Tuesday, 14 August 2018

Atari ST USB keyboard conversion kit

I have added an Atari ST USB keyboard conversion kit to my Tindie store.
This now has a custom PCB specifically designed for the Atari ST.
When I first built these, I used one of my generic USB keyboard controller boards, with a short cable to connect to the STs keyboard cable.
The cable from the keyboard plugs directly onto the connector on the PCB, and a USB cable into the other end. This should now be a neater solution.
The controller can be mounted at the rear of the case, so the USB cable can be plugged in externally.
Alternatively, it can be mounted on the back of the keyboard (or anywhere else inside the case), if you want a captive USB cable, or plan to install a Raspberry Pi or other small computer inside the case. (see a previous project shoe-horning an intel Nuc inside an Atari ST).
The keyboard incorporates two 9 way D joystick ports, accessible underneath the ST. These are enable and work as USB game controllers, along side the USB keyboard.
This can used used anywhere a normal USB keyboard can be used, with a PC or a Raspberry Pi etc. The keyboard is fully mapped in the controller firmware, so just plug in and you can start typing. Most of the keys map to keys on a modern PC keyboard, those that don't are mapped to something appropriate (Help is set as a Windows key as there isn't one already, and Undo is mapped as Control Z).
The Atari ST USB keyboard conversion kit is available, built and tested, from my Tindie store.

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Tuesday, 31 July 2018

ZX Spectrum IO Interface

I have added a new product to my Tindie store, a simple IO board for the ZX Spectrum,
This gives 16 digital input lines and 16 digital output lines. I've been meaning to build one of these for a while. For quite a while actually. Back in the 1980s in fact. There were some great computer books in those days from a company called Usborne, and they have made several of those titles available online.
I remember these from the time, and read through many of them from cover to cover, over and over again at the time. Very simple books, but they taught me a lot about BASIC. The programs were generally written for the ZX81, with a list of symbols at the side.
At the end of the listing, these would be expanded and would show you lines that needed to be substituted for Commodore, BBC, TRS80 etc. And it was reading those that then allowed me to go and get some of the other books my local library had like '20 games for your TRS80' and convert them to run on my ZX81 (or my 800XL or my Electron etc.)
Where is this going then? Well, there were a couple of books in that range which talked about interfacing with computers, the 'Usborne Electronic Workshop'. One about building Computer Controlled Robots.
And one about Computer Model Controllers. These told you how to interface switches and lights and motors to your computer, and using those to control a train set and things like that. This was great for BBC, VIC20 and Commodore 64 owners, as they had user ports.
But ZX Spectrum owners didn't have user ports, and had to buy 'a special interface circuit', which I don't remember ever seeing. So I made now one. (and yes, that is my own rather battered copy of 'Computer Model Controllers' from the 1980s)
This plugs into the edge connector and gives two 8 bit input ports, and two 8 bit output ports. More than enough to drive your robot or train set.
This is quite a simple unit, the 16 outputs are 74HCT series output, so can sink or source 6mA, enough for LEDs, but needs a transistor or driver chip if you want to control relays or motors. The inputs are TTL level, and will need pull ups or downs as required. There is no protection on any of these pins, so use with care. Each of the four 10 pin headers has 0V, 5V and the 8 input or output lines.
The ports are at 0x01 and 0x03, and can be accessed from BASIC using the OUT and IN commands.
OUT 1, 255
This will turn all of the pins of output port 1 on (5v).
OUT 3, 0
This will turn all the pins of output port 2 off (0v). The output is latched, and will retain this setting until it is changed.
The input command is
IN 1
So for example,
will print the value read from input port 1
Will test to see if digital input pin 4 on port 2 is high
The ZX Spectrum IO board is available from my Tindie store as PCB only, kit or fully assembled.

Yes, this will work on later +2/+3 machines but some adjustment to the port numbers may be necessary to avoid port numbers assigned to the internal hardware on these machines.

