Re: [PiDP-11] My PiDP :)

[Bob Darlington]

Looks great, Nick!

I 3D printed an extension for the back of mine.   That let me fit in all the cables I wanted to add.   The extension has feet so you lose the original look of the PiDP, but it works for me.   Mine is mostly a decoration, but it's functional.   I went all out on my -10.  It has  a Pi 5 on there with a 1TB NVMe drive.   And since it's on full time blinking away, I figured why not have it do something else.  It's my home Plex server (serves movies/tv shows to our "i things" and TV.   I was using my PiDP-11/70 for a long time as a dev box, but it's been running so long that I need to do an OS upgrade (new install).  I'll get around to it eventually. 

Have fun with yours!   

-Bob

On Sat, Dec 27, 2025 at 10:50 PM Nick M <nicholas...@gmail.com> wrote:

I got my PiDP-11 :) Had to wait a day to build it, but finished it around 3 am Sat morning.

What a blast! I love all the options that are available to the user: power-key options, access to I2C/GPIO-19, terminal options, and so on. I've been using the virtual console for a month or so, which has been great, but flipping actual switches is just awesome!

Had some (mis)adventues on the way (that's what makes it extra fun) :

• despite all the warnings, I neglected to insulate the top of the Pi from the circuit board while testing it. I plugged the board in, saw lots of space, and thought "Oh, no way that will short anything" but of course the board moves without the standoffs, and it shorted, and I burned two LEDs. Easy to swap out (thanks for all the spare parts Oscar!)
  
• the rotary switches operated backwards. I scratched my head trying to figure out how I could have done that, then checked the group and of course this is well-documented, along with the easy fix.
• Address but 21 didn't work. Being the MSb, I assumed it was a software thing, but eventually looked closely at the board, and that switch's diode had one side left unsoldered. Another easy fix :)
• the RPi (3B) seemed to lag/hang on interactive Bash sessions while the panel was running, which hadn't happened before connecting the panel. But for whatever reason, even after disconnecting the Pi from the circuit board, it would still lag/hang. Switched to a RPi 4, problem mitigated, mystery remains.
• THE BAD ONE: even though I read about cleaning the switch contacts before soldering, I neglected to check them out and clean them as necessary. I was so focused on getting the switches lined up that I completely forgot about that. The switches ended up nicely lined (the switch template was a huge help), but soldering them took a lot of heat/time/solder, and sure enough, I cooked my Exam button :( It worked, but would fly through 3 or 4 consecutive addresses each time I pressed it. Sure enough, the top contacts are always connected, regardless of switch position. Fortunately, there's a bit of an intermittent spot when I flip it, and it very briefly disconnects, which is why it's doing the examine function at all. I added a software debounce to realcons_console_pdp11_70.c and it works well now, but it's not a permanent solution. Waiting to hear on ordering a replacement switch. I'm also wondering if the intermittent switch might be triggering RPi interrupts. As far as I can tell. the pi is polling the switches rather than using interrupts, but I didn't dig that deeply into the code.

I stained the base this morning, and it looks great. I like the alternate bases/mounting options others have come up with though, and may consider alternatives down the road. For now it's just sitting on my desk, happily running RSX11 and blinking away!

 Cheers, -Nick

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