The dive on every hole
The arc crosses a hole or an already-cut path, voltage spikes, and without anti-dive logic the torch slams straight into the workpiece.
Open source — GPL v3
A real Torch Height Controller for under 60 € of parts
SmartTHC is open-source firmware for Arduino Uno R4 that keeps your plasma torch at the perfect height — with an explicit anti-dive lift that saves your torch when the arc crosses holes and already-cut paths.
- PID control loop
- 1 kHz
- PID control loop
- anti-dive reaction
- ~120 ms
- anti-dive reaction
- total parts cost
- ≈ 40–60 €
- total parts cost
Cut demo video — coming soon
Tired of crashing torches into cut pieces?
If you run a DIY CNC plasma table without height control, you already know these three moments.
Ruined plates and consumables
One crash can kill a nozzle, warp a plate, or scrap an hour of cutting. On thin sheet it happens faster than you can hit stop.
Black-box THC units
Commercial torch height controllers cost 150–800 €, hide their logic, and when they misbehave you can only guess why.
Built for real workshop conditions
Every feature exists because something went wrong on a real cut. The full source is on GitHub — read it, audit it, hack it.
1 kHz PID height control
A tight PID loop reads arc voltage and commands the Z stepper every millisecond, tracking warped sheet in real time.
Explicit anti-dive Z lift
When arc voltage spikes over a void, the torch retracts fast — 3 mm in about 120 ms by default, fully parametrizable. No more torch crashes on holes.
Motion-gated activation
THC only engages once the table is actually moving at cutting speed, so the pierce phase never triggers false corrections.
Plasma-gated dual filtering
A fast EMA feeds the PID while a slow 200-sample average builds the anti-dive reference — only while the arc is stable.
EMI-proof watchdog
Plasma arcs are electrically brutal. A hardware watchdog timer recovers the controller instantly if interference hangs the MCU.
8-screen LCD menu
Tune setpoint, PID gains and anti-dive parameters live on a 16x2 LCD with a KY-040 rotary encoder — no laptop at the table.
Structured serial logging
key=value status lines and edge-triggered events you can grep or plot to understand exactly what the controller did, and why.
EEPROM persistence
Your tuned parameters survive power cycles with wear-friendly deferred writes. Metric or imperial units at compile time.
How SmartTHC compares
An honest look at the usual options for adding torch height control to a DIY plasma table.
| Solution | SmartTHC | Commercial THC box (150–300 €) | LinuxCNC THCAD setup |
|---|---|---|---|
| Price | ≈ 40–60 € of parts, firmware free | 150–300 € | THCAD card + PC + interface hardware |
| Anti-dive logic documented | Yes — full source and tuning guide | Proprietary, rarely documented | Configurable, steep learning curve |
| Hackable / open source | Yes — GPL v3 firmware | No | Software yes, hardware no |
| Standalone (no PC needed) | Yes — runs on Arduino | Yes | No — requires a PC |
| Community support | GitHub + Discord | Vendor support | Expert forums |
From parts to first cut in three steps
- 1
Flash the firmware
Clone the repo, build with PlatformIO and flash your Arduino Uno R4 over USB. Defaults are safe and bench-test ready.
- 2
Wire it per the guide
Follow the wiring diagrams: voltage divider to A0, A4988 driver to your Z stepper, LCD and encoder, gating signals from your table.
- 3
Cut
Bench-test the polarity checklist, then run a real job. Watch the anti-dive lift save your torch on the first hole.
Premium documentation
The step-by-step build guide
The firmware is free and always will be. The premium guide is everything around it: the exact hardware build, wiring and tuning that took months of workshop iterations to get right.
What the guide contains
- Complete hardware setup: every part, with links and alternatives
- Wiring diagrams for the Uno R4, A4988 driver, LCD, encoder and plasma divider
- PID tuning walkthrough with the serial plots to prove each step
- CNC controller integration: LinuxCNC, Mach3, grblHAL and FluidNC gating signals
- Bench-test checklist to verify Z polarity and anti-dive before any real cut
€20 One-time purchase — launch price until October 2026
Get the build guideBuy once, get lifetime updates by email.
DIY project involving high plasma voltages — build at your own risk.
Free download
The free THC cheat sheet
Wiring essentials, PID starting points and the bench-test checklist in one printable PDF. Free — your email is all it costs, and it only ever gets SmartTHC updates.
Download the cheat sheetDelivered via Payhip. No spam, unsubscribe anytime.
Frequently asked questions
Is it really free?
Yes. The firmware is open source under GPL v3: download it, build it, modify it — free forever. What we sell is the premium documentation: a step-by-step build, wiring and tuning guide that saves you the trial-and-error.
What tables does it work with?
Any CNC plasma table with a stepper-driven Z axis and a readable arc voltage signal. It was developed on a DIY table and is used daily in a professional workshop. RatRig Stronghold builds and homebrew tables are typical hosts.
Do I need a PC connected during cutting?
No. SmartTHC runs standalone on the Arduino Uno R4. Once your parameters are set, the controller handles height control by itself — your CNC controller keeps doing motion, SmartTHC keeps doing height.
What about my controller — LinuxCNC, Mach3, grblHAL, FluidNC?
SmartTHC doesn't replace your motion controller; it complements it. It reads the same gating signals (arc OK, THC on/off) and drives the Z stepper directly. The guide covers the integration wiring for the most common controllers.
Is high voltage involved?
Plasma cutters are high-voltage, high-current equipment. SmartTHC reads the arc voltage through a voltage divider — never wire the raw arc voltage into the Arduino. This is a DIY project involving high plasma voltages: build at your own risk, and follow the safety guidance in the documentation.
What do I get when I buy the guide?
A complete, illustrated build document: full parts list, wiring diagrams, firmware configuration, PID tuning walkthrough, controller integration and a bench-test checklist. Everything needed to go from parts on the bench to a working THC.
Do I get updates?
Yes. The guide is a one-time purchase and every future edition is sent to you by email, free. As the firmware evolves, the documentation follows.
What is the refund policy?
If the guide doesn't help you get your build running, reach out within 30 days and we'll refund you. Simple as that.