*tiny Invaders Part 3

Endgame

As you can tell from the subtitle, the project is finished. Well, nearly…

If you can recall from the end of the last blog entry, I wasn’t happy with the look of the screen bezel panel. It needed the bolt holes masking some way (probably P45 body filler) and painting with some kind of textured paint. I went out and bought some good ol’ Hammerite ‘hammered’ finished paint and also some holographic glitter (black) spray paint.

I used neither of these (but please be aware, I will in future tinkerings). I fashioned up a new and improved 3D model of the screen bezel with features on the back and front and 3D printed it. I printed it face down on a textured print mat and it looks the business. I also made a 1mm deep recess in the front face around the curved CRT opening aperture, to fit a smoked perspex cover piece. Arcade machine manufacturers used to do this back in the day to hide imperfections and also dim down the glare of the CRT a bit (I guess). It also hides CRT scan lines, but I want to SHOW THEM OFF!

Please note the obligatory static perspex dust. Dagnabbit, this stuff is awful for static detritus…

I also added some coloured gel strips to the CRT tube to add some lines of colour, just like the original 1978 machines did. The smoked perspex also hides the obvious coloured ‘tape’ really well and enhances the effect. You’ll see this in a later video of me actually playing this little machine.

Below is a peaceful video of the milling of the smoked perspex. Aaaaand relax…

I also ordered some black anodised countersunk screws to hold the CRT tube to the bezel, but ended up not using them, as I preferred the stainless steel dome head screws, which I also used to hold the control panel down. We use these kind of screws quite a lot in the engineering profession and I also use them quite a lot in my joystick builds. A power jack socket was added to the back panel and I also added something that was painfully missed from the offset - a bloody start button! You can’t start smashing invaders up without a start button!!!

Lucozade in the background was keeping me alive during a nasty bug. Sniff, cough, ouch! (most things were hurting throughout this illness)

Mo’ problems

When I was wiring everything up and assembling and hot gluing everything inside I realised two things.

• One - why do I do such stupidly tight, fiddly things for projects?

• Two - The picture via composite was awful. This needed investigation.

The video works like this -

The game PCB outputs Red, Green, Blue signals, negative composite sync and Ground. 5 wires. These are fed into a small converter board which then outputs a composite signal and ground. This finally goes into the composite input of the travel TV.

I removed the jack from the converter PCB, as it was in the way of something on assembly and soldered the wires directly to the PCB traces. The other end of the 2 wire cable was soldered to the tabs of the socket on the TV (Signal and Ground - inner and outer of the socket)

This gave the game a horrible picture. Distorted, wobbly and more grey back ground than black. Simply unacceptable. Even worse than an RF signal (BOAK)

Before I removed the composite plug from the converter pcb, I was using a standard composite cable between converter and TV fro testing and the picture was as good as you can get it. It was baffling me why I was getting such a bad picture, when the wires were going to the same place as they have always gone, albeit soldered rather than a made up cable???

I fired off a question about this to a friend who is an expert with old arcade machines and especially B&W TVs and monitors. Smarty Martin got back to me the next day (he was at a Jesus & Mary Chain gig at the time - good show!) with a few ideas. I was sort of leaning the same way Martin had sent me and removed the socket from the TV chassis and soldered the wires directly. This now worked fine -

BIG SIGH.

Weirdly enough, even plugging something into the composite socket that wasn’t attached to anything sorted the picture out. I’m thinking it must be a grounding issue or some sort of interference? If anyone can shed light onto this, I’d love to be enlightened.

After, thankfully getting around this video problem (thanks Martin!) I pushed and shoved (and swore a bit) and got everything inside. I even added a speaker for some THUMP THUMP PEW PEW audio action into the roof of the box. It sounds good through the wood.

Apart from some nice chunky rubber feet to raise it up a bit and a CNC milled boiler plate to go on the back, this is DONE.

I’m not to happy about the hot glue holding the speaker, as if it ever fails, I wouldn’t want the magnetic speaker falling onto the tube. I think I’ll 3d print a bracket to hold that in place with dependable screws. Yes, I’ll do that in a minute…

One glaringly obvious omission is T-moulding. The is the protective plastic strip that covers the sides of the machine. I have the special T-moulding router bit to cut the grooves, but I don’t have a router table…

SIDE QUEST! - ROUTER TABLE

Hopefully I’ll have this up and running in the new year. I may have to take it to work and make it on a proper big machine. I have also ordered some 12mm black T holding. A stupidly small amount, obviously…

If you fancy making something like this yourself, I’d be happy to share drawings, 3D models, BOM etc. Just fire me a request in the comments.

Conclusion

Good points -

• It works!

• Boots immediately into the game (no emulation)

• Everything fitted into the (redesigned) case

• Has a working CRT!

• Nice gel coloured effects on the tube, like an original

• Runs off any 12v DC barrel jack power supply (centre +)

• HOT GLUE!

Bad points -

• Has some gaps in the case, due to slightly warped material

• Soldered cables inside rather than plugs ‘n’ sockets

• Fitting of the smoked perspex screen cover could have been neater

• Lack of t-moulding (this will be fixed)

• Needs an on/off switch

• Needs a volume control

• HOT GLUE!