Retro Repair, Addendum I

In my last post I repaired the mainboard of an old Commodore 64 I had retrieved from the attic. After replacing quite a few components, the board was working again for most practical purposes. One issue remained to be investigated though: under certain circumstances, some characters on the screen would change their color seemingly at random.

Random characters changing their color.

This was already visible in the diagnostics output but turned up again later in a graphics adventure I tried. Besides the VIC chip itself, the static color RAM U6 or the 4066 quad switch logic IC U16 seem likely causes for this problem. Continue reading

First Retro Repair

Commodore 64 “breadbox”.

Recently, I retrieved a Commodore 64 “breadbox” version from my parent’s attic that was given to me by a friend in the early 90s. As I recall, it wasn’t fully functional even back then. It would halt as soon as a program tried to play any sound. But when I connected it now and powered it up, all I got was a black screen.

The broken ASSY NO. 250407.

I took it apart completely, even the keyboard, in order to give the case and all the mechanical parts a good cleaning. Then I went on to see what I could do to fix the “ASSY NO. 250407 REV.B” motherboard that I found inside. Continue reading

Fixing WifiModem64 Version 1.0

As hinted at earlier, I made a couple of mistakes when designing version 1.0 of the WifiModem64 and they will be fixed in version 1.1.

Still, with some minor manual modifications, those first boards are still usable. In short, RTS must be connected to WeMos D7 instead of D8 for the ESP8266 to boot reliably and the WS2812 LED must be connected to WeMos D5 instead of D0 if you intend to use it.

These are the step-by-step instructions to get WifiModem64 V1.0 on line: Continue reading

SyncFix64 Prototype

After the encouraging results of my first attempt to fix the composite signal from a C64, so that the cheap TFT monitor could display it, I shared the idea on Forum64 to double-check and get some feedback. Consensus seems to be that the circuit at least won’t hurt the video source. Since, in addition to that, it seems to be working for me, I decided to design a board for it in KiCAD.

The goal was to make it so small that it would fit inside the display’s case alongside the display controller, so I went for all surface mount components. To get immediate results, I created a single sided layout and etched the board myself using the toner transfer method. Continue reading

Cheap Displays for Old Hardware

A couple of months ago I dug out my old Commodore hardware again and started tinkering with it – the goal being to finally try out a bunch of mods, hacks, and builds that I missed back in the day. To start with, I bought a cheap TFT display for around 13€ to connect to the C64 and C128.

It was meant to sit on my work bench to e.g. quickly test a naked C64 board. It wouldn’t matter if the video quality wasn’t great. But after I made the necessary adapter cable and hooked everything up, I was a little disappointed to find out that the display wouldn’t show anything other than a black screen interrupted by an occasional flicker. I verified that the display itself was working by connecting it to a Raspberry Pi and I double-checked the cable I had made. Continue reading

The Modular WifiModem64

I’ve been playing with the ESP8266 since late 2014 and it was love on first sight: so many possible uses for such a small device at such a low price tag. And very early on I thought: wouldn’t it be great to build a WiFi “modem” from this? That shouldn’t be too hard. But I didn’t find the time to pursue the idea then. When I remembered again this summer, I was not surprised but still excited to find that others had had the same idea and hadn’t been as lazy as me.

Alwyz’s instructions on how to build such a device couldn’t be easier! I followed them and it worked like a charm. For the next months, my setup then looked like variations of this:

Continue reading

SD2IEC Revisited

When I discovered the MMC2IEC / SD2IEC project by chance back in 2009, it made me dig up again my soldering iron and electronic components after many years of disuse. I built myself one of those devices on a prototyping board and had a lot of fun doing so. It was the first time that I got involved with micro controllers and I learned a lot in the process.

Now, many years and projects later, I was looking for an excuse to try out KiCAD and to learn how to design my own boards using it. I had already ordered a small PCB I found on the net as a proof-of-concept to see if the Gerber files I produce would result in working boards. When they turned out just as expected I was eager to create something myself. This was the perfect opportunity to revisit the subject and make myself a brand new SD2IEC.

I wanted the design to be based on Shadowolf’s latest version but also make my own additions and changes:

  • The board should be able to tap into the cassette port of the C64 for power supply.
  • It should be board for external use with proper connectors just like my first build.
  • All components should be cheap to buy from Chinese suppliers.

So, this is the first prototype of what I came up with. I call it the “SD2IEC pluggable”:

Continue reading

Wireless Sensor Network, Part 2

Still trying to save my batteries

By now it is time for at least an intermediate update on this project. In the meantime I have indeed revised the sensor boards by adding a switching transistor controlled through one of the remaining digital pins on the ATmega. The firmware was modified, and it will now power down the attached sensors before entering sleep mode. Disappointingly, this resulted in a battery lifetime extended by no more than roughly 10%.

On a mostly unrelated note, the voltage graph now looks “stepped” when compared to the previous one. This seemed to be a direct result of switching from maniacbug’s original driver for the RF24 module to the one newly optimized by tmrh20. I’ve got absolutely no clue why this would affect the voltage measurement against the bandgap reference, but there it was. If you can shed some light on this, please leave me a comment.

The next thing I tried, somewhat desperately, was to reduce the number of data samples by increasing the sleep time from 1 minute to 5 minutes. This had no discernible effect on battery life-time. But at least it leads to the conclusion that I need to further investigate power consumption during sleep mode.

So, just assuming that it was the sensors that were draining the batteries in sleep mode turned out to be a bad idea. Now I really need to replace my crappy 7€ multimeter with something a little more precise that will allow me to actually measure which part of the circuit is drawing which amount of current.