HeRo 2.0

Build guide

Solder the board

SMD first, then through-hole. The tutorial times this at about 20 minutes of reading and 130 minutes of building. Figures are from the HeRo V2 Robot Build Tutorial (v1.0, 27 Sep 2025).

Passives · ICs · LEDs · Connectors · IR sensors · 5 V boost · Checks

Work current-limited (≤300 mA) until the smoke test. Treat the Li-Po as a live cell once it is connected.

Tools for PCB work
Bench tools.
Populated HeRo board
A finished board.

BOM on the board

  • Passives: R0–R8 (4k7), R9 (0 Ω), R10 (18 Ω), R15 (0 Ω), C1–C2 (100 pF). R11 is not mounted.
  • Indicators: LED0–LED1 (WS2812B 5050). Optional charger LEDs: STDBY green 0805, CHRG red 0805.
  • ICs: IRLML2502 (SOT-23), CD4051 (SOIC-16), TP4056 (SOP-8, optional charger).
  • Sensors: TCRT5000L ×8.
  • Connectors: two JST-PH-2, 1×4 female (I²C/UART), four 1×3 male (E/M), two 1×16 female (ESP), slide switch.
Blank HeRo PCB
Blank HeRo v2 board. Order Gerbers from the previous step if you do not have one.

Soldering order (SMD → THT)

About 90 minutes on the iron

1. Small passives — C0603 then R0805 (C1–C2; C3–C4 optional; R0–R10, R12–R15). Leave R11 empty.

SMD capacitors
Capacitors.
SMD resistors
Resistors.

2. ICs — TP4056 if you want onboard charge, then CD4051, then IRLML2502. Pin-1 / orientation dot to the silkscreen. Inspect bridges.

IC soldering
ICs on the board.
IC orientation
Match the pin-1 mark.

3. Addressable LEDs — WS2812B, arrow DIN → DOUT, polarity to silk. Continuity-check the pads.

WS2812B LEDs
WS2812B orientation.
Status LEDs
Optional STDBY / CHRG LEDs.

4. Connectors and switch — JST-PH-2 ×2, I²C/UART header, encoder/motor headers, ESP sockets, slide switch.

Headers
Headers.
Switch and sockets
Switch and ESP sockets.

5. IR sensors — eight TCRT5000L, same standoff, coplanar, gap aligned around the ring.

TCRT5000 sensors
TCRT5000 ring.
IR alignment
Keep them coplanar.

Tune the MT3608 to 5.0 V

The paper uses an MT3608 step-up so the 3.7 V pack becomes a 5 V rail (motors included).

  1. PSU + → VIN+, PSU GND → VIN−. Meter on VOUT+/VOUT−.
  2. Set the bench supply to 4.0 V, current limit 0.30 A.
  3. Turn the trimpot slowly toward 5.00 V. Do not overshoot.
  4. Recheck under a short dummy load: 100 Ω (~50 mA), then 6.2 Ω (~0.8 A) or 5 Ω (~1.0 A) in bursts.
  5. Power off. Mark the module “5 V”.
MT3608 wiring
Boost module on the bench.
Measuring 5 V
Trim to 5.00 V.

Electrical checks

Unpowered: GND continuity; 0 Ω jumpers R9/R15; no 5 V↔GND or 3V3↔GND shorts.

Powered (bench or battery): 5.0 V / 0.3 A limit, switch on, watch quiescent current. Nothing should run hot.

Power-up check
First power-up.
Current-limited supply
Stay current-limited.

Drive the WS2812B with a blink or rainbow. Confirm I²C pull-ups (~4.7 kΩ to 3V3) and an MPU6050 ACK if the e-hat is fitted. Walk the CD4051 channels; IR voltages should move with a white/black card.

LED test
LED bring-up.
IR channel test
IR / mux check.

Optional smoke test: flash the stock firmware over USB (battery disconnected) and watch the serial boot at 115200.

Next: print the body