Description

 

Wire it like a relay deck — +V to one input spins the motor one way, +V to the other input spins it the other way, both off stops it. Drive it from a DPDT switch, a flap controller, an R/C receiver, or a Garmin GSA 28 trim output. The board doesn’t care where the signal comes from.

 

Why not just use a relay deck?

 

Relay decks are consumables and most builders don’t realize it until one fails. The contacts arc on closure from motor inrush, arc again on opening from inductive back-EMF, and one day the silver-alloy contact material has migrated enough that the relay either welds shut (runaway motor) or pits open (no motor). It’s a question of when, not if.

 

Mechanical relays also can’t follow PWM. The GSA 28’s airspeed-scheduled trim — where the servo modulates duty cycle to reduce trim authority at cruise — gets thrown away the instant a relay touches the signal. Relays just buzz or burn out.

 

The V8 replaces the whole relay deck with four MOSFETs that don’t arc, don’t wear, don’t click, switch in microseconds, and follow PWM faithfully end to end.

 

Why not just use a cheap H-bridge motor controller?

 

Because most of them are built for 12 V hobby use and will quietly die in a 24 V aircraft system. Specifically:

 

They use ±20 V VGS MOSFETs. In a 24 V H-bridge, the gate-to-source voltage equals the supply rail. Add 28 V alternator overshoot and inductive ringing and those parts are past their absolute maximum gate-oxide rating under normal operation, before any transients. They’ll work — for a while — then the gate oxide punches through with no warning. This board uses FQP17P10 and PHB29N08T, both rated VGS ±30 V. Specifically picked for 24/28 V buses.

 

They need a separate logic supply. Most generic H-bridges want 5 V or 12 V logic and a separate motor rail. The board takes 6–30 V on both sides and decouples them — drive a 24 V motor from a 12 V signal, or vice versa, with no losses.

 

They have a microcontroller in the signal path. Boot delay, firmware bugs, watchdog resets, potential for getting bricked. This board has no MCU, no firmware, no software at all. Pure analog signal chain. It cannot be bricked because there is nothing to brick.

 

Specs

 

6–30 V input (recommended 12–28 V) · up to ~5 A continuous per channel · dual-channel optocoupler isolation · TVS rail clamp (lightning protection module) · ~95 × 35 mm · −40 to +85 °C · two pluggable terminal blocks · pure analog signal path, no microcontroller.

 

What you get

 

Assembled board, full schematic, PCB gerbers, JLCPCB-ready BOM, Falstad simulation file, and an installation manual that documents the design at the stage level — including GSA 28 wiring, shielding rules, breaker sizing, and bench bring-up procedures. Open source for personal and educational use. Commercial licensing available.

 

Designed and documented in the USA by Novabox LLC — novabox.works

 

This board is experimental/hobbyist hardware — not TSO’d, ETSO’d, UL-listed, or approved for use in certified aircraft, medical devices, or life-safety systems. Installation and application are the user’s sole responsibility; Novabox LLC assumes no liability for use, misuse, or system integration.