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Question: Converting HP tx2000 in  to USB Wacom - Need some help
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Author Topic: Converting HP tx2000 in to USB Wacom - Need some help  (Read 17811 times)
Mexicanherder
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« Reply #30 on: April 27, 2011, 12:14:18 AM »

What do you mean extremely smaller?

the resistor on the 5v line is (What i assume to be BROWN), BLACK, BLACK. Which should be 10k, correct?

The other one is also what i assume to be BROWN, GREEN, ORANGE, should be 15k.
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Trashie
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« Reply #31 on: April 27, 2011, 12:54:09 AM »

Uh, i usually cant see resistor colors, just use the multimeter (set to ohm-meter).
R1 is smaller because, if the connection between R1 and R2 is well done:

 Vin=Vr1+Vr2

 Vr1= I * R1
 Vr2= I * R2


 5= Vr1 + 4.45 => Vr1 = 0.55 (and maybe you read 0 in the multimeter).

 As I (intensity) is the same both in R1 and R2, the only way Vr2 is 8 times greater than Vr1, is because R2 is 8 times greater than R1.

All this means : if you've connected well the voltage divider, the voltage drop in R1 cant be 0.It can be 0.55, if you read 4.45 in R2.And, if that happens, is because R1 is 8 times smaller than R2.
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Mexicanherder
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« Reply #32 on: April 27, 2011, 01:09:11 AM »

Ok wow i messed up. I used a 10 Ohm resistor... not 10k Ohm resistor.

Il get a 10k and try again.
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bernard
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« Reply #33 on: April 27, 2011, 04:10:25 AM »

Wow Trashie!  I know who to ask the next time I have questions that only "electronic analog minds" could answer Smiley  (hum, "electric analog mind" just made me have this image of you with a big mesh of semiconductors in your hair).   Grin    Good show.
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Trashie
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« Reply #34 on: May 04, 2011, 07:56:58 AM »

uh, dont expect a lot more than that from me...Really..Basic Ohm and Kirchoff..Still banging my head against transistors :-P

Btw, mexicanherder, if you're still with this thing, i finally made my cable with 2 standard diodes in series with the input..Each one gives a 0.6/0.7 voltage drop, so you finally get 3.8 / 3.6V as input, that looks like it's inside the digitizer tolerance.
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Mexicanherder
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« Reply #35 on: May 07, 2011, 05:49:12 AM »

Yes im still making this thing, havent got around to doing it yet :/
Which diods did you use? i was still having a hard time finding a 10k Sad
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Trashie
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« Reply #36 on: May 07, 2011, 01:43:38 PM »

Check out my build log in http://forum.bongofish.co.uk/index.php?topic=1889.0, you can see how i finished it there.The diodes can be any, you're just interested in the voltage drop.You can find diodes in any old board you have around.
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bernard
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« Reply #37 on: May 08, 2011, 02:04:55 AM »

In case you were wondering, here are some examples of how a diode might look:
http://forum.bongofish.co.uk/index.php?topic=1808.msg13272#msg13272
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