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Various ramblings – Electronics, radio, old computers, cars & other junk…

Category Archives: Electronics

Progress on the 6502 computer – Milling PCB’s

While work and other commitments have been sapping a large amount of my time I have been making slow progress with the milling of circuit boards for the 6502 computer project. I have added some pictures of progress below.

I am slowly getting the hang of repeatable and reliable results on the mill. Most trouble stems from the height at which the program starts: Cut too deep and the V cutter wears quickly, the tracks wander a bit (following the weave of the fibreglass mesh in the board) and the over all finish is poor. Cut too shallow and you might run into issues with track isolation.

I seem to have found a sweet spot for starting position and depth of cut specified in the GCode, there are methods for using a probe to set height but I have been using some thin thermal docket paper to test height. I carefully jog the Z axis down until the V cutter just cuts the paper without marking the surface of the copper, I hit the “touch off axis” button to set the zero position and then run the program.

I am still tweaking the design of the boards but I am very close to the final revision. Once this is done I can start milling the final version of the boards and begin construction.

First milled PCB

After much tweaking, fiddling and procrastinating I have finally been able to successfully mill a PCB!

The only minor issue I had was with the drill file created by the PCB-GCode script which would not load correctly into LinuxCNC. Luckily this is a step that I can complete manually using my PCB drill.

The results are excellent, the finish is amazing and I am so very happy I won’t have to mess with PCB etchants and toner transfer ever again!

Mistakes on the mill…

While waiting patiently for the mill to finish running a PCB isolation route job I stepped away for a few seconds to skip a song on my music playlist. As I was fiddling with the music I heard the spindle motor starting to bog down and turned around to see that the cutting tool had started cutting deeper and deeper into the PCB material, the MDF board it was resting on and the PVC mill table…

I quickly hit the emergency stop button, killed power to the spindle motor and raised the Z-axis. At first I thought that the program had decided to plunge into the table but it quickly became apparent that was not the case. The heat of the spindle motor had made it slip down in the motor mount, the Z axis stepper had stayed perfectly still the whole time. I tightened the screws that clamp down on the motor and all seems fine now.

No real damage done to the mill, it’s just a little bit annoying… Ahh well!!

PIC Development & Sublime Text 2

While working on a small PIC project as an addition to a larger project (a JUMA RX1 DDS LSB/CW receiver) I had the displeasure of using Microchip’s IDE MPLAB. MPLAB looks like it was designed in the mid-90’s, and while it does let you piece together code and compile it into PIC compatible hex, it’s not the most user friendly program.

While I was battling with MPLAB a friend re-tweeted a link about a new theme for Sublime Text 2, I had a look at the link and the editor looked pretty good! After doing a bit of reading I found out that Sublime Text has the handy ability to call user defined build systems with a hotkey, and as I read on I thought I’d have a crack at getting it working with the XC8 compiler in an attempt to ditch MPLAB.

Linked below is a small project I put together, based very heavily on a set of guides located at Gooligum Electronics. The main requirements to use Sublime to replace MPLAB are a Build System script, and a project specific build file that is launched by the Sublime build system script. This build file specifies various settings (chip type, project name, build options etc…), and is used by the XC8 compiler.

toggle-switch-led-1.0.zip – The most basic of programs, one step above a “Hello World” example. A momentary push-button is used to toggle 2 indicator LED’s along with another output pin that will be connected to the PIC chip in a JUMA RX1 radio (to switch between and display which of the two VFO’s is in use). Alongside the source files are the Sublime project files, one for Mac and one for Windows.

XC8.sublime-build – This is a multi platform version of the XC8 build-system file I am using with Sublime Text. This file will need to be loaded into the correct folder depending on your platform…
Mac: /Library/Application Support/Sublime Text 2/Packages/User/
Windows: C:\Users\<username here>\AppData\Roaming\Sublime Text 2\Packages\User\

Notes:

– The build-system above will need to be tweaked to point at your XC8 install, the project file will need to be pointed at the location of the project. Watch out for back-slashes on Windows, they need to be doubled up (escaped) to be treated as literal in the path.

– You can download the XC8 installer for various platforms here.

– This method can be used to run pretty much anything, you could substitute any build programs/scripts or even flash a microcontroller with this.

Small Wonder Labs SW-40 Kit (Part 3)

With the case finished, there was only one thing left to do… Jam the radio in the case and make it work!

The digital dial kit and main board are secured to the case using brass stand offs (used for securing motherboards in PC cases), once cleaned up they solder rather nicely to the PCB cladding. The lid is secured in the same way. The rest of the boards in the case are secured using double sided tape, they seem fairly well supported and weigh so little that they shouldn’t come free any time soon.

In the photos you can see the main board, the digital dial and a few other additions I made to the radio:

– The most visible is a small LM317 circuit used to step down the 16.5v laptop switchmode PSU. 16.5v is a little high for most of the devices in the case, 14v is just within the maximum spec (and just inside the cut-off volatge for the LM317).

– Located just below the regulator is the RIT tuning module. This is built dead-bug style, with the CMOS logic mounted in a socket which is soldered on to some veroboard up-side-down.

– The final addon board in the pictures is a failed iambic keyer I built, it’s sitting in front of the RIT board. I had a go at troubleshooting it but caved and ordered a picokeyer chip that I plan to build in shortly.

With all that done, the radio just needed a few little finishing touches and it was up and running. I am very happy with the way that it turned out, it performs well and looks great!

The SW-40 kit can be purchased from the Small Wonder Labs.

The digital dial kit can be purchased from Hendricks QRP Kits.