Barnacle mod

What it is

The Stamp-P4 takes over motion. Three wires (A, B, GND) carry A/B quadrature from the P4's LP core to the motor's pulse and direction inputs. On a stock R+D build the motor connects to J12, the 4-pin header (PU+, PU−, DIR+, DIR−), plus power on J2. On the barnacle J12 stays empty.

Five more wires go to J8 on the R+D board, a 10-pin header that is normally unused; the barnacle uses it for the P4 link: 5 V, GND, a serial link each way, and TRIP. The WROOM runs the shim firmware. It reads motor current, motor voltage and the button, drives the RGB LED, and reports to the P4 at 115200 baud.

Motor power stays on J2 SERVO POWER. The current sensor sits in that path, so the helper sees motor current only while the motor draws from J2.

Stopping the machine

The R+D board has no motor power switch and no Modbus link to the motor. In this build, the motor's enable line, ENA, is unconnected. Software cannot cut motor power.

Two things stop the motor: the P4 stops its A/B output, or the E-stop cuts power. Wire the E-stop as the reference build does. Use a latching switch that breaks the AC mains to the power supply (step 6).

Overcurrent protection stays with the motor. The current and voltage the helper reports are for monitoring and homing.

Parts

Tools

• Soldering iron and solder.
• Wire strippers.
• A multimeter with a DC milliamp range.
• A computer, a USB-C cable and the USB to RS485 adapter.

Build

0. Set up the motor

The R+D board has no Modbus link to the motor. Set up the motor first, over its own RS485 port (Modbus RTU), with the USB to RS485 adapter. Caution: the motor misreads quadrature in pulse and direction mode. Set the command input to A/B pulse input.

The motor setup tool finds the motor at 9600, 19200, 38400 or 115200 baud and applies the barnacle's settings. It runs in Chrome or Edge on a desktop. It is a work in progress. Unplug the adapter when you are done: the barnacle does not use RS485.

1. Flash the firmware

Flash both boards before any wire goes on, from the web flasher in Chrome or Edge on a desktop. The flasher loads the newest release. On a board that is already wired, disconnect the wires from J8 first.

1. Flash the WROOM over the R+D board's USB-C, with nothing else powering the board. Open the flasher's Helper card. Use barnacle-shim 0.1.82 or newer. After this, the WROOM needs USB only for recovery.
2. Flash the Stamp-P4 over its own USB-C. Open the flasher's Barnacle card. It loads nucleus-p4b. To have it join your network on first boot, fill in Pre-program Wi-Fi before you write.

Later updates go over the network from Phosphor. On the machine's System page, the Firmware card takes the release's app image (nucleus-p4b-version-app.bin, from the release on GitHub). Press Update. Then double-press PAIR at the machine: on the barnacle, S2 on the R+D board.

Each nucleus-p4b image carries the WROOM's firmware. When the WROOM runs any other build, the Stamp installs its copy over J8. The install starts as soon as no motion runs and takes about 40 s (an estimate, not yet measured). The machine loses its home position when the update starts: home the machine again when the update finishes. Motion started during the update stops the update. The WROOM keeps its old firmware, and the update starts over once motion stops. A WROOM on a barnacle-shim release older than 0.1.82 cannot take updates this way. The machine logs that and works as before until you flash the WROOM over USB once.

2. Prep the Stamp

Plug the Stamp-AddOn C6 into the SDIO connector, at the lower left of the Stamp's top side, beside the USB-C.

Find pad 1: top left, at the camera connector end. The left column runs 1 to 19, top to bottom. On that column the odd pads are through-hole and the even pads are castellated only. The wiring uses the through-hole pads, so it solders like any through-hole part.

Pad 15 is the Stamp's USB-C VBUS. From there, 5 V passes an overvoltage switch (AW32901) and a CH213K ideal diode to the module's 5 V rail. An SY8089 buck, rated 600 mA, makes 3.3 V. So 5 V can come in on pad 15.

3. Connect to the Stamp

1. Bring the wires, or a 7-pin header, in from the back of the Stamp. Put them into pads 7, 9, 11, 13, 15, 17 and 19. On the top side a header body would sit on the SDIO connector.
2. Solder from the top.
3. Check for bridges to the castellated pads between them: 8, 10, 12, 14, 16 and 18.

The through-hole pads sit 2.54 mm apart. A 2.50 mm pitch header also goes in: over 7 pins each end pin sits 0.12 mm off its pad's center.

4. Wire the motor

Three wires from the Stamp to the motor's signal input.

• Connect pad 9, A, to PUL+.
• Connect pad 11, B, to DIR+.
• Connect pad 13, GND, to PUL− and DIR−, jumpered together at the motor.
• ENA, ALM and PED stay unconnected.

The motor's opto inputs take 3.3 V straight from the P4, with no level shifter. That works on the bench and over 3 m of shielded Cat5 from an ESP32-S3. The P4's pins drive the same as the S3's: 20 mA by default, 40 mA source and 28 mA sink at drive strength 3.

Pad 13 takes two ground wires, this one and the one from J8 pin 1. Put both in the pad, or splice one onto the other close to the Stamp.

5. Wire J8 on the R+D board

Five wires from the Stamp to J8. J8 is normally unused on the R+D board; its connector is on the back.

J8 pins 7 and 9 sit between 5 V pins (6, 8 and 10). A wire one position off puts 5 V on a P4 pin, and the P4 does not survive it. Measure before the wires reach the Stamp (step 7).

Fit the capacitor at the Stamp end, across 5V and GND. Keep it within a few centimeters of pads 15 and 13. Connect its negative lead to GND. The capacitor supplies the Wi-Fi transmit bursts.

