HW: column transistors are backwards.

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On the schematic the column transistors are the reverse from Peggy2.  

I was trying to figure out why the row drivers were not performing very well.  
They seemed current starved when the resistor value was to low.  I tried 
reversing the column transistor on a whim and was able to get brighter LEDs 
without red winning as much.

I measured the current for both as marked on ClockTWO schematic and reversed 
and got 3X more current with transistor reversed!  

Then I tried to understand transistors (to no avail).  

Finally I looked at the Peggy2 schematic, voila.  Our transistors are 
backwards.  

Original issue reported on code.google.com by wyojus...@gmail.com on 6 Dec 2010 at 11:35

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See http://evilmadscience.com/KitInstrux/peggy2.pdf

Original comment by wyojus...@gmail.com on 7 Dec 2010 at 2:10

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Also, from 2N5401 data sheet it shows that they can only source 600 mA.  Thus 
the current starvation.  Our LEDs can draw 90 mA each * 10 = 900 mA.  That is 
without over driving them.  Maybe we should search out another transistor.

Original comment by wyojus...@gmail.com on 7 Dec 2010 at 2:13

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Transistor polarity seems OK on the schematic, but is reversed on the PCB 
layout. Here's what we can do :
1. Use the existing transistors we already ordered for ClockTWO boards.
2. Order out new transistors just for the ClockTWO boards. These seem a good 
fit : 
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ZTX953-ND 
(Digi-Key Part Number ZTX953-ND )
3. For ClockTHREE, use these : 
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=KSH32CTFCT-ND 
(Digi-Key Part Number KSH32CTFCT-ND )

I tried a TIP32C PNP (Digi-Key Part Number TIP32CTU-ND) on the first column, 
and it seems to improve considerably. But, these are too big for ClockTWO board 
(TO-220 package)

Original comment by anoo...@gmail.com on 7 Dec 2010 at 6:30

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Original comment by wyojus...@gmail.com on 11 Dec 2010 at 1:38

• Changed title: HW: column transistors are backwards.

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Closed on TJS final review

Original comment by wyojus...@gmail.com on 5 Jan 2011 at 12:41

• Changed state: Fixed