MEGAphone: Integrating it all into a working package

Okay, so recent posts have covered the initial rugged case design and the telephony software side of things.  Then behind those, we have the various hardware modules needed to make the whole thing work.  So let's start pulling this all together and make a working battery-powered portable MEGAphone that wakes up from deep sleep when you ring it.

Requirements (Milestone 3.a)

So here are our requirements that we will need to address:

1. Connect battery to appropriate DC:DC converters to power the thing.

2. Connect power management FPGA to the DC:DC converter enable line so that it can power it on and off when required. 

3. Connect power button to power management FPGA to allow on-demand wake-up. 

4. Connect a RESET button to the MEGA65 so that it can be reset without powering off when required.

5. Connect header to the MEGA65 main board to make it easier to connect the 2nd UART to the MEGA65's keyboard connector, instead of needing a fiddly extra cable.

6. Fix the power management FPGA and MEGA65 mainboards onto the appropriate "decks" of the stack of boards that make the inside of the rugged case.

7. Figure out the wiring routing for all the connections between the boards, and make that much easier to follow and to wire up.

8. Document anything else that's needed to put it all together.

9. Verify that it works.

Okay, so let's start at the beginning, then.

1. Battery to DC:DC Converter

For this, we are using a DC:DC converter eval board while I wait for our custom high-current DC:DC module to be ready, and also because we need 12V for the 15" LCD panel and also for the MEGA65.

8. Document everything else needed to put it all together, and confirm that it works (Milestones 3.b, 3.c, and 3.e)

For this I've added a table of the fixing parts into the keyboard cut-out area, and then started putting markings to indicate which screws and things to use.  I also took the liberty to add a fun cold-war inspired block of text and the MEGA65 logo to the spare space above the keyboard, and add in a fake "authorisation codes biscuit" in the waste cut-out area with some handy short-cuts:

 

I'll work my way through the other decks doing the same kind of thing, showing the fixings I'm using on each level, to make assembly easier for others.

As I'm going through and putting the battery system together, I'm really wanting to have a complete battery isolation switch, probably accessible from the outside of the case -- at least while I'm prototyping like this, and don't yet have an integrated battery charger in the thing.

There are plenty of good battery isolation switches, e.g., https://www.jaycar.com.au/high-quality-120a-battery-isolation-switch/p/SF2245, but they are quite chunky, so I'll have to see if I can make the clearance for it.  I feels like it should be totally possible, though.

 

The only problem is that the threads for this are too large for the 8mm ring connectors, so I'll have to get some bigger ones. So another trip back to Jaycar tomorrow.

 Actually, I reckon I can put it through the various layers and anchor it in the second-bottom deck, and have it protrude up into the "floppy disk storage bay" -- and when the big red key is removed, still have space for some floppies.  I can even add "ISOLATE" and "ENGAGE" or "AUTHORISE" or similar to add even more to the cold-war era vibe of the machine... but I'll have to choose my words carefully so that I don't have problems carrying it through airport security or similar!

So let's work out what we need in terms of holes.  The stem is ~22mm in diameter. We'll go for 23mm.  Then the mounting holes are 6mm in diameter and 39mm apart.  Then we need an 18mm wide and 53mm long, rotated 90 degrees from those two mounting holes.  

The depth of the back of the switch means that it will need to be cut into the 3rd deck, while the stem and mounting holes would need to be cut in the 2nd deck. That would result in the stem poking all the way up through the "floppy disk bay", meaning no floppies could be stored there or inserted into the drive.  So it would be better to put it one deck further down, and will thus require a cut-out in the bottom deck. Fortunately we have an unused area down there.

Here's how the layer looks with the the labeling: 

 

I've also added a cable path for the phone curly cord, so that it can sit in there more easily.  The last change I need to make to the laser cut files now is to add holes for the joystick ports to allow the use of DB9 extension cables to expose those.  Using off the shelf cables is much easier, but does increase the depth of the cables through the stack. But I've figured out I can hide them underneath the phone handset.  If I make the right size cut-outs in the next layer down, they should basically be wedged into place, without requiring any screws, which is good, because the thumb-screws on the cables I can find aren't really designed for 3mm thick material.  I'll also have to have slots in those cut-outs on the lower level that reach to an edge or to a larger void that can pass the whole cable head through, so that it can actually be assembled.

My biggest problem here is that the cables are 1.8m long, so will add quite some internal bulk and requires some creative circuitous routing in free space, but it should work.  

In fact, I ended up dealing with all sorts of problems getting the wiring loom to work, and getting the core telephony stuff in there and working. The main part of that adventure covering getting appropriate work-around modules, figuring out the wiring, testing each part, and remediating the various problems encountered along the way -- culminating in it being able to run the telephony software is documented in this fairly epically long post.

That just leaves us with the final demonstration of integration here: Watching it turn itself on in response to a phone call, and correctly launching the phone software when that happens. So without further delay:

There really isn't that much more to show -- it's the output of a lot of behind the scenes work pulling this all together. From here, it's about refining a system that has working fundamentals. Smaller. Faster. Lighter.