panel. Wonder why? This section of plastic has two stainless steel strips, but these look for all the world like they're simply there to have less friction than the plastic - but I wasn't wholly convinced!
So upon undoing 3 screws, off it came, complete with 3 wires attached via "faston" connectors to these metal strips!
For a picture, the item in question is here: http://www.amazon.co.uk/Bracket-Sensor-W...B00GCFRYJM
Now, this was the missing link in the puzzle. With no obvious humidity sensor, how was the machine telling when clothes were dry? OK, perhaps you can get so much from the temperature sensors, and presumably these change as the drying proceeds, but now we have something that is clearly able to detect when wet clothes are touching the front of the drum.
As far as the reverse-engineering had gone, I still hadn't worked out what the second control box was doing. As mentioned, it gets mains. There's only 2 other connectors - each with a pair of wires. One pair went to the main controller, and was the transistor side of an opto-coupler, which obviously finds its way into a port of the micro. But the other pair disappeared down the front of the machine, along with the wiring to the motor, and my working theory was that this might have been some sort of feedback from the motor (pulse counting, perhaps?), simply because I had no better ideas! But no - these unidentified wires went to these metal contacts inside the drum.
This makes sense. The main control box is actually live - the PSU doesn't isolate. But the second control box has a tiny mains transformer (plus the opto-isolator to abstract it from the main control circuit). So someone can safely touch the metal strips just inside the door with no issues. I didn't reverse-engineer the whole circuit, but that fits.
Apart from the door sensor and the float switch that tells the micro to turn on the condensate lift pump (and pause the program and light the red "empty me" LED when it's full), I couldn't find anything else. So given a lack of a logical plan, I started taking the machine apart a bit more. The lower front panel came away fairly easily, and I took the opportunity to clean up the airways properly. But nothing really doing...
Then I stuck my head inside the drum. Using a torch, I don't know what I was expecting to see, but I noted that there is a section - just inside the door - that is separate from the other plastic mouldings behind the front panel. Wonder why? This section of plastic has two stainless steel strips, but these look for all the world like they're simply there to have less friction than the plastic - but I wasn't wholly convinced!
So upon undoing 3 screws, off it came, complete with 3 wires attached via "faston" connectors to these metal strips!
For a picture, the item in question is here: http://www.amazon.co.uk/Bracket-Sensor-W...B00GCFRYJM
Now, this was the missing link in the puzzle. With no obvious humidity sensor, how was the machine telling when clothes were dry? OK, perhaps you can get so much from the temperature sensors, and presumably these change as the drying proceeds, but now we have something that is clearly able to detect when wet clothes are touching the front of the drum.
As far as the reverse-engineering had gone, I still hadn't worked out what the second control box was doing. As mentioned, it gets mains. There's only 2 other connectors - each with a pair of wires. One pair went to the main controller, and was the transistor side of an opto-coupler, which obviously finds its way into a port of the micro. But the other pair disappeared down the front of the machine, along with the wiring to the motor, and my working theory was that this might have been some sort of feedback from the motor (pulse counting, perhaps?), simply because I had no better ideas! But no - these unidentified wires went to these metal contacts inside the drum.
This makes sense. The main control box is actually live - the PSU doesn't isolate. But the second control box has a tiny mains transformer (plus the opto-isolator to abstract it from the main control circuit). So someone can safely touch the metal strips just inside the door with no issues. I didn't reverse-engineer the whole circuit, but that fits.
