Thursday, 24 December 2015

Day 24 - Atari ST PC with intel i7

This is day 24 of the Advent Calendar of USB keyboards. Not Ruud Gullit sitting on a shed as predicted, but an Atari ST.
But this is no ordinary Atari ST. It has one of these inside.
Yes, that's an i7 4790K. This is going to take a while, so are you sitting comfortably? Well, it all started with a request for an Atari ST USB keyboard kit, and turned into quite a project. The owner asked if I could install a PC inside the ST, sure not a problem.
He sent me the donor ST and the bits to go inside. The i7 was a little gruntier than I was expecting (atom, Raspberry Pi, the NUC I used on the 800XL PC etc.).There were two main issues to think about here, power and heat.
The Atari ST has an internal power supply, that wouldn't be powerful enough for the new purpose, but it would be good to keep the mains input and power switch, and keep everything internal.
The initial thinking was to use a 12V power brick and something like a Pico PSU which plugs into an ATX connector and just requires a DC input. They only went up to 120W, and the owner was thinking they would need more. (processor TDP=85W, plus RAM, SSD, USB peripherals etc.)
We settled on a miniITX board that had a built in DC-DC and only required a single 19V DC input from a laptop power brick. This is the Asus H81T. All the connectors are along one side and not very high, and it looked like they would line up perfectly with the three D connector slots on the ST case.
There was one problem with that, it left the CPU under the keyboard, so there wouldn't be enough height for a cooler, especially one for an i7.
I did look at a few options, including using an old after market GPU heatsink, bent around to fit on the processor, but it wasn't really going to be viable.
Rotating it around, in both positions where there was sufficient height for the stock intel fan, all those connectors faced inwards. Not ideal, but when it came down to it, not many of those would actually be required. In the end, only the DVI out needed to be extended to the rear panel.
Time to put it all together. I rewired the mains input to feed a 200W laptop power brick, that should be enough power. The motherboard manual was very vague on power requirements, I only knew it was 19V as that was the label on the silkscreen, no actual statement of requirements. In testing, it didn't draw more than 60W, so that should be more than enough overhead.
I left the cable full length, so it could be replaced at a later date with another standard model. The connector on the end was a standard 2.5mm DC jack, so I made up a short lead to connect to the 2 pin header on the motherboard.
Under the power supply plate, I fitted two USB sockets, wired to the internal USB header on the mainboard.
The DVI connection was extended to the rear panel using a short cable, the shortest I could find that would reach. This was DVI-I, so a VGA adapter could still be used if needed.
On the left there, you can see the USB keyboard controller, wired to a single USB header on the mainboard with a short USB lead.
This connects to the Atari ST keyboard with a short cable with mating pins. It's been quite a 3D spacial puzzle fitting all this stuff in, but I like a challenge.
One of the reasons it was easy to go with rotating the board is the audio outputs on the mainboard were not being used. The owner had supplied a USB audio device. This has 4 phono plug for the inputs and outputs, but he wanted two 1/4" jacks, so I made up short leads for those and fitted the sockets on the side of the case.
I kept the original USB lead and plugged it into one of the spare USB ports on the board. Also plugged in there is a USB MIDI adapter.
This originally had 5 pin DIN plugs on to connect directly to an instrument. The ST originally had two 5 pin DIN sockets on the side, so I've rewired the USB MIDI adapter to sockets where the originals were.
The RAM and mSATA SSD are mounted on the mainboard, so no external drives to connect. A DVD-RW drive was requested, but I just couldn't find a space to squeeze it in.
I would normally have added quite a bit of hot melt glue to ensure it all holds in place, but the owner wants to strip it down when they get it and spray it black.
The processor is under the vents on the top of the case, and the side of the case was already cut out to fit a larger floppy drive, so there should be reasonable airflow. The modern i7 processors are a lot more efficient and run far cooler than those of the past. Compare the stock cooler here to the massive Noctua NHD-14 cooler on my old i7 (I've still got that somewhere, anyone want to buy an i7 950 for some old school overclocking?)
Are there it is, an Atari 520STFM running Windows 10, with a little help from an intel i7.
This is the last day of the Advent Calendar of USB keyboards, hope you've made it to the end. Thank you to those that have stuck with me. Time for a bit of a rest now; normal service will resume in the new year.