If I want to power a second device from the OpenMV, can I only power 3.3V devices, say from the 3.3V rail below P6? Can I not pass the USB connection’s 5V on to another device?
Yeah, we don’t pass the USB 5V. That’s also something we won’t ever do. It would be kinda like a USB violation.
Hmmm, are you saying that there is some sort of “violation” involved in the fact that an Adafruit FT232H has a 5V supply line?
Hmm, okay, I guess it makes sense for that. I suppose the Arduino outputs 5v too from USB.
Anyway, if you need 5v you can solder a wire to the connector pin on the USB connector. It’s exposed.
As for adding a 5V output pin on the camera. I guess if we moved BOOT0 there would be space.
As I’ve said before, I’m not specifically urging any design changes, much less extra work, unless the broader community sees utility in such requests.
Yeah I thought more about this and what we can do for any future version is to expose some holes for 5V and GND that you can manually wire up. They wouldn’t be on the two side connectors however.
That would be a great half-way solution. Anyone can stick a wire through a via, but solder-hacking the teeny USB connections is a different level of involvement for some folks.
The ship has already sailed for the H7 however. But, hopefully sales will be great on it and we’ll be doing a lot of manufacturing runs where we can iterate.
I was talking to my electronics buddy about the proposal of tapping into the USB 5V line and he asked why I couldn’t just get 5V off of VIN while the USB power is plugged in. I told him it was my understanding that the VIN pin only operates as an alternate incoming power source to the M7, but not that it reversibly provides power output when the source is USB.
What is correct here?
There’s a diode near the USB connector that has 5v on it that’s much easier to connect to. Check the schematic and board design in Eagle to see where to tap into.
If you look at the electrical schematic you’ll see that we use an Or’ing didoe to OR the VIN and 5v together. They can’t interact however because the diode is there. If you under solder the diode and bridge it’s connections you’ll get 5V out on the VIN. It’s very dangerous however since you can also inject VIN into the USB cable however.
The didoe is that 5 pin black transistor like looking IC.
Ah, thanks! After you pointed me to the diode, I quickly found the correct contact with the multimeter. It’s even one of the contacts toward the edge of the board instead of toward the middle (anode #2 according to the diode’s datasheet). That will be a pretty easy connection to make.
Sorry for all the trouble on this, but it would be great to power my entire setup from a single cable and of course I want that cable to be going into the M7 as opposed to elsewhere in the arrangement so that I can use the IDE.
Yeah, just put a solder blob over the diode to bypass it.
So I started by identifying the correct contact point. This photo indicates the 5V line of the USB (which would make for a much more challenging mod, as the attachment is minuscule and tucked into the board’s circuitry) and the 5V anode of the diode (which is somewhat larger and considerably more isolated from nearby metal, thereby significantly easing the intended soldering job, as recommended by kwagyeman).
I soldered a two-pin female attachment to the diode, with one pin above the board connected to 5V and another under the board that I then connected to the ground pin. This second ground connection wasn’t necessary since there is already ground access on the board, but I thought it might be nice to support a two-pin power/ground pair, plus I liked how the two leads of the female pins wrapped over and under the board snuggly.
But, since I used Gorilla glue to stabilize the attachment (instead of fabric/glue-gun glue as would be more traditional), the glue expanded through the back of the header (gorilla glue expands quite a bit as it dries), completely filling the female leads with glue. By the time I had drilled them out with a 1/16" bit (which is too big, despite being the smallest standard drill bit), I had destroyed the female header. So I clipped all the plastic away, exposing the leads inside the female header, still soldered to the 5V anode and the ground pin via the copper wire (see above), but otherwise hanging off the edge of the board, and finally soldered a two-pin male header to the remainder of the female attachment hanging off the edge of the board. I chose male over female for the second attempt to avoid repeating the exact same error all over again. Blech. What a hack-job, but it’s done now. I should really stick to software.
So now I can power a second 5V device (a SPI device that the OpenMV interacts with) without providing that device with a superfluous power cable.
Great write up! On the H7 we made this harder however with a new circuit that is an ideal diode to minimize voltage drop so as to allow for batteries to work longer with the H7.
When we do another H7 production run we can include some solder pads for 5V. I don’t think there’s space for holes but we can probably make a large copper area.
If you have any thoughts at all on how to access the 5V on the H7, please let me know. I have access to a professional circuit-builder. He’s…kinda incredible, so he can handle any soldering task I throw at him if there is even a merely schematic way to accomplish the hack. Of course, I suppose I could quite easily build a custom cable that splices and forks out the 5V line just behind the end-plug…but yuck!
Buying a different type of 5V USB cable like a Y cable is probably easier.
Out of curiosity, are you saying the diode in the same location on the H7 doesn’t have an anode directly connected to 5V? I admit the H7 is a little more crowded so the diode isn’t as easily exposed as I took advantage of (it looks like there is a resister just below it), but are you saying it is not actually connected the same way such that 5V isn’t even an option despite the similar-looking layout in the photos?
Um, it’s a different circuit. We’ll release the schematics soon for it.