Osborne 1 Video Adapter.

[cj7hawk]

Hi All,

It's not my schematic - just a repackaging of one of the original Osborne1A's video adapter, but modified to fit in the very tight slot of the Osborne1Bs video/reset/battery bay.

It's a low-profile design and comes out roughly flush with the top of the face, so will pack away nicely. I wil make up a nice case for it so it looks good, and can be easily installed and removed. Due to the design, it only fits properly one way, so should also avoid those incidents of people plugging them in upside down. All of the components sit below are are pretty much touching the O1's surface, so it's very tight in there, and components are either folded flat or fully seated. The potentiometer for the horizontal sync width is seated fully in slots so that the adjustment can be accessed from the PCB side also, keeping it all out of the way.

The main change I made was to switch the sides of the chip swapped the horizontal timer for the vertical timer, mainly to make it all fit nicely.

Happy to share files if anyone is looking to make their own. It's entirely single-sided as you might guess from looking at the copper. ( I love the simplicity of a good single-sided digital design... )

 

[jxm]

Nice and clean!
What PCB mill did you use? I've got a T-Tech that I need to develop a KiCad tool flow for.

 

[cj7hawk]

Just a simple 3060, with a 12000 rpm brushless, and using RNR ECO for the breakout. I run at a lower speed due to the poor quality opto's in the stepper controllers, but the hardware is quite repeatable.

I use FlatCAM 9.4 ( Waiting for Marius to put out 9.5 as an exe ) and autoleveller 0.9.5u2... Also, just figured out with this print I seem to be afflicted with the M31 bug, so set al M31's to -5.

The key to a good result though is the quality of the bits... Most are not really great, and I get mixed results from V tips. But then I found these Chinese bits that are fantastic and I can isolate to 0.0149, so with 50 thou pads, I can fit tracks up to 20 thou across between pads... Which works well.

I use FreePCB since it stores everything local and I don't really like cloud.

But, yeah, the bits are the key that everyone misses. Vtip would be my choice if these weren't available - but it's chalk and cheese between VTIP and these ones.

62 HRC, R0.2x4Dx50L-L2, 1 PCS

https://www.aliexpress.com/item/4000345897484.html

No one else sells anything like them that I've found, save one US company that charges 10 times as much per bit ( and I break a LOT, usually through mistakes... Plus they wear out pretty quickly ) They are a ballnose so put a much nicer angled finish on the edge, and I usually do three passes with 65% overlap, since I usually get a cut width of around 7 to 10 thou not fully going in, and mostly cutting with just the tip.

David.

 

[cj7hawk]

Some pics, before polish, after polish ( just a hard wipe with a bunched up plain tissue to remove burrs etc ) and a close-up with side-lighting to show the grain of the cut, so you can see how clean the ball nose makes the PCB.

It may not look like much, but there's 5 years of experience, pain, trial and error, went into finally getting a good result, while some people get lucky with a mill.drill combo and get it the first time... Also I use the L2 Mill so I can do the entire PCB in one operation - it mills the tracks, then mills the holes, then cuts the PCB out. Which makes it easier to include things like the hole for setting the POT.

 

[jxm]

Wow! It's even more impresive looking at the close up shots.
Thanks for all the info on your tool flow. I'll be checking out FlatCAM and those bits.

Jesse.