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F103 Pod Original post date:02/02/2018
SWD is one of the things I would like to have available without having to open up the case all the time. One way to do that is to fool around with the ID pin and share pins with USB.
I am tempted to use those 10 pin Mini-USB connectors which are used in some cameras for composite video and audio. They are backwards compatible with regular 5-pin USB plugs.
I have ordered 10 receptacle and 10 plugs from
here. I found a datasheet for something that matches the receptacle
here. Unfortunately that means pushing back this project for quite a bit as I want to confirm the footprints before committing to a final PCB design. I guess I could work a bit on the firmware for the time being.
Aliexpress called receptacle a Type-B while the datasheet call it Philips style.
Looks like the receptacle could be a Mini-AB which could accommodate the Mini-B plug which is the only style still used.
The connectors arrived a while back, but I have been procrastinating. The space of the connector pins are such that you don't want to solder it free hand. So I layout a PCB for it, but some of the mechanical dimensions are not easily measurable until you made one. And of course you don't expect to find the mechanical drawings for something on Aliexpress that easily.
So forward to today, I finally made the double sided PCB using toner transfer while doing a batch for a flashlight mod. I used the drill holes for aligning the paper for the second pass of the toner transfer and etching process.
Here is the back side. I have to bend the pins slightly so that it straddles the PCB. (need a thinner PCB). There is a gap between the connector and the PCB to accommodate a plastic bit in the housing. I even file the curvy outline to match the housing.
I stagger the breakout to 0.05" spacing to make it easier to solder. The spacing is such that it would line up with a ribbon cable broken into two rows.
This is how it looks fitting into the the other half of the housing.
Still have no clue how what I need to do on the PCB outline to get boards fabbed. It is small and violates a few of the DRC for copper to outline spacing and a few manufacturing rules. I managed to make on with very primitive hand tools. I guess I'll procrastinate a bit more.
BTW this breakout connector is only need for SWD debugger. A regular Mini-USB can be used for normal operation.
I messed up. I should have made a new footprint for the male side of the connector, but instead I used the female pin ordering. It is a mirror image so the left/right ordering are flipped. I am going to patch this PCB as is. As for the SWD side, I'll fix the layout for the main PCB.
I have spent too much time thinking about round cables vs ribbon cables. I have both types and even the right size, but settled on ribbon cables.
General warning:
Ribbon cables are designed for IDC (Insulation Displacement Connector) and not meant to be soldered. Solder wicks up inside the cable and where flexible part meets non-flexible can create stress points for failures. The staggering helps the front row, but not the back. There isn't much space left, so can't extend the PCB. :(
I separate the wires and work on the short ones first. When that's done, solder down the row of long ones. The cables I have aren't very solderable even with a very aggressive flux and extra flux applied.
There are 2 pairs of 4 conductor ribbon cables. I could have folded a set of 8, but these came from my scrap pile already broken out.
This is how they fit into the housing. The opening is just wide enough. There are two slots on the connector housing meant for a metal strain relief to hold the cable in place. They don't come with one.
I could have cut a tin can or some transformer cores, but settled for 3/8" heat shrink tubing instead. I carefully roll up the heat shrink like a pair of socks with a pair of needle nose pliers. It is not easy, but the tubing is soft so you'll eventually get it. I use low heat (100C) on my hot air tool to shrink the tubing. The fold is slightly wider than the opening, so it would help to retain it. The tubing protect the cable against the sharp corner at the opening and the extra stiffness of the heatshrink helps to spread the flexing point more evenly.
The two halves of the housing snapped together almost seamlessly. I had to pied open this one earlier with a knife which leave some scars.
Once again there are different options for terminating the USB connections. I bought some DIY USB type A plugs, some Micro USB breakout PCB. I settle for the micro USB as they sell cables at the "dollar" store.
I have seen plastic housing for those PCB exactly once and not since. BTW those two holes are for the pegs in the housing, but they sort of work for cable ties and nylon screws too. This is a q&d way of strain relief for the solder joints. Too lazy to add tubing for the exiting cable.
I folded the cable and apply 3/4" heat shrink tubing over the whole thing to prevent shorts from random conductive object in my desk.
Good quality polyolefin tubing get soft sticky and can be weld together by applying pressure while cooling down. All I have is cheap Chinese one here, so I use cheap Chinese super glue to seal the wide opening.
I'll leave the SWD side of the cable unterminated until the pin outs are finalized.
I have seen 4, 5 and 6 pins on the extra I/O, so this is a good thing that the plug physically would not go into other types of mini-USB sockets.
- do not order this version.
