un1b0x - 2020 EUzebox BOM

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danboid
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Re: un1b0x - 2020 EUzebox BOM

Post by danboid » Thu Jul 30, 2020 8:29 pm

The instructions for flashing the bootlloader have a lot of room for improvement.

They're not included in the BL github README (which gives a link to a forum post), they're Windows only and they're also incomplete. I was able to work out how to set the fuses but I'm not sure how you flash the bootloader hex. This should be covered in the README along with instructions on how to do it with avrdude under at least Linux.

The README takes you here:

viewtopic.php?p=3847#p3847

It tells you to set the fuses first and shows you the Atmel/AVR Studio device programmer window but it doesn't explain thats what it is or how where to find it under Studio, that would be helpful to Studio newbs like me.

The very vague instructions for flashing the boot loader amount to:
Then flash the following HEX:
I presume this is done by going to Memory (under the device programmer window) then Flash is it?

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Artcfox
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Re: un1b0x - 2020 EUzebox BOM

Post by Artcfox » Fri Jul 31, 2020 2:12 pm

Use uzebox/demos/Bootloader5, see thread here:

viewtopic.php?f=3&t=9405

and see the last page for detailed instructions, which may have been added to its readme.

It looks like you are using the super old bootloader, which doesn't support SDHC. Jubatian rewrote the new Bootloader5 from scratch, definitely use that one.

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danboid
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Re: un1b0x - 2020 EUzebox BOM

Post by danboid » Sun Aug 02, 2020 4:33 pm

No, I've been flashing the latest Bootloader5 as built from git.

As for the instructions, I'm referring to how to use Atmel Studio to flash the bootloader, not avrdude. I think the way I tried is the only way you can do it under Atmel Studio, but it'd be nice to have some verification.

I suspect I'm going to have to start over with my build, once I've got some larger breadboards. I don't think the one I used for this first attempt is quite big enough.

The reason I think I'll have to start over is down to how I wired up the crystal, it probably isn't valid. I tried to describe this in a previous post but I didn't provide an image so it probably wasn't very clear what I did so I'm trying to rectify that now.

The Euzebox schematic shows the following highlighted connections when wiring up the crystal:
Screenshot from 2020-07-30 19-47-21.png
Screenshot from 2020-07-30 19-47-21.png (63.71 KiB) Viewed 1616 times
I presumed that those highlighted connections were only required if you are using MIDI which I presume requires a second crystal, hence if you're not adding MIDI you could ignore these connection points and instead connect one leg of the crystal to one leg of the 22pf cap and connect that point to one of the XTAL inputs on the MCU. I did that for both of the crystal connections.

Here is a drawing to show how I connected the 22pf caps and the crystal to the MCU. The yellow lines represent wires added later:
mpv-shot0001.jpg
mpv-shot0001.jpg (200.76 KiB) Viewed 1616 times
Could that work or is it a definite no-no?

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Artcfox
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Re: un1b0x - 2020 EUzebox BOM

Post by Artcfox » Sun Aug 02, 2020 5:10 pm

I'm not sure if that would work or not, I've just always been told that the crystal pins should be placed as close as possible to the pins they are connected to on the uC.

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danboid
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Re: un1b0x - 2020 EUzebox BOM

Post by danboid » Mon Aug 03, 2020 10:45 am

Hopefully Jubatian or CunningFellow will be able to tell me if I have to start over with this.

I'd be interested to see how others who have made breadboard UBs have wired the crystal up. There are a few broadboard UBs shown on http://uzebox.org/wiki/Homemade_Uzeboxe ... d_projects but it only shows pics of the top sides of the boards.

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Artcfox
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Re: un1b0x - 2020 EUzebox BOM

Post by Artcfox » Mon Aug 03, 2020 1:13 pm

Desolder the crystal and put it right next to the pins they connect to? Then make the caps touch those crystal pins and GND?

