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Cartridge extender boards

Posted: Mon May 27, 2019 10:02 am
by sorchard
I just wanted to draw attention to the Coco/Dragon cartridge port extender boards available from Retro Innovations as I think they are extremely good value: ... nsion-pcb/

I recently bought two of these at $3 each, with just $2 shipping to the UK. Total cost to me was £6.35 and they arrived within two weeks. It looked like a sorting machine had tried to mangle the envelope, though the boards themselves survived unscathed as they were well wrapped inside.

The intended use is as an extender, presumably to gain access to the inside of a cart while plugged in, or as a Y splitter allowing use of two carts at the same time, providing there is no address clash, or as a means of turning key signals on and off via dipswitches. (So you could for example use it to prevent an autorun cart from starting up without having to modify the cart or cover the relevant contact with tape)

The boards are supplied bare, so you need to supply and assemble the components you need. Now where I think these could be really useful for development is if you solder a couple of pin headers to the board instead of a vertical edge connector. That would give you a bunch of handy connections into the Dragon for attaching logic probes or bread board circuits. This also turns the board into a re-usable prototype cartridge by attaching daughter boards via matching header sockets.

The photos below show a bare board, then with pin headers and switches soldered on, and finally a prototype board attached via the pin headers.

extender-bare.jpg (97.37 KiB) Viewed 2193 times
extender-pop.jpg (103.44 KiB) Viewed 2193 times
proto.jpg (169.42 KiB) Viewed 2193 times
combined.jpg (182.54 KiB) Viewed 2193 times

Re: Cartridge extender boards

Posted: Mon May 27, 2019 2:38 pm
by Bosco
Hi Stew.

I spy an SN76489. Is this a GMC equivalent cart?

Re: Cartridge extender boards

Posted: Mon May 27, 2019 4:37 pm
by sorchard
Hi Steve,

Well spotted, you're quite right; it's the audio part of the CoCo GMC. I made the board a while back but had it piggy-backed onto another cartridge, which proved to be a bit clumsy and fragile. When I spotted the extender boards from Retro Innovations I realised this was a way of making it more robust.

Re: Cartridge extender boards

Posted: Mon May 27, 2019 11:15 pm
by dlinsley
I'm going to order a couple to try and get the Sprite board going.

Re: Cartridge extender boards

Posted: Sun Jul 07, 2019 6:40 pm
by BluePilot
Hi David,

Thanks for selling me your spare extender board - really appreciated.