Raspberry Pi telemetry
CPU load
--%
CPU temp
-- °C
CPU freq
-- MHz
Memory
--%
Disk /
--%
Load avg
--
Uptime
--
Network
--
Power / throttle
--
Stepper control
Position
0.0 °
0 rev · 0 pulses
State
disabled
idle · CW
Off = constant speed (reliable at any speed, incl. very slow). On = ramp start→speed→start to push the cruise toward the 1200 ceiling.
Jog (degrees)
G-code
—
no g-code run yet
Supported: G0 G1 G4 G90 G91 G92 M17 M18 M84 M0 M2 M30,
axis word X/A in degrees, F in deg/min.
Comments ; and ( ).
Wiring — RPi3 40-pin header → A4988 module (STEP / DIR / EN)
Highlighted pins are used. View it physically: pin 1 is top-left (nearest the SD card / inner corner).
| A4988 control | RPi BCM | Phys pin | Note |
|---|
Logic supply — REQUIRED, separate from VMOT: A4988 VDD = 3–5 V from the RPi
3V3 (pin 1) or 5V (pin 2). Without VDD the chip is dead — STEP/DIR are
ignored and the motor draws 0 A.
Motor power (separate from logic): A4988 VMOT = 8–35 V supply, GND to its ground. Put a ≥100 µF electrolytic across VMOT/GND close to the board.
RESET ↔ SLEEP: tie these two A4988 pins together (jumper). Left floating, the outputs stay disabled and it will not step.
US-17HS4023 coils → A4988 outputs: coil A → 1A / 1B, coil B → 2A / 2B (typical 4-wire: A = black/green, B = red/blue — verify against your unit).
Current limit: set Vref ≈ I × 8 × Rcs. For 0.7 A and Rcs = 0.1 Ω, Vref ≈ 0.56 V — start lower and tune.
EN is active-LOW; the app drives it HIGH (disabled) on boot for safety.
Common ground is mandatory: tie RPi GND ↔ A4988 logic GND ↔ 12 V supply (−) ↔ VMOT GND to one point.
Motor power (separate from logic): A4988 VMOT = 8–35 V supply, GND to its ground. Put a ≥100 µF electrolytic across VMOT/GND close to the board.
RESET ↔ SLEEP: tie these two A4988 pins together (jumper). Left floating, the outputs stay disabled and it will not step.
US-17HS4023 coils → A4988 outputs: coil A → 1A / 1B, coil B → 2A / 2B (typical 4-wire: A = black/green, B = red/blue — verify against your unit).
Current limit: set Vref ≈ I × 8 × Rcs. For 0.7 A and Rcs = 0.1 Ω, Vref ≈ 0.56 V — start lower and tune.
EN is active-LOW; the app drives it HIGH (disabled) on boot for safety.
Common ground is mandatory: tie RPi GND ↔ A4988 logic GND ↔ 12 V supply (−) ↔ VMOT GND to one point.
Microstep DIP (A4988 MS1 / MS2 / MS3)
| Microstep | MS1 | MS2 | MS3 | steps/rev |
|---|---|---|---|---|
| Full (1/1) | OFF | OFF | OFF | 200 |
| Half (1/2) | ON | OFF | OFF | 400 |
| 1/4 | OFF | ON | OFF | 800 |
| 1/8 | ON | ON | OFF | 1600 |
| 1/16 | ON | ON | ON | 3200 |
DIP ON = HIGH (sw1→MS1, sw2→MS2, sw3→MS3) — verify your board's silkscreen.
After changing the DIP, set the Microstep control above to match and re-zero, or the degree readout drifts.
Speed is microsteps/s, so rpm = pps·60/(200·microstep) — higher microstep = smoother but lower top rpm at the 1200 pps cap.