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I just purchased an ARPI600 expansion board for my raspberry pi 3b. I wanted this board because it acts as an i/o expansion and allows the rpi to control arduino shields. I have seen this card recommended by many people which is why I was incredibly surprised to see that the documentation for it is ridiculously underwhelming.

It gives information about how to setup the serial debugging function without telling you what it is pretty why you would want it. It tells you how to control the ARPI600 with the pi but does not give you any direction as to what or why. There is little to no documentation on the various pins and jumpers implemented. Most of all I am confused about how to provide power to the ARPI600. I am under the impression it receives a 5v current from another source as the pi can only provide a 3v. But as usual there is no documentation to suggest otherwise or confirm my suspicion. So now I have it all hooked up to the rpi but I am afraid to turn it on for fear of shorting it out or something.

I know that based on the popularity of the product someone has an idea of what their doing but no one with the knowledge has posted anything online. If there is anyone with experience configuring the ARPI600 please let me know. If you just search ARPI600 on Google and you will find the operators manual and see what I mean about the documentation.

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There is an 18 page user manual I presume you are aware of since you mention finding it w/ google. There's also the wiki page (which seems to be a partial copy of the manual).

After glancing through that stuff, I have to strongly disagree that "there is little to no documentation on the various pins and jumpers", although it may be confusing to a neophyte. Which is fine, and it is also fine to ask for clarification about specific things here, preferably by referring to that publicly available information explicitly, and providing a context in terms of something you would like to do or understand. For example:

I am confused about how to provide power to the ARPI600. I am under the impression it receives a 5v current from another source as the pi can only provide a 3v.

The shield has a 40 pin connector, labelled "5. Raspberry Pi connector : for connecting Raspberry Pi" on page 2 of the manual. This should fit directly over the 40 pins of any appropriate model pi. The 26-pin models may or may not work; obviously they may lack some functionality if they do. If you have a 26-pin model, I think it will be safe enough to try since the pins overlap exactly in terms of purpose -- align the connector at the end, where the 5V and 3.3V pins are.

There are probably hundreds of diagrams of the Pi breakout around, so I will not explain that much further here. However, you will notice the first few pins (counting from the corner) include connections to both the 3.3V and the 5V rails (i.e, yes the Pi can power 5V devices). That's where the sheild gets power. Note the logic level of the Pi's GPIO pins is 3.3V, but not all of those 40 pins are GPIOs. "Pin" != "GPIO". Most of them are, but some are power and ground connectors. Again, there are many diagrams and explanations of this around.

It is also possible the sheild could draw power from the USB serial connector, like an Arduino does, although I'm guessing it probably doesn't. In any case, that is for connecting to a PC; PuTTY is an MS Windows based serial console app.

However, the manual is clear that you should have it connected to the Pi and the Pi powered on before you connect any USB serial cable.

Pi 3 Note

There may be a bit of an issue with this device on a Pi 3 since while all the pins are supposed to be the same, the default configuration kind of screws up the UART connection. It will probably be okay, although you may have to take into account the different device node name at some point. It should not cause any harm, in any case.

  • Thank you for your help, I'll be more specific. The 3.3v and 5v rails, are they the only control point for the voltage? Or are they just the ARPI600 side of the voltage control? What I mean is there also setting that has to be edited on the raspberry pi or is just setting the correct jumper all that needs to be done? – Christopher Jul 1 '16 at 4:48
  • Neither. The power pins are not controllable, that's one thing that distinguishes them from GPIO ("general purpose input output) pins. A "rail" is a circuit that delivers a specific voltage and current regulated supply of electricity. That the 5 and 3.3V pins are connected directly to the corresponding rails means that whenever the pi is plugged in (there doesn't even have to be an OS running) those pins are like wall sockets -- they are always live (there are also corresponding 0V ground pins). – goldilocks Jul 1 '16 at 10:56
  • This may be a bit confusing because the GPIOs use 3.3V logic, meaning they can emit and receive digital signals by using or interpreting voltage within a specified range -- e.g., 0V would obviously count as "low", but so does 1V, and 2.5 and 3.3V both count as "high". That's the basis of digital electronics. A signal is a sequence of on (low) and off (high) levels -- hence binary "logic". The GPIOs are for sending and receiving binary logic signals and if you set one as an output on high it will deliver a very modest 3.3V current (~25 mA, as in enough for one LED). – goldilocks Jul 1 '16 at 10:57
  • That's not enough to power the shield; the rails can deliver much more current, perhaps 500+ mA on the 3.3V and 1000+ mA on the 5V (but note the 5V also powers the USB, while the 3.3V powers things like the SoC itself and thus supplies all the GPIOs). So the pins you see marked as 3.3V (usually orange), 5V (red), ground (black) cannot be controlled -- again they are like wall sockets. If the pi is powered (properly) they are powered too. – goldilocks Jul 1 '16 at 10:57
  • So if you insert that shield properly onto the pi (should be easy, but be gentle, especially when wiggling it off) with the pi unplugged, then turn the pi on, the shield is on too. The driver that's mentioned in the docs (cp2102) is I think a Windows driver, i.e., it is needed on the PC if you want to connect that to the shield's USB port. – goldilocks Jul 1 '16 at 10:57

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