Mechanical Parts

A project log for Programmable Precision Resistor

A SCPI programmable precision resistor

sebastianSebastian 08/31/2023 at 20:020 Comments

After being asked about some aspects of the mechanical design and components used a few times, I'd like to address those questions. I have to admit that I'm neither very good at the mechanical design, nor do I have a 3d printer (yet) or a shop where I can do metal work myself. That being said, I was still able to design a reasonably professional looking device and bring it to life with the help of modern prototyping services.

The new 3D printed knob for the rotary encoder.

CaseELMA, Stylebox 15 Standard; 2 RU, 42HP (half 19")Very expensive for a typical DIY project, although I don't know the exact pricing
Front and Rear panels1.6mm Aluminium PCB with white solder mask and black silk screenSee next post for details
PCB mountingStand-offs (M3)Stand-offs are connected to chassis (earth).

However, the circuit is earth referenced via cable (connected to the power connector).
New Rotary knob3d printed (MJF)Most pictures were taken with the old temporary knob
Push buttonsC&K/littlefuse PVA series switches with matching capsDifferent force ratings available
Line switchC&K NE18 series switchCan be a pain to design and print a connecting rod if the switch is located far back in the unit.

I just used a thin wood rod and some tiny shaft coupling to connect the rod with the switch. Seems to work just fine.

A 3d printed part would be more professional, no doubt about it
Red filter for displayColor filter, Red foil, 0.3mm; random amazon product; glued to the back of the front panelWorks surprisingly well, however it's obviously not as strong as acrylic glas.

Reminds me of the HP/Agilent 66xx series power supplies (and other products) with the thin foil covering their LCD displays.

Wouldn't like that for commercial use at all ;) 

Next steps

There will be a separate post where I explain the fairly straight forward process of designing the front and rear panels.