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Comment by nathancahill | Hacker News Reader

Pretty neat. Crazy it uses an adhoc wifi network to communicate between the camera and the cartridge. Seems overkill for a battery powered device when they are already plugged in to each other physically.

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Overkill but much easier from a technical point of view considering what was used to make the cartridge.

My first thought would have been to connect the two PIs with a serial interface. Sure, that's another two pins to connect between camera and cartridge, but on the surface it still sounds easier than setting up a reliable ad-hock wifi. The fact that it would use magnitudes less energy is a bonus.

Of course it might be that OP evaluated that and decided against it for good reasons.

But then you need to worry about other things and it's also likely much slower.

Ethernet just works it's an established protocol and there aren't that many easy ways to transfer files other than it today that work out of the box and with any combination of hardware and software.

> you need to worry about other things

Serial I/O is common Hello World example for Raspberry Pi. I think you have to worry about less things than adhoc wifi networks.

> likely much slower

It's slower, but not much slower. The baud rate can be set up to 4,000,000, where a megabyte would transfer in 2 seconds. These "gifs" don't seem to be more than 10 seconds long, so they should be less than 1 MB, judging from random Giphy mp4s.

Is common yes but not as easy you can't easily setup file transfer over serial, in this case a simple FTP to a pre determined folder that the screen grabs the gifs from is a heck of a lot easier to setup than sending a binary file over serial.

Serial?

No, connect them via the USB and configure one of them to appear as a USB Network Interface. Point-to-point connection established. Plenty of HOWTO's available.

Yes, but again this adds complexity. If you use USB you can also emulate one as an MMC device. But overall wifi is simple and guaranteed to work. If this was a product then going the SD card or a "proprietary" protocol is the way to go. But if you are using Ethernet then wifi or wire is simpler. In this case it's also less to worry about electro-mechanical connections.

I needed a wireless connection so the cartridge could slide out completely

It does seem like USB could handle the charging and data transfer with some kind of custom connection to make docking and undocking easy.

"Some kind of custom connection" is the real issue here.

I'm imagining a row of pins along the back or bottom of the cartridge, or an edge connector, like in the old Nintendo cartridges.

Remember how after a few months you'd always have to clean those Nintendo cartridge connections otherwise the game wouldn't load?

My point is that making those types of custom, physical connections are kind of a manufacturing nightmare. If the hobbyist that did this was able to do it with WiFi with no need for more manufacturing and making sure the sled would be able to reliably push the pins in every time, then WiFi was the right call in my eyes!

While it's easy to second guess the decisions that were made here, I have to agree that the solution obviously works fine. Since a physical connection to charge the battery pack was designed in, it seems a shame not to utilize the physical connection for data transfer. I personally have an allergy to using wireless when a physical connection is possible, so that's a bias I bring to the table.

I wonder if there's not an off-the-shelf connector that can be used to route power and USB signals which would fill the role. There's nothing saying the connector has to be small, the entire back and underside of the cartridge is available for the purpose. The original Polaroid film packs had two large pads on the bottom and the camera two long springs to connect with them to provide power from the pack to the camera. However, Polaroid didn't have to contend with ejecting the entire pack with every photo.

My bias says that using wifi adds complexity, but I can see that getting the physical connector right is also not as simple as it first appears.

lol guys go see the album, that is exactly what I have done.. there are two copper pads at the back of the cartridge which make contact with two pogo pins when the cartridge is slid all the way in.. so it can charge when its inside and can also be taken out and removed without a problem

The Raspberru Pi has I2C support, right? I would expect that can be used for data transfer, though it will probably be slow.

Shouldn't be too slow as long as the gif isn't much more than a meg or so.

hey, they arent plugged into each other physically.. the cartridge is completely independent, that's how you can pull it out and take it with you

---strike---They are, see image #9: http://i.imgur.com/Bc4NNAL.mp4 ------

Edit: Oh dear, I see you're the creator. I guess I misunderstood. How do the pins play in to the design if not to connect the two devices?

I don't think you read the description on that. When the cartridge is in the camera, it's getting power from the big battery. When ejected, it switches to internal supply.

Also, you replied to the creator of the camera, so I'm going to guess he knows best :)

yup that's correct, the pogo pins just make contact when it is placed inside the camera so the battery gets charged

haha no problem, those are pogo pins just making touch contact when the cartridge is inside.. once you eject the cartridge its own power source takes over.. slide it back in and it starts charging again

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