Is it alright to say DaveCAD?

Eric Hertz wrote 01/23/2017 at 00:53

I take it ABCD are resistors of different values? Am confused, how's this work? (Don't take that wrong, BJTs are still a bit of black-magic to me).

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davedarko wrote 01/23/2017 at 07:04

They're just pulldowns for the row signal. I only safed one pin, not 4 ;)

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Eric Hertz wrote 01/23/2017 at 10:27

Hahaha, this doesn't help...

Oh, I see... ABCD are connected to GPIOs, as is the transistor-base...

So when the transistor-base (column?) is high, you're scanning the right-side of switches, and when it's low, you're scanning the left-side? So you're saving a column-GPIO. Cool!

Does it work?

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davedarko wrote 01/23/2017 at 11:50

it almost works : ) not sure what's happening with row A atm, it toggles ON OFF on the OFF side. So it works 87.5% of the time... :D

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Eric Hertz wrote 01/23/2017 at 12:06

Probably not related to your 87% problem, but what's the rationale behind tying the emitter to the switches, rather than V+?

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davedarko wrote 01/23/2017 at 12:18

I might have mixed up collector and emitter while drawing, I tend to forget what I see within 2 seconds or so :D you're right, they are.

Edited it, thanks!

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Eric Hertz wrote 01/23/2017 at 14:26

Ah hah! Thought I was 'bouts to learn a new trick ;)

FYI, I think it would've worked, I've recently discovered that transistors can work both ways, "reverse-active mode," where the C and E are swapped. You get the same effect, but much less current-gain.

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davedarko wrote 01/23/2017 at 15:18

Noo, not from me :) but I might have done something like that and wouldn't even have noticed it then? Gotta check... dupdid'oh. Hm, seems like I have in fact mixed up connector and emitter in hardware.

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Eric Hertz wrote 01/24/2017 at 08:30

Haha, maybe better mixing up the E and C than inserting an NPN where you intended a PNP... that can be *really* confusing ;)

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deʃhipu wrote 01/22/2017 at 11:23

But you can't make new part footprints from scratch!

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davedarko wrote 01/22/2017 at 13:11

But I could scratch the footprints..

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