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Faking a fan feedback signal

AlboGator

1,407 views

I had a Samsung fdbm refrigerator where the week before christmas I got a no cool complaint. Checking the part, it had to be shipped in. It arrived that Friday, and of course it was the wrong evap cover. I devised a plan, but thankfully didn't have to use it. In the end I was able to swap the fan motors and use the existing evap cover but just for fun I garaged a proof of concept using a simple voltage divider circuit. 

What it does is take the I put to the fan, and divides it into a lower voltage to tap into and feed back. The output voltage is dependent on the input voltage. It took a bit of playing with to get it right, but it would have worked. 

This was the only time I've seen this happen btw. 

 



8 Comments


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Samurai Appliance Repair Man

Posted

Pretty awesome hack and a nice demo of tricking out the microprocessor looking for a missing RPM signal. Thanks for posting this!

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On 2/17/2017 at 1:00 AM, Samurai Appliance Repair Man said:

Thanks for posting this!

Experiments are fun. Was wondering "This thing on", lol. 

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Samurai Appliance Repair Man

Posted

Took me a while to get settled back in after San Diego. 

I think some techs may not realize that this is much more than just a hack--  which is its own reward-- but it's a practical demonstration of how understanding the fundamentals of the technology we're working with on modern appliances can empower us as professional technicians to "think outside the flowchart." 

Besides all that, it has an intense cool factor!

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Hacking is fun, and it's easier with the modern stuff. There is a world of possibilities with the technology they're using now vs a simple open/closed switch before all of the cool stuff came out. I've got a chip that will run an inverter for a compressor as well. I like making tools to hack appliances brains.

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Joe B, Stoughton Appliance Repair

Posted

Nice work Walt!

I didn't get a full view of your schematic and couldn't figure out what you did to calculate resistor sizes.  

Can you elaborate?

Thanks!

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Joe B, Stoughton Appliance Repair

Posted

Thanks for the diagram Walt,

I will have to google this, because I'm confused on on what R2 is doing.  It seems to my mind that a properly sized R1 alone would provide a Vdrop so that +out would give a proportional signal to +in.  

It's a good practical exercise, I'll have to investigate.

Thanks again.

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Try it out, see what happens. Sounds like a good project if you can make it work that way. 

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