Electrical characteristics
Battery
Chromapi is powered by two 18650 Li-ion cells, housed in a holder inside its body.
| Property | Value |
|---|---|
| Cells | 2 Molicel INR18650-P28A |
| Configuration | 2S (series) |
| Nominal voltage | 7.2V |
| Voltage range | 6.0V - 8.4V |
| Capacity | 2800 mAh |
| Energy | ≈ 20 Wh |
| Max. discharge current (per cell) | 35 A |
Warning
Li-ion cells can be dangerous in case of short circuit, impact or deep discharge. Use brand-name cells, and never leave the robot charging unattended.
Charging and protection
Chromapi has a USB-C charging port, directly on the motherboard. The board also includes a protection circuit against over-discharge, over-current and short circuits (BMS), to preserve the batteries and limit risks.
| Property | Value |
|---|---|
| Battery life | h |
| Charging time | h |
Power monitoring
The robot’s power consumption is continuously measured by an INA226, placed right after the power switch.
| Property | Value |
|---|---|
| Component | INA226 |
| Measured quantities | Voltage, current and power |
| Shunt resistor | 2 mΩ |
| Max. measurable current | 8 A |
| Interface | I2C at 400 kHz (address 0x40) |
| Reading rate | 10 Hz |
The current voltage running through Chromapi is constantly displayed by a status LED on the motherboard.
Regulation and distribution
| Rail | Regulator | Type | Loads |
|---|---|---|---|
| V_SYS (6.0 - 8.4V) | — | Battery voltage, after protection and monitoring | Servomotors |
| +5V | TPS51388 | Switching regulator (Buck), 600 kHz | Raspberry Pi, fan, RGB LED ring |
| +3.3V | LD39050 | Linear regulator (LDO), powered by the +5V rail | STM32 MCU, IMU, power monitor, audio amplifier and microphone |
Power architecture
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flowchart TD
CHG[["USB-C charge<br/>CN3302"]] -.->|"charge → B+ ≈ 7.2–8.4V"| CELLS[("Battery<br/>18650 x2")]
CELLS -->|"B+/BM/B-"| HY["HY2120<br/>BMS protection"]
HY -->|"B+"| SW[["Power switch"]]
SW -->|"V_BATT ≈ 7.2–8.4V"| SHUNT[["INA226 shunt sense<br/>2mΩ"]]
SHUNT -->|"V_SYS ≈ 7.2–8.4V"| REG5{{"Voltage regulation<br/>TPS51388 · Fsw=600kHz"}}
SHUNT -->|"V_SYS"| SERVOS(["Servomotors x12<br/>Feetech STS3215-C001"])
REG5 -->|"+5V"| RPI["Raspberry Pi"]
REG5 -->|"+5V"| FANPWR(["Fan<br/>Noctua NF-A4x10"])
REG5 -->|"+5V"| LEDPWR(["RGB LEDs<br/>WS2812B"])
REG5 -->|"+5V"| REG33{{"Voltage regulation<br/>LD39050 LDO"}}
REG33 -->|"+3.3V"| MCU["MCU<br/>STM32G431KBT6"]
REG33 -->|"+3.3V"| IMU["IMU<br/>BMI088"]
REG33 -->|"+3.3V"| INA["Power monitor<br/>INA226"]
REG33 -->|"+3.3V"| AUDIO["Speaker + Microphone<br/>MAX98357A / ICS-43434"]
classDef power fill:#dd2757,color:#ffffff,stroke:none
classDef voltreg fill:#ea684c,color:#ffffff,stroke:none
classDef ic fill:#25b3ae,color:#ffffff,stroke:none
classDef actuator fill:#c027e7,color:#ffffff,stroke:none
classDef sensor fill:#5c5aed,color:#ffffff,stroke:none
class CHG,CELLS,HY,SW power
class REG5,REG33 voltreg
class MCU,RPI,AUDIO ic
class SERVOS,FANPWR,LEDPWR actuator
class SHUNT,IMU,INA sensor
Resources
- Schematics (PDF):
hardware/schematic_pdf - Manufacturing files (Gerbers, BOM, CPL):
hardware/production - Motherboard components: PCB Bill of Materials