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• How We Got Here

  Dzmitry Dydyshka • 3 days ago • 0 comments

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  Pro"log"ue

  We keep coming back to the same starting point: a bench PSU that already does its one job well. It supplies voltage, it supplies current, and it's been sitting on the bench doing exactly that for years. The problem was never the PSU — it's everything around it. Watching it means standing there. Logging it means writing numbers down by hand, or propping a phone up to film the display. Automating it usually means buying a whole new instrument and retiring the one that already works.

  We didn't want to go that route, so this project started small and has been growing outward from that one decision since.

  Extend, don't replace.

  A programmable PSU solves remote control by replacing the instrument you already own — that's the default answer, and it means the supply you already know, already trust, already paid for, goes in a drawer. We want the opposite: keep the PSU right where it is, and extend it in place instead of swapping it out. That's the constraint everything else here has to work around.

  And it shouldn't be locked down.

  Fine — but if we're keeping the PSU, we're not going to hand anyone a closed box either. A lot of "programmable" gear ships with closed firmware and a fixed feature set: whatever the vendor decided you get is what you get. That's not extension, that's a different flavor of lock-in. So the hardware, the firmware, and the software all stay open.

  So it should speak SCPI.

  Open is good, but open and mute doesn't help anyone driving a test bench. It needs to speak SCPI — the command language real instruments use for remote control. Give it SCPI over USB, then. Done?

  Not quite. We add TCP too!

  Most SCPI-capable gear is USB-only, or LAN-only — pick a lane and stay in it. We didn't see a reason to pick one. The same commands work whether you're plugged into a laptop on the bench or reaching the module over Wi-Fi from across the room.

  Control isn't enough — make it automatable.

  SCPI commands get you remote control, but remote control by hand is still someone standing at a keyboard instead of standing at a bench — that's relocation, not automation. On top of the commands, there's a scripting IDE and reusable dashboard widgets: something that runs a sequence and shows you the result, instead of waiting for you to type the next line.

  And don't stop at this one PSU.

  Once those widgets exist, why should they only know about this one instrument? They don't — they adapt to other SCPI-capable gear too. 

  Somewhere along the way, the project stopped being about one bench PSU at all, and that's still where the scope keeps expanding.

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  What PSU-EXT Is: One Module, Firmware, and a Dashboard

  Concretely, here's where that thinking has landed so far. PSU-EXT sits inline between a bench power supply and a load, measures voltage, current, and power, and controls the output path with a relay. That's the current physical shape the five points above have taken.

  "PSU-EXT" isn't just that board, though — it's three pieces that work together, each its own repo:

  - Hardware — the module itself
  - Firmware  — runs on the module
  - Software  — the companion stack that talks to the firmware over USB or the network

  Separate repos, one product, moving in parallel.

  Here's what it's built on right now:

  Operating range	0–25 V, 0–2.5 A
  Board size	100 × 50 mm (3.94 × 1.97 in)
  Control connection	USB-C (power and data)
  Controller	Espressif ESP32-S3
  Measurement front end	ADS1115 ADC + INA240 current-sense amplifier
  Isolation	Isolated I²C bus + isolated DC-DC (measurement domain)

  PSU-EXT Board

  And here's what runs it today:

  Capability	What it provides
  Firmware & software	Open hardware, firmware, and software — not closed or vendor-locked
  Control transports	SCPI over both USB CDC and Wi-Fi/TCP
  Automation	Built-in scripting IDE and reusable dashboard widgets
  Instrument scope	Widgets adapt to other SCPI-capable gear too, not locked to this one instrument

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  What...

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