Sunday, July 8, 2012

Project: Wixtel adapter for IRXlate

Wixel Adapter board - middle layer in a three layer sandwich between the IRXlate board on the bottom and Wixel on top.
As I prepared to install the IRXlate, I decided that I really did not want to be taking it apart to install new firmware versions as I improve the firmware, and I needed a solid way to connect to it remotely.
Rather than run cable to it, I figured it was time to break out the Wixel Wireless USB Serial link that I got on sale at Pololu during their 2011 Black Friday sale.

It is easy enough to interface the Wixel to the 3.3v UART connector on the IRXlate, except for the fact that I did not route the power supply to the header, oops.  I'll do that with a engineering change -- a fancy name for a wire under the board.

I needed to build an adapter board to connect the Wixel to the UART header on my IR output board.  I could easily have done that with either my pcb mill, or by etching it, but once you've started working with custom manufactured double sided boards, its a bit hard to go back.  At only $9.90 ($14 with shipping), a 5cm x 5cm PCB from SeeedStudios seemed like the way to go.

I only needed about half that size, so I decided to fill the rest with some other useful circuits and adapters.  SeeedStudios allows PCBs to have multiple designs as long as they are only separated by silkscreen.  I also ordered the 0.6mm width boards so they are easy to cut (as in with a pair of scissors).

I added a MCP1604 based boost convertor design using parts from my most recent Digikey purchase.  This is a flexible design that incorporates a 20mm coin cell battery holder footprint and a four pin header with in and out voltages, ground, and the enable pin.  Changing a few components will get me a convertor that can produce 3.3v, 5v, or many other voltages from a lesser voltage battery, either from the coin cell holder, or wired into the through holes on the board or the header.

I also added a linear regulator based supply that can take either or TO-92 or SOT23 sized regulator.  Again it has a header for the breadboard connection, this time a double row with one row for output voltage and the other for ground.  It is intended to plug into a breadboard power rail.  The input side is connected to two 2.1mm coax power jack footprints, one on each side of the board.  One is connected as center positive, the other as center negative.  I will connect one or the other as needed, or just connect a battery to the appropriate through hole pads.

Basically this gives me ten boost convertors and ten linear regulars that can be built in various configurations for use in a breadboard, or in other designs.  All for free with another board that I have an immediate need for.

The base wixel adapter is all routed completely on the top layer.  Its a five pin header that connects to what is basically a 24 pin .600 spaced dip connector.  On the back of the that board, I reused the 24 pin headers to add some additional SMD footprints that are wired to pins on the DIP connector.  This will give me a bunch of extra SMD to DIP adapters from the nine PCBs that I don't need for the Wixel adapter purpose.

Not a bad payback from my $14.  I ordered the PCBs from Seeed on 6/14 and received the completed boards on 7/1.  That's a 18 day turnaround - not bad at all.

Scans of the board:

Top of Wixel Adapter "Panel"

Bottom of Wixel Adapter "Panel"

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