CodeCell: Circuit Deep-Dive!

Despite its small footprint, just 1.85 cm wide, CodeCell incorporates a range of features that make it a powerful tool for various applications.

Let's break down its hardware and explore the technical specifics that your next project can benefit from.

The ESP32C3 Module

At the heart of the CodeCell is the ESP32C3 module, a compact microcontroller known for being maker-friendly in the IoT space. It combines an Arduino-compatible architecture with built-in Wi-Fi and Bluetooth Low Energy (BLE) capabilities. This integration offers the most popular connectivity options while maintaining a small form factor.

The ESP32C3 module's PCB antenna is positioned on one side, away from other components, to minimize interference and improve signal transmission and reception. This placement helps reduce the impact of ground planes or other conductive surfaces that could degrade antenna performance. The components on the bottom side are kept within the recommended clearance for the antenna. From testing we found that the antenna's performance remains unaffected by the minimal interference from a USB-C cable, as these cables are typically shielded.

The ESP32-C3 provides plenty of memory, with 4 MB of Flash and 400 KB of SRAM, making it capable of running most typical applications. Its 32-bit RISC-V single-core processor, running at up to 160 MHz, efficiently handles various tasks. This combination of memory and processing power makes the ESP32-C3 suitable for a wide range of uses.

The ESP32C3 module also supports a USB Serial/JTAG Controller, allowing us to make the CodeCell reflashable through the USB-C port and to send serial data for communication and debugging.

Power Management

The CodeCell offers flexibility in power supply options. It can be powered through the LiPo battery connector, a USB-C cable, or both.

The LiPo battery connector makes it easier than ever to safely connect the battery without the need for soldering or risking accidental shorting it.

The USB-C port serves dual purposes: it is used for both powering the device and/or reprogramming it. This multi-power option is enabled through the BQ24232 battery management chip, which features dynamic power-path management (DPPM) that can power the system while simultaneously and independently charging the battery. The battery charging process is managed in three phases: conditioning precharge, constant current, and constant voltage. To protect the battery the output voltage (Vo) is regulated though the BQ24232 chip. This output supports a maximum output current of 1500mA when powered by the LiPo battery and 450mA when powered via USB.

By default, the LiPo battery charge current is set to 90mA, ensuring a balanced and a safe charge rate for the optional 170mAh LiPo battery. Further more, for those who wish to adjust the charging rate, 0402 resistor R12 have to be de-soldered and replace it with a new resistor based on the formula (R = 870/Ichrg). This is only recommended for soldering pros, who aren’t afraid of wrestling with tiny 0402 components! Check the BQ24232 datasheet for more information on the battery charging.

The CodeCell library can provides visual feedback on the battery/usb power status via the onboard addressable RGB LED:

Low Battery Warning: When the battery voltage drops below 3.3V, the LED blinks red ten times and the device enters Sleep Mode. This helps conserve power until the device is reconnected to a USB charger.
Charging Process: During charging, the CodeCell suspends application processes, lights the LED blue, and waits for the battery to reach full charge. Once fully charged, the LED performs a breathing-light animation, indicating proximity distance detected by the sensors.
Battery Powered: When the USBC is disconnected and running from the battery power the CodeCell will light green again performing a breathing-light animation, indicating proximity distance detected by the sensors.

The power regulation is further supported by multiple decoupling capacitors, including up to two bulk capacitors of 100µF each, placed next to the battery connector. These capacitors are connected to the 3.3V and the output Vo pins to ensure stable power delivery. Additionally, the board features two TVS diodes for protection; one safeguards the USB input 5V voltage (Vin), and the other protects the output voltage (Vo). These TVS diodes provide protection against electrostatic discharges (ESD), capable of safely absorbing repetitive ESD strikes above the maximum level specified in the IEC 61000-4-2 international standard without performance degradation.

The board also includes an onboard 3.3V Low Dropout (