6. Wire the E-stop

Put the latching E-stop in the AC mains feed to the power supply, as on the reference build. Pressing it powers down everything: the motor, the R+D board and the Stamp. The P4 boots unhomed when power returns, so you home again before the next run. Keep the motor's DC supply on J2 SERVO POWER: the current sensor sees only what flows through it.

7. Pre-power checks

1. With nothing powered, check continuity on every wire, end to end, against the point-to-point table.
2. Check for shorts between neighboring Stamp pads, most of all 15 (5V) and its neighbors 13 (GND) and 17 (TX).
3. With the wires not yet on the Stamp, power the R+D board. At their Stamp ends, measure to GND: the 5V wire reads about 4.5 V. TX, RX and TRIP read 3.3 V or less. Anything near 5 V on a signal means a wire sits on the wrong J8 pin.
4. Confirm the motor is in A/B pulse input mode (step 0) with ENA, ALM and PED unconnected.

8. First power-on and current check

1. Unplug USB-C from the Stamp.
2. Connect the wires to the Stamp with the meter's milliamp range in series with the 5V wire.
3. Power the R+D board. Read the Stamp's draw with Wi-Fi active. Expect about 350 mA average, with bursts near 600 mA. If the draw is well above that, the R+D 5 V rail has no room left. Stop and find out why.
4. Take the meter out, reconnect the 5V wire, then power the motor.

Before the first run, confirm jog speed, jog accel and input jerk once in Phosphor's Setup, then home.

Reference

Point to point

R+D J8 pinout

J8 is a 10-pin header, normally unused on the R+D board; pin 1 is the square pad. In and out are from the WROOM's side. Q3 to Q5 are BC817 transistors with 220 Ω base resistors. They only sink, and their collectors are the minus pins.

WROOM helper pin map

The shim leaves UART0 (IO1, IO3) alone. The CP2102 owns it, so the WROOM still flashes over the R+D board's own USB-C.

Power budget

The Stamp takes 5 V from the R+D board's 5 V rail: an LMR14006 buck rated 0.6 A, after a B1100 Schottky diode, so about 4.5 V at J8. The board's own loads share it. These numbers are estimates; step 8 measures the largest.

The average fits. The 220 to 470 µF capacitor at the Stamp carries the short peaks.

Do not power the Stamp from the R+D board's 3.3 V. That rail comes from an ME6211C33 regulator in SOT-23-5, which would dissipate about 0.4 W at the Stamp's load, more than that package can shed.

Pad 15 is the same net as the Stamp's USB-C VBUS. With the J8 wires connected, a computer on the Stamp's USB-C also powers the R+D board's 5 V loads. Disconnect them before you flash over USB, or update over the network from Phosphor (step 1).

How the link works

The link uses only parts already on the R+D board.

• TX, P4 to WROOM: the P4 drives J8 pin 2 directly. On the board that is the old ALM input, a 10 kΩ pull-up to 3.3 V into WROOM IO13. Plain 3.3 V UART.
• RX, WROOM to P4: the WROOM's UART TX on IO14 drives Q5, whose collector is J8 pin 9. The transistor inverts, so the shim inverts its TX and the wire carries normal UART. The link runs at 115200 baud: the internal pull-up is weak, and that rate leaves wide margin on the rising edges while still carrying current and button data at 500 Hz.
• TRIP: the WROOM drives Q4 from IO27, whose collector is J8 pin 7. On a current spike, the end stop during homing or a jam, the WROOM pulls TRIP low and the P4 stops on its next tick without waiting for the serial link.
• While the WROOM resets or boots, IO27 floats, Q4 stays off and TRIP reads high: not tripped. A helper that hangs with IO27 high holds TRIP low, and the machine stops.
• J8 pin 4 (WROOM IO4, input) and pin 5 (Q3, from IO26) are spare.

Troubleshooting

The Stamp does not power up

Measure pad 15 to pad 13: about 4.5 V. No voltage: check the wire on J8 pin 10 and the GND wire to J8 pin 1.

A signal wire reads near 5 V

It sits one position off on J8, onto pin 6, 8 or 10. Fix it before the Stamp goes on.

The motor does not move

Check the motor is in A/B pulse input mode (step 0) and that PUL− and DIR− are jumpered to GND at the motor.

The motor runs the wrong way

A and B are swapped. Swap the two wires at the motor.

TRIP reads tripped all the time

With the helper running, J8 pin 7 idles at 3.3 V. Low: the shim holds IO27 high or has hung, or the pin 7 wire is wrong.

No data over the link

Check that TX on pad 17 connects to J8 pin 2. Check that RX on pad 19 connects to J8 pin 9. Both ends run at 115200 baud. The shim inverts its TX.

Motor current reads zero

The motor draws its power from somewhere other than J2. Move the motor power connection to J2 SERVO POWER.

A home is refused before it moves

The helper reads current with the motor at rest, or has no current zero yet. It takes the zero with the motor still, about 4 s after power-on. Power-cycle the R+D board with the motor still, then home.

A home fails: the link to the helper is lost

The link to the WROOM stopped during the home. Check the wires on J8 pins 2 and 9, then home again.

The Stamp resets when Wi-Fi transmits

The 5 V sags on transmit bursts. Check the bulk capacitor is fitted at the Stamp end and its polarity is right.

The R+D board lights up while you flash the Stamp

USB-C on the Stamp feeds the R+D 5 V rail through the 5V wire. Disconnect the wires to J8, or update over the network from Phosphor.

The WROOM will not flash

Flash it over the R+D board's USB-C. The CP2102 there owns UART0. The web flasher has a Helper card for it.