Help with homemade arduboy schematic

No, it should remain as you have it now. UVCC should be F1 output, U4 VCC/CE, U2 UVcc/VBus.

I have a similar one. You can get 10 pin to 6 pin adapters.

Note that I found that the programmer I have wasn’t fully 3.3V compatible. Yours is different than mine, so I don’t know if it has the same problem.

No you haven’t. GND should be on pins 4, 6, 8, 10 not 1, 3, 5, 7

I moved the index pin too, the black tab on the top of the connector, isn’t it right?

The position of the index tab is correct with relation to the signal names. The pin numbers are wrong. Look at the silk screen of the programmer in the photo you linked to. Pin 1 is MOSI and Pin 9 is MISO.

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Ok I fixed that, thanks. The design manager kept giving me a warning about multiple nets in the same wire, so I merged the nets B+, VBAT_CHARGE and P+ into B+. And I’ve deleted P- because it just connected to ground. Have I messed something up?

I don’t see any more problems (but again, I haven’t checked that all the ATmega I/O pins are wired to the correct parts).

Many of the names (xxx_PAD) you’ve given to your test pins don’t match what they’re connected to (and you don’t have a T7).


I’ve followed the pin table (Arduboy
Leonardo/Micro column) you linked me in your first reply and MrBlinky’s thread about the flash cart so everything should be ok

Damn all these dumb mistakes… fixed them
Now I can finally get my hands dirty and lay out the pcb :smile:

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You might be better to name the PF0 and PF1 test pins after their Arduino pin names.
PF0 = A5
PF1 = A4

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You have the flash memory chip wired according to the “old” design, where CS is wired to PD2 (RX). You should probably follow the “new” design, where CS is wired to PD1 (SDA).

But in the post there’s a note saying “Use new wiring only when hardware serial will be used for special tasks” and personally I think I will never use the Serial Communication, maybe it’s more likely that I’ll use the SDA and SCL for I2C communication, I’ve also got some sensors that use I2C.
I was thinking about using a resettable fuse instead of the normal one, can the leakage current damage the circuit? What do you suggest me?

OK, but the upcoming official FX mod will use the “new” wiring, so it will likely take less effort to use it. Then again, maybe the “old” wiring is easy, as well. Maybe @Mr.Blinky can weigh in on this?

You could probably still use I2C with the “new” wiring, as long as you didn’t write to or read from the flash chip or display while using the I2C bus.

I assumed you were going to use a resettable polyfuse.

What leakage current?

Leakage current of the resettable fuse

There’s nowhere for current to “leak” from a resettable fuse. A polyfuse may have a bit more resistance when operating than a normal one, but that shouldn’t be a problem.

Here it says that PTC fuses have some leakage current during the “tripped” status. Maybe I’m just confused and and a PTC and a resettable fuse/polyfuse are two different things?

The fuse is to protect from burning up traces or damaging components on you circuit board, due to high current or a short caused by a wire or some other device. If the high current is due to something other than a dead short, that component is likely already damaged. The small amount of leakage current that can flow though a tripped polyfuse will be so low that it won’t be able to cause any further damage.

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Oh ok, thanks for the explanation

Fuse leakage could be a problem if high voltages were involved, where a person could get an electrical shock, due to leakage causing the circuit to still be live. The person might assume that the circuit is safe to touch because the fuse has tripped.

Your voltages will be 5V or less, so the danger of electrocution isn’t an issue.

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When choosing a PTC, should I look at the Holding current or the Trip current value? I’ve read that if the current passing through the PTC is between the Holding current and the Trip current, the fuse might trip anyway depening on external factors including how much time a current has been passing through it. Considering that the battery should take about 2 hours to fully charge, is it better to choose a PTC with a Holding current or a Trip current of 1.1A?

You have to make sure the hold current is higher than the maximum average sustained current that the circuit will draw. “Sustained” time is on the order of minutes, not hours. Therefore, if you’re going to be charging at 1A then you need a hold current above that, so a 1.1A or a bit higher hold current is what you’re looking for. However, you want the trip current to be as low as possible above the hold current, so as to offer the best overcurrent protection.

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I should probably change that. There’s a little history behind it but I won’t go into to much detail.

Rx was the prefered method. Then there where ideas to use serial for multiplayer and SDA was added as an alternative. Even with using SDA, I2C should still be usable as long as there are no SPI transfers during I2C communications.

SDA was chosen as flash chip select for the official FX mod chip for easier assembly and soldering.

You are Free to choose Rx or SDA for flash chip select. It comes down on whats important for you. If recompiling games isn’t an issue for you then you can use Rx and have the possibility to use I2C without limitations.

If you don’t want to recompile games and play original unmodified games. Then you’d better choose to use SDA as once the FX is out FX enabled games will come out.


I think I’ll follow the new wiring then, thank you for the explanation