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Friday, 27 July 2018

Commodore PET replacement keyboard update

I have updated my Commodore 2001 PET replacement keyboards, they are now available with black PCB soldermask.
The original version was white, which seemed like a good idea, but when fitted, it highlighted how white my 2001 case wasn't.
The black fits in well with the system label and the datasette drive.
Other than the colour, I have moved the connector out of the keyboard area, more like the original, and plated the mounting holes.
This can be seen when the keyboard is mounted in the PET 2001.
Although it will only fit the case of the 2001 PET with integrated datasette. These can be connected to any PET that has a normal / graphics keyboard, one with 20 keys on the keypad on the right. Useful to test if your keyboard just need cleaning, or if there is a fault with the PET.
It is not suitable for PETs (or rather CBMs) with the business keyboard with 11 keys on the keypad (which is usually the 80 column machines).
For PETs with full size keyboards, you can run the cable out of the front. Or use it on the test bench.
These are available from my Tindie store, as PCBs, kits or assembled and tested units, optionally with a pre-wired ribbon cable.

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Tuesday, 24 July 2018

Atari 7800 PAL AV out Composite Video Conversion

Following on from the previous blog post, an AV out composite video conversion of an early NTSC Atari 7800, here we have a later PAL Atari 7800, and I'm going to do the same thing to that.
Although this particular machine is PAL, the board inside looks like it can support PAL or NTSC, with the appropriate jumpers, and suitable Maria, Stella, and ROM chips. (note, there are points marked 'VID' and 'AUD' which do carry these signals presumably as test points, but the video is unbuffered and has the audio subcarrier mixed in, so it's not suitable for direct connection).
There are a few differences in layout to the earlier NTSC only board, but the circuit is basically the same. The main differences are the lack of sockets (other than Maria and the ROM chip), the lack of the side expansion connector (which was never used), and the ROM is 28 pin (and now contains a built in Asteroids game).
Other than those, the rest are PAL versions of the chips in the earlier NTSC machine. This time, the CPU is marked as UM6502, rather than the internal Atari part number, which should be the same as the 6502C, and not the same as the standard 6502 or 65C02.
The TIA chip is very plainly marked, no indication of manufacturer here.
There are some bodge wires on the ROM, also plainly marked.
It is not clear why the bodge wire and resistor are there, but they are there on other 7800 boards as well. There are various jumpers for the ROM chip, including the option to switch the polarity of the chip select from positive (used on the cartridges so it can be wired direct to A12) to negative (as most EPROMs use).
The power input is slightly re-arranged, but still has soft power on capability and that unusual 2 pin power connector.
It seems like they had other ideas in mind when they designed the case.
A 2.1mm DC jack socket fits perfectly in that cutout.
As before, I fitted one, mounted upside down, held in place with a cable tie through the original mounting holes, and wired (centre negative) to the original input pins. This isn't really part of the composite video mod, but I just don't get on with those connectors, so prefer to standardise.
The AV section also has lots of familiar parts.
The parts to be removed are ringed. The same list as usual, different part numbers, but the same circuit.The variable inductor L6 and transistor Q8 are removed to disable the audio subcarrier oscillator. R32, a 6K8 resistor, is removed to separate the audio output from the TIA (but leaving the 1K pullup and 100nF decoupling capacitor in place). R62, a 1K resistor, is removed to separate that section from the point where the video signal is assembled.
The yellow circle shows where the video is picked up from, and the white is the audio. Power is picked up from the supply to the modulator (which is the 5V rail via FB1).
The final thing to remove is the modulator. This version of the PCB is also designed to have a alternative option of a modulator circuit on board, rather than the usual off the shelf canned module. This is protected by masking tape.
With that removed and the board cleaned up, time for the 'Deluxe Composite Video Mod' from The Future Was 8 bit.
This is supplied with a pre-wired detachable cable which just needs to be cut to length depending on application. The video buffer board itself can be mounted to the main PCB using a double sided foam pad or hot melt glue.
The wiring with these new modules is very easy, and picks up on points from the parts that have been removed. Colours should be logical, black for 0V, red for 5V, white for audio, yellow for video.
Just make sure the board is mounted to line up with the hole in the case.
You can then attach the 3.5mm jack to phono plug lead that is supplied with the kit. Here yellow is video, and the red and white jacks both carry the mono audio signal.
Without a cartridge, the 7800 has a built in asteroids game.
This time I do have some 7800 cartridges of the correct region that I can test with. Including this pristine Ms Pac Man cartridge kindly donated by TFW8b #rare.
Which, contrary to it's appearance, works fine.
And of course you can play all your PAL 2600 games.
So that's another system brought up to date with a modern power supply and composite video output.
The 'Deluxe Composite Video Mod' is available from The Future Was 8 bit.

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