---

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.

---

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

---

Every beat above leans on one word: extend. What that actually means in practice depends on who's using the extended PSU.

For makers and hobbyists, it's shaping up mostly as a second life for a PSU that's been sitting unused since something nicer came along. Extended in place, it comes back into rotation with capabilities it never shipped with — voltage, current, and power visible in a browser dashboard for a demo, livestream, or project video, or sitting between a battery and a load to watch voltage, current, and power fall through a discharge cycle.

For repair engineers, that same extension shows up as a controlled inline gate between the PSU and the device under test: set over-voltage and over-current behavior first, then switch the output on from the browser instead of reaching for the supply's front panel.

For more advanced engineers, extension is pointing toward an ecosystem rather than one instrument. The dashboard widgets aren't hard-wired to this one PSU — they adapt to other SCPI-capable gear too. Where that goes next is still open: the same scripting IDE and dashboard could in principle pick up a second instrument alongside it — a SCPI-capable electronic load, a signal generator, or a second PSU-EXT module on another rail — though the widgets don't ship pre-wired to any of those specifically today.

---

We're going to keep logging this project as it moves forward, not just posting once and going quiet. Future entries will share the insights and progress updates as we get them, the problems and setbacks we run into along the way (not just the parts that went smoothly), real use cases as people put PSU-EXT to work, and the engineering and science behind specific decisions we've made — plus general behind-the-scenes updates on where things stand. We don't have a fixed list of what's coming next or when — this is a running log, and we'll fill it in as we go, including more on the open-source side of things (the three repos, the contribution process) as that keeps developing.

---

If you're interested in PSU-EXT, subscribe to our pre-launch page on Crowd Supply: crowdsupply.com/maxeelabs/psu-ext