ChibiTerm - Layout status

Projects / ChibiTerm  Original post date: 03/20/2016

tl;dr version: Canada Post finally open their UPS package and it only take them 1 week. Now it is Canada Custom's turn to sit on it. They cleared it! So looks like Custom is treating this as a first class mail. That means that Canada Post might try to deliver this in 2-3 days instead of the usual 7-10 days.

I finally got the 2nd batch of STM32F030F4 that I ordered back and shipped back in Feb 2015. It took 2 months vs last year's 3-4 weeks. I'll try to solder up one from this batch onto the PCB if/when it arrives.

PCB is on order. Hardware files on github
I am expecting some minor mods/layout tweaks for the PCB, so please be patient until the board is tested. Going to take the OSH Park PCB offline for the meanwhile.
Please use the board file for REFDES as they are too small for proper silkscreen.
PCB: 0.7"x1.0" $3.50 for 3 copies from these purple guys. :)

The PCB is the same size as the little green breakout board with all the parts

Canada post tracking

UPS tracking

It takes 5 working days for UPS to just cross the border and put in the mailbox!? Let's hope that this is treated as a first class mail as they are supposed to clear custom and deliver a lot faster than "low priority" packages from China. Things worked a lot faster last December.

Log as follows:

I have been doing a board layout for the past few days. I was on rev 3 of the layout and I thought I finally got everything routed and have a layout that I like. I notice that the board is 0.05" too wide to fit on a protoboard on 0.1" grid. Guess I have to squeeze some more.I'll have to go the other direction to make the board slightly bigger. Rev. 4 is now bigger.

Looks like it won't work without having to put a lot of the component on the back side. Rev 3 layout have optional components on the back side to cut manufacturing cost. In the end, it looks like a bigger board makes more engineering sense.

I managed to make a few layout improvements because of the extra space.

• I managed to get rid of the 0402 cap and relocate the decoupling caps to the front side of the PCB.
• Oscillator - no vias and rotate crystal so that the OSC_In side (high impedance input) is now close to the microcontroller.

Released schematic (click to show original size)

Made some minor changes to the schematic:

• Changed the regulator to MCP1700, but might try out XC6206P332MR (with same pin out) when they arrive from Aliexpress in about a month and a half. :( Those are very cheap 3.3V LDO with support for ceramic caps. They trade off transient response for very low quiescent current.
• Change oscillator to 25MHz crystal for cost saving.
• 3.3V zener diodes on the PS/2 and serial interface. These are located on the back side of the PCB. They are optional, but may save the STM32F030 from accidents. Waiting for shipment from China in about a month and a half.
• The USART registers has option to flip the signal polarity, so might be able to talk to 12V serial port by adding a couple of series resistors (with the zener) at much reduced distances like a few meters.

Going to procrastinate a bit and when I am happy with the PCB, I'll send the file off to OSH Park and post a link for ordering.

Here is what a (single sided) breakout board might look like.

I have done a bit more cleaning up on the board and design.

The buffer video signal has 0.7V drop, so I use a separate series resistor on BACKGROUND signal and for tweaking intensity.
Rerouted a bit for better signal integrity. High speed signals have solid ground under them.

After much procrastination, I have decided to give it a rest and order the darn thing. Order link is up top. The parts on the bottom are optional zener diodes for protection.

3D model of final PCB design - Top

This PCB is the same size as the small green breakout PCB in my prototype. :)