Thursday 10 September 2015

Some laptopification preparations

I have crimped a few minutes among everything that is going on to do a couple of things towards the MEGA65P prototype - the laptop form factor one.

Readers of this blog will know that I already have a suitable panel, batteries and a number of other components for this. What I have been working on lately is seeing how I can lay out the components, and just how big this laptop will end up being.  It turns out quite big, but not exceedingly outrageously so.

The batteries take up about 1/3 of the space, which is quite a lot, although the 3.5" floppy drive doesn't really help much either.  Or the full-sized genuine C65 keyboard with full-travel keys.

I like the safe and robust LiFePO4 batteries, because they are safe and robust. No one wants an exploding C65 on their lap. Also, there is nothing worse than having batteries fail, so that you need to be plugged into the mains all the time.  So I have opted for four quite large LiFePO4 cells. Actually, it is probably fairer to say that I have opted for four VERY large cells. Each is 3.2V / 12Ah, or 38.4Wh each -- as much as the entire battery in some other laptops.  This means that all up the MEGA65P will have 153.6Wh.  That's more than double what my macbook has.

This specification was based in part on the stated current draw of the LCD panel driver that I bought, which claimed up to 3A power consumption.  This would mean that the batteries might only last about 4 hours, although I hoped somewhat more.  I had, however, been ignoring this question until I decided to order a 12V regulator for the prototype.  1A regulators are smaller, cheaper and don't really need a heat sink. However, a 3A regulator at only 80% efficiency might generate more than 7 Watts of heat, and would probably require a heat sink.

So today while we were rearranging some things in the lab, I decided to test the actual power consumption of the LCD panel driver, and also the MEGA65 running on the FPGA board, so that I would know which regulator I need, and also get a good idea of the battery life I could expect.  I was in for a pleasant surprise: The LCD panel never consumes more than 0.61A @ 12V at full brightness, and the FPGA board about 0.59A @ 5V.  This means about 7.5W for the LCD panel and 3W for the FPGA board, or 10.5W all up.  This means that the four LiFePO4 cells should be able to run the MEGA65P prototype for between 14 and 15 hours.  The reality will probably be a bit less, once I add missing peripherals and parts, but it looks like it should comfortably run for 10 hours of continuous use.  This will be a nice result.

I also took a few minutes in the Digital Fabrication Lab here to start modeling laser-cut panels for the MEGA65P.  So far I have just been working on the top panel for the bottom half, trying to get the keyboard cut out right.  This has taken some trial and error, to get all the spaces around the keys even and not excessive, while not being so close as to jam keys (which was actually a problem with my real C65 -- it was a prototype, after all).

You can see here my 3rd iteration, which is almost right. You can see the annotations I have made of what needs to be adjusted.  It already looks kind of cool with the keyboard in. Sorry about the poor image quality -- the camera on my phone is getting rather clapped out. The natural colour of the MDF isn't too far off "commodore beige" ;)  For the actual prototype I will most likely use off-white acrylic or acetel plastic.


  1. Awesome! Regarding the display - would OLEDs be an option, considering the need to make the laptop as energy efficient as possible?

    1. Hello,
      An OLED display would be lovely, but I haven't found one in 1920x1200 with VGA input yet. If this were to be produced in quantity, then we could get more optimal about these things. But for now, it is just about making one unit that works. Also, as I indicated in a recent post I have rather over-specified the battery capacity -- it will have just over 150Wh, so it should be able to run a normal LCD display for somewhere between 10 and 15 hours. If I can make it last an entire international long-haul flight, then I will be happy :)


  2. Personally i'm not so excited about retro laptops as some are, but i can't wait to see the finished c65 repro case - and more news regarding the development and further enhancement of both the softcores and physical stuff :^)

    1. That's okay :) The best way to think about this laptop is me making an easily portable and usable MEGA65 prototype that apart from being rather fun, will make it easier for me to progress development -- instead of being tied to my office seat at home. It will also make it easier to show off the MEGA65 to other interested people.