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Jubatian
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Re: un1b0x - 2020 EUzebox BOM

Post by Jubatian » Tue Aug 04, 2020 6:21 pm

Sorry, didn't visit the board for a few days! Yes, the crystal definitely has to go right next to those pins! The problem is that it is extremely sensitive, the capacitance of those wires may be too much! 22pF is very little! So yes, desolder, and put it right next to those pins! (Like how it is even on my hackish boards here, notice where the crytal and its caps are on both). Also pay attention to the placement of the 100nF cap, it should go next to the power input of the AVR, on either side, there again the electrical characteristics of long wires would defeat their purpose. It is important to pay attention to these especially so on the Uzebox since it is overclocked, so even driving the crystal it might not quite do as well like an AVR used within its specified operational limits.

Looking at the board, yes! At this point, assuming you connected the Scart right, you see the Uzebox with the programmer, you set the fuses to start with Bootloader and use the external clock, then the Bootloader should start and you should get a picture! I think you should try until sorting that out, if you can program the AVR, check the fuses, make sure they are right, then if and as necessary, make sure electrical connections are there, everything for the Scart is wired up, including grounds to those pins which should be grounds.

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danboid
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Re: un1b0x - 2020 EUzebox BOM

Post by danboid » Wed Aug 05, 2020 9:55 pm

Thanks Jubatian!

I would prefer to get this build fixed up and running first or else I have wasted 2+ weeks but I think there is a good chance I will have to start over.

I think I can see the crystal in your photos and it looks like it is only separated from the AVR by only one row of holes so I presume you probably bent the legs of the crystal onto the pins of the relevant pins of the MCU without using any extra wires and without using any extra 'connections' as shown in the Euzebox schematic section I highlighted in my previous post. This also kinda contradicts the Euzebox layout drawing where the 22pf caps have been placed inbetween the crystal and the MCU:

Screenshot from 2020-08-05 21-34-01.png
Screenshot from 2020-08-05 21-34-01.png (25.87 KiB) Viewed 1525 times
I could de-solder and attempt to reuse the same crystal but I find desoldering a pain. I'll prob desolder the current crystal but I want to replace it with a new one as I don't fancy my chances of reusing the existing one and actually having it work, besides I cut its legs off last time. Thankfully, it seems Farnell sell the correct crystal so I don't have to pay the crazy Digi-key postage nor pay literally 10x the price to buy some on Amazon:

https://uk.farnell.com/txc/9b-28-63636m ... %20crystal

Has anyone got any tips on connecting more than two solid wires? There have been a few times in putting together the UB where I've had to solder together more than 2 wires so I've basically tried to overlap the contacts as best I can and cover them in solder but it just feels a bit awkward and likely to cause problems. Is there anything I can do to ensure a good connection in such cases? The wires seem a bit too short to twist them together.

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Artcfox
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Re: un1b0x - 2020 EUzebox BOM

Post by Artcfox » Thu Aug 06, 2020 4:08 am

Put all three wires through adjacent holes in the perfboard, and bend them onto each other and solder them? Personally, I love using these for permanent prototypes as they are connected in the back just like a real breadboard: https://www.adafruit.com/product/1606

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Jubatian
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Re: un1b0x - 2020 EUzebox BOM

Post by Jubatian » Thu Aug 06, 2020 6:09 pm

danboid wrote:
Wed Aug 05, 2020 9:55 pm
This also kinda contradicts the Euzebox layout drawing where the 22pf caps have been placed inbetween the crystal and the MCU
That one doesn't matter! :) The point is keeping the wires short, where you hook up the caps to it doesn't really make a change. On mine they are behind the crystal since that fit easier (as the other lead of both needs to go to ground, so I could just shove them together in the same perfboard hole to solder them to the ground net, not to mention that the long cap leads serve well for providing a good length of ground wire). And yes, on those boards the crytal's leads are used to make the connection with the MCU pins.
danboid wrote:
Wed Aug 05, 2020 9:55 pm
Has anyone got any tips on connecting more than two solid wires?
I typically do it by making a small hook on the end of the wires which I add to connect things. When using component leads, the very nice thing is that they are rigid, so you can pre-bend them into the correct shape, and once you soldered one point, it stays. So those difficult holes where multiple wires meet become much easier due to this, as the wires won't go living their own independent lives as soon as the solder loosens, they would just stay there. For getting them positioned, I put small hooks on the ends of a section so they get caught in the hole they are intended to be soldered to. Unless of course something is already there, then it is a bit trickier, but the point is that if it can be soldered firmly to the board somewhere, it is rigid, so stays.

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