[Newbie] - Concept Sanity Check and General Input - Page 1
Forum section: electronics / projects

author: Ohms Public Defender
author_rank: Newbie
timestamp: August 23, 2020, 05:16:17 am
content: Long Time Viewer, First Time Doer,I'm not looking for someone to solve any specific issues (I live for problem solving) but I am looking to see if my concept is sound and if i'm walking down the right path. I have a passive interest in electronics and I'm working on making that more active. The beginner's forum looks like it's geared more towards specific questions/help and I thought this thread fit better here (but if not i'm sorry)I like to come up with stupid ideas, doodle them, and then never actually make them. But one has been nagging at me for a few months. As an IT Gal I've always tinkered with Raspberry Pis as an affordable ARM computer but never found it to be a true usable desktop, with the Pi4 I've reconsidered.Enter the "PiCard" a dumb little doodle for a carrier for a Pi on a PCIe card. The general idea is that this should be able to act as a simple adapter to get the Pi into any PC case, allow it to act as some sort of companion device, and maybe use PCIe as a backplane for "stuff and things" eventually. So this weekend I fired up KiCad, pulled my hair out figuring out how it works, and have become somewhat comfortable with it, enough to want to see if this concept even makes sense to anyone else by making this post.Keep in mind, I have no idea what I'm doingI wanted to make the card flexible. In theory a Pi could be mounted USB side to the right and, though a kludgy mess of cables, provide I/O at the back of a computer case (left). This would be 2x USB 2.0, 2x HDMI (Right-Angled to fit), 1x USB 3.0, and Ethernet. Alternatively, with Rear I/O unpopulated the Pi can be rotated to simply stick out of the case or flipped entirely to allow for some sort of large cooling device (though the primary mode would be as first described).Elsewhere on the board are some basic "Quality of Life" features that make using the Pi in this manner more tolerable. A Power LED and Switch and various GPIO headers the most obvious.To achieve this I'm envisioning using small patch cables to easily adapt interfaces. This would include a USB 2 header to feed a Hub that powers the rear and internal USB 2.0. USB C for SATA storage (and rear I/O, though I haven't quite reconciled that just yet) and some form of HDMI patch that isn't shown above. I know the USB hub can be done through I2C but I wanted to leave GPIO as open as possible and minimize changes in software (general philosophy is that it should be as easy as plugging the Pi in to the board and turning it on) though how much value this really has i'm not sure.The primary advantage to using PCIe is being able to scavenge power directly from the host computer if present this is where the mess at the bottom of the board comes into play (and what i'm most ashamed of at present). I believe (but haven't completely confirmed) that the hotplug pins on the PCIe connector must connect for the card to receive power, and to keep the card flexible I made that a jumper, and then I just made all of the rails jumpers, and then I was a little worried about the size of the traces so I made the massive, and well, that's why there's a big ground plane with random Vias in it.It's a work in progress.Regardless, this will eventually be used to power the Pi using USB and provide misc. power points on the card where they fit.You'll also notice I've made sure to make the card look cool now before the layout is finished (because honestly this helped me work with KiCad and vent frustration when I couldn't get it to do what I wanted)You've probably also noticed a distinct lack of traces.So, flipping the board around you'll also notice lots of missing traces. I haven't quite worked out differential pairs just yet, but I wanted to try and get the major components before I tackled that.In the center of the board i'm hoping to put an M.2 slot for a SATA SSD to be mounted directly on board, but i'd also like to leave provisions for a standard plug with "some switch thing" (as i've called it in the pcb layout) to allow this to be user configurable.I'm sure the ICs aren't the most optimal solution but i'm not married to anything (I just went on Digikey and Mouser until I found the part that looked the easiest to solder by hand that did what I wanted it to do)From there I know I want to add in TTL Serial to make the whole thing more usable from the host computer.I've attached what I think is the correct KiCad file if you'd like to take a look.Really what i'm asking is if the concept is sound and if i've made any major design errors or assumptions that will come and bite me in the ass later.Thanks