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Author Topic: Pickl3bob's tablet conversion  (Read 50825 times)
bernard
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« Reply #135 on: August 21, 2011, 04:34:04 AM »

Hello, hello!

Teensy overheating?  Yeah, possible that. Paul mentioned sometimes talks about heat dissipation, I do not know how to predict this exactly. 

NOTE: You could try to reduce the speed to 8 Mhz but I am not sure it will help that much. Better to find ways to dissipate the heat coming out of the AVR CPU chip.

Once I did an el cheapo heat sink -- I am not 100% sure if it is good or not actually:  I scratched the back of the teensy (where you see an array of dots in a little square -- exactly the size of the AVR CPU) -- this is all "ground". Then I put a *lot* of solder -- making up a little dome.  (I'll try to make a picture when I get the chance).  I need to get myself a decent temperature probe to see if that trick actually makes a difference. But it does not cost much to try it. 

Just got an idea: On there, you could maybe solder a big wire (or lots of small ones twisted together) and run that thick wire elsewhere in the case. (you could leave it with electrical tape or not). This is ground so it is not like high voltage or anything dangerous like that. I did not tried this, but I would believe this might be an OK way to "pipe out" the heat.

Note: the scratching was done with an exacto knife and it was actually quite a pain to do. I should have used my Dremel -- duh!

Of course, the "standard" way of dissipating the heat is to glue or attach a heat sink right on the CPU -- or just attach it with some sort of creative tie wrap construction. (with a bit of thermal paste if you have some).  Heat sink: the bigger the better Smiley
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bernard
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« Reply #136 on: August 22, 2011, 09:40:29 PM »

I forwarded the heating issue to paul to see what he has to say:

Quote from: paul of prjc.com
It should not overheat.  With USB and all peripherals active and running at 16 MHz, Teensy uses approx 30 mA.  At 5 volts, that's only 0.15 watts.  Unless you fully encase Teensy in a nearly perfect thermal insulator, an object the size of Teensy should be able to pretty easily dissipate 150 mW to the ambient air.

Perhaps the failure was due to some other cause than heat?

So I would say: OK to use electrical tape but leave some sort of ventilation "hole".

I asked another question about the heat just in case (i.e. does it make a difference if we draw power from the VCC line [to power the Wacom tablet]. I would think not since I believe the VCC is connected directly to the USB 5V line, not going through the AVR chip).

EDIT: He answered promptly and it is like I suspected: drawing power on the VCC line does not generate heat on the Teensy.

If there is already a lot of surrounding heat around the Teensy (by CCFL or high-powered white LEDs for example) then that could be a problem for the Teensy. It would not be overheating by itself but be overheated by surrounding devices in a closed shell without a chance to vent.
« Last Edit: August 22, 2011, 09:53:47 PM by bernard » Logged
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