Tuesday, January 22, 2019

What do you mean I can't title this post "Whats that Pong?"...

..as RetroManCave already used it?

By sheer coincidence, one of my favourite YouTubers did a video on a Pong clone that used an AY-3-8500 chip as it's core. I too, have one of these which I got before Christmas from my Dad. Mine, however, is a little bit different.

Presenting the Interstate 1125 console from 1978 with around 30 years worth of dust! This was THE first games console that our family had and I remember sitting in front of the our ancient CRT TV (with fake wood case and manual tuning knobs) with the mini analogue joysticks and a single, tiny red fire button trying to hit more crosses or score more goals than my twin brother. 

Anybody? No? Dust? Anybody? No? Dust?

Memories aside, there are several interesting points about this console. It has cartridges which is unusual for this brand. The suggestion is that more cartridges would have appeared to slake our thirst for more, and bigger games. Sadly, while others may have been available, we only had the 610 cartridge. I was quite surprised to see while preparing this post that there were at least four other cartridges available, the 601, 603, 604 and 605. 

First things first, I need to find a power supply. Fortunately, my multipurpose supply that I use for my oscilloscope has the right voltage and has the right adaptor - which is rather bizarrely a 3.5mm single pole jack i.e. a mono headphone plug.

Next, this thing will only output RF and, somehow, I need to modify it to do composite as my LCD panel will only take composite or HDMI. Having done this before on the Spectrum I had a hunch that it would be very similar i.e. disconnect the RF modulator and re-connect the input straight to the centre pin of the video out. 

Let's get that top off. First problem was the cartridge which, having been in-situ for NEARLY 40 YEARS didn't want to come out. A few minutes of gently pushing, pulling and wiggling finally released it. I wondered what was inside....(side quest incoming)...

Ohh, look at that!
Inside is an AY-3-8610 chip, manufactured week 44 of 1978 (for reference I was four years old at the time). This is an interesting beast as it is a dedicated 'pong on a chip' developed by General Instruments. They were fitted in several pong type consoles, although the 8610 is actually an improvement on the 8600 which itself was a later development of the 8500. Interestingly, a chap by the name of Cole is working an an FPGA emulation/recreation of said AY-3-8500 chip. See his blog here.

As a sidenote, the cartridges mentioned above most likely have other variants of these chips installed in them. From information on Cole's blog (actually at pongstory.com), there are also chips 8601 to 8607 all with different games baked into them..

Anyway, after putting this cartridge back together, out came the wire cutters and soldering iron. After a few minutes puzzling over exactly which connection would be the composite input to the modulator (it really shouldn't have been THAT difficult!) the mod was made but the question was, would it work?

So, we have power, we should have video and the only thing left to do was to switch it on and see if it would work.

BUT before we do - who the hell designed it so the power connector is the same type and size as the 'pistol' connector and are RIGHT NEXT TO EACH OTHER??

After making sure the power jack was in the right place....success!

Playing with..er..against myself.

Mrs Crashed loves how tidy my desk is.
Sort of. 

The video works without any problem at all and I'm really pleased with the output on my re-claimed laptop LCD panel.

But, the right stick doesn't work. And the 'programme' button doesn't either. Bugger.

A bit of fiddling and the programme button suddenly sprang into life. Probably just some more dust.. Cycling through the games was a trip down memory lane and an eye opener for my 13 year old who is more used to 3D open world shooters (yes, Fortnite). When I say 'eye opener' what I actually meant was that he rolled his eyes at my cackling at getting this partially working.

Anyway. The joystick. On this model the joysticks are actually connected via a DIN plug into the top of the console. Other Interstate consoles, those that did not use separate cartridges, had their joysticks or paddles wired directly into the main unit. They all use a handy storage system where they click into place on the case though, which I actually quite like.

The construction of the joysticks is fairly crude but they are analogue sticks. Two potentiometers are mounted at right angles and the movement of the stick is translated via a simple gimble. The fire button is a standard momentary push switch. The left joystick works without any problem except for the fire button being a bit sticky. The right joystick did not. It would occasionally show up and down movement but there was no left/right movement at all.

Dismantling the faulty stick completely, revealed that the potentiometers had some corrosion (liquid ingress maybe?) and so were unlikely to work ever again...

(Yes, I can see a wire's come off!)

Potentiometer separated
What to do? Well, they seemed to be 100K ohm pots and I did have some of a similar design. Sadly, they didn't fit and I think the ones I had were linear rather than logarithmic. I managed to wire them up on a breadboard and manually twiddle the pots but, apart from being not a great way to play a game, they just weren't quite right.

The problem is that pretty much all of the games on this thing require two players so only having one working joystick leaves it pretty useless. So I have taken a gamble to bag some spare parts. I have got a cheap Interstate console on the way via eBay. It's not the same model BUT it does use the same joysticks. Its an Interstate 1110 whereas my unit is an Interstate 1125.

Next time... we find out if the joysticks really ARE the same.


Crashed said...

Testing the comments section following the removal of G+. Nice one Google.

Crashed said...

Hmmm, no reply option...