Four tone driver

Six fan driver, rev A

An Arduino Nano carrier board with six low-side MOSFET fan channels. four-tone uses four of them; the other two are spare for other projects. It is designed for JLCPCB fabrication and assembly, and rev A was ordered on 2026-09-15.

The KiCad files keep the project's original four-tone-driver name; the board itself is titled "six fan driver". Every symbol carries its JLCPCB/LCSC part number in an LCSC field.

BOM

Availability was checked on 2026-09-15 through tscircuit's jlcsearch mirror of the JLCPCB catalogue, and every line was in stock. Stock changes, so re-check in JLCPCB's BOM tool when ordering.

Circuit

• Power, J1: pin 1 +12 V, pin 2 GND, pin 3 +5 V, pin 4 GND. The two grounds are joined on the board, so the supply's 5 V and 12 V returns must be common. Confirm this with a meter before connecting (see the build guide).
• Logic power: +5 V feeds the Nano's +5V pin directly through the socket, bypassing its regulator. VIN is not connected. The Nano reference design has a Schottky diode on USB VBUS, so the supply cannot back-feed a computer while USB is plugged in for programming. Clones vary; check the ones you use.
• Each fan channel: a Nano PWM pin drives the AO3400A gate through 1 k, with a 100 k pull-down to GND so the fan stays off while the Nano resets or is unplugged. The MOSFET switches the fan's return (connector pin 2) to GND. An SS14 across the fan clamps the lead inductance. A red LED with 4.7 k from +12 V to the switched return lights when the channel is on (about 2 mA) and follows the PWM ramp. It lights with no fan plugged in, which helps testing.
• Fan connectors J11-J16: pin 1 +12 V (marked + on the silkscreen), pin 2 switched return.
• Current: the fans are rated 0.18 A. The design allows 0.5 A per channel for start-up and 3 A for all six. The AO3400A is about 30 mOhm at 5 V gate drive, so it dissipates under 10 mW per channel.

Channel to pin map

Channels follow the order of the pins along the Nano's header, so the six gate traces fan out without crossing. D13 is avoided: it has no PWM, and the bootloader flashes its LED at every reset, which would blip a fan.

Layout

• Board: 130 x 70 mm, 2 layers, 2 mm corner radius, M3 holes 4 mm in from each corner.
• Edges: fan connectors along the bottom edge, 19 mm apart, each channel's parts directly behind its connector. Power terminal on the left edge, wire entry facing out, +12 V at the top. Nano sockets along the top right with the USB end at the right edge.
• Nano sockets: J2 pin k is Nano pin k; J3 pin k is Nano pin 31-k. The placement was checked pad for pad against KiCad's Module:Arduino_Nano footprint.
• Copper: GND pours on both layers, stitched with vias. The Power net class (+12 V, +5 V, GND, FANn_DRV) uses 0.8 mm tracks with 0.25 mm clearance; everything else is 0.3 mm with 0.2 mm clearance.
• Silkscreen: board name and revision, the licence (CERN-OHL-S-2.0), and the source location github.com/ideocentric/four-tone, which CERN-OHL-S asks products to carry. The ensō house mark sits beside that block (source: ../art/enso-oro.svg). FAN1-FAN6 labels are on the board-edge side of the connectors with + beside pin 1, and an outline of the Nano's USB connector shows which way round the Nano goes.
• Checks: ERC 0 violations; DRC 0 violations, 0 unconnected, 0 schematic parity issues (KiCad 9.0.6).

Known limitations of rev A

• J1 footprint: the layout uses KiCad's Phoenix MKDS 1.5 5.08 mm footprint for the DB128V-5.08-4P terminal in the BOM (C2915641). Compare the hole size and body outline with the real part when the boards arrive.
• Brushless fans on PWM: 2-wire brushless fans have their own driver inside. Switching their supply with PWM can make them stall or tick at low duty, and the ~490 Hz PWM can be audible. The firmware only ramps briefly (250 ms), but test one fan before relying on low duty cycles.
• Fan lead length: the fans used here have 11" (280 mm) leads, so the board has to sit within about 250 mm of each fan once slack is allowed for.