Shim design

I was thinking back on the spring of 2017, and first time Oscar came over to my home and showed his PiDP-11 prototype. Already then the subject of a ‘shim’ came up… but we didn’t really reach a conclusion. Nor did we on later meetings…

It all seems so simple. The PiDP-11 has a connector, the FPGA board has a connector, and some peripherals need to be interfaced. But then the questions start… which FPGA board? how will the whole thing fit into the rear end of the console? which peripherals go on, and how will those fit in and how will things like Ethernet cables and sd cards come in to the console? Oscar’s initial idea was to make a board of the same size as the lid of the console box, and make a DE0-nano sized hole in it so you could still reach the switches on the DE0-nano and see the blinkenlights. And I wanted to try to include some kind of multiport usb-to-serial, because I was getting fed up with the amount of cables on my work desk…

We didn’t manage to reach a conclusion on that. As time passed, I did some experiments with my usb-to-serial idea and ordered a pcb for it – including component assembly, because I didn’t feel like soldering lots of tiny SMD. That was a lot of fun to do, and the board turned out nicely – with only one real mistake in the prototype: the connector for the PMODNIC was upside down. Or maybe the right way up, because – as I found out – it’s more logical to have the whole board upside down…

Anyway – in practice the board worked very well, but there were two things about it that I really didn’t like – to connect it to the DE0-nano and to the PiDP console you’d need two 40-pin ribbon cables; one even with a male connector on. Lots of work to make, unwieldy and adding quite a bit to the kit cost. And the other thing: stacked to the DE0-nano, it would stick out beyond the rear end of the PiDP-11 console box…

That was basically the end of the DE0 shim – a nice experiment, and I’m using them still for my test bench, but not for the PiDP console. I didn’t really decide not to continue with it, it was more a thing of waiting for the idea that would make it into a nice project again. But that idea didn’t really come.

Until the CYC-1000 arrived… but that’s the subject of tomorrow’s post.

prototype shim pcb for de0nano and pidp-11 console

Here’s one of the few remaining prototypes… two more are in use; actually, my always-on 211bsd system runs with one, and it would have had an uptime of over a year now if I hadn’t made a mistake with the FPGA software some time in January…

2 comments to Shim design

  • You don’t need a male connector on the cable. You can use a female connector and use a long-pin PCB mount male connector. Just slide the plastic grid of that connector toward the center of the connector, leaving an equal length of pins on either side. Then just plug one side into the cable and the other side into whatever female connector it should go into.

    • sytse

      Sure – and I’ve done that too. Or – even easier – just plug the male connector on the shim directly into the console. But the stack of de0nano and shim would stick out of the PiDP box…

      In short, I’ve played around with the different bits a lot, but none of the solutions I found was particularly elegant…