Resistor & diode questions.

[WizardOfWoo]

Hello all.

Gathering materials for a DIY build and I was wondering if the rated wattage on any of the resistors was important? (sorry I didn't see anything specified anywhere, hope I'm not being dumb).

While I'm at it, are there any components in particular you guys would recommend I spend a little extra on to get higher quality? (or perhaps more accurately things I should avoid cheeping out on)

Most my other questions have been answered by searching, so thank you retroactively for everyone who has helped me via time travel .

Kind of blown away by this whole community.

[ignotus]

Any wattage will do. 1/4W seem to be the most common so you can just use those. I suppose tolerance would be more important to make sure everything stays closer to nominal values so I'd use 1% tolerance metal film resistors, though I don't think it's that critical either - won't do any harm either though. Best of luck with your build!

[WizardOfWoo]

That pretty neatly sorts that out, thank you!

Just waiting to arrange ordering a protected chip from Dmitri now I think.

I assume I'm stuck with the 644/1284 chip unless I want to design my own layout and try to surface mount one of those ARM monstrosities? (not happening anytime soon)

EDIT: To avoid spamming new threads I'll just ask here;

I notice that using the 4851 multiplexer instead of the 4051 appears to eliminate the need for any of the 100r resistors and BAT85 diodes right?

If so, is there a more elegant way to then connect up the board other than just wire jumpers where the resistors and diodes would have been?

[ignotus]

Do a search for "all in one PCB" and you can find layouts that use 4851's without all the resistors and diodes. I have a couple but am away from home all week.

[WizardOfWoo]

Do a search for "all in one PCB" and you can find layouts that use 4851's without all the resistors and diodes. I have a couple but am away from home all week.

Thank you. I found Synthex's all in one design though it appears to be double sided (not as confident in my ability to do that + I already have a bunch of 70x100mm copper clads in)

Also lacks the separate mask layers from Dimitri's Kicad which I was hoping to use.

Might just go for wire jumpers if it comes to it.

But it's easy going to be a week or two before I start making anything if you happened to have something suitable for the old two board design stashed away? (I'm guessing probably not with all the crossed channels it would create with one sided boards)

[ignotus]

I'm pretty sure I have a single-sided all-in-one pcb layout somewhere, if you're not in a hurry I can have a look when I get back next week.

[WizardOfWoo]

I'm pretty sure I have a single-sided all-in-one pcb layout somewhere, if you're not in a hurry I can have a look when I get back next week.

That would be wonderful thank you.

Though unless I'm being dense viewtopic.php?f=3&t=96

This one only needs etching on one side right? (assuming I use through hole for everything on the other side which I was planning to do)

Just need to make my own solder mask thingamaboob & get longer copperboard.

If you do have anything better or useful that would still be great though. Time isn't a big factor here. (I'd rather plan thoroughly rather than resolder/etch/replace even if it was)

[ignotus]

That would do, I think I have another PCB by Dmitri with some updated components so I'll send you that too.

[WizardOfWoo]

I think I understand all of that boardmap.

My only questions would be, what is the (I assume) trimpot for? (top, middle right). And what resistance range should it be?

And I notice in the original schematics it specifies a 16MHz x3 and a 12MHz x2. Here it just lists 20MHz and 12MHz.

are the x3 and x2 important?

Or will any 20 & 12MHz crystals do?

Such as this one? https://www.digikey.co.uk/product-detai ... -ND/675584

(sorry for all the questions, this whole project has my brain on fire)

Thank you again for your help.

[ignotus]

The trimpot is for LCD contrast, 10k.

The oscillator values depend on the chip you're using. If you're getting a programmed atmega from Dmitri he'll tell you what crystal to use - probably 20 mhz. Then for the USB-MIDI Pic chip, you can use whatever value you want, I think from 8 to 20 mhz (8, 12, 16 or 20), making sure you flash it with the right firmware.

I'd say any quartz crystal of the right value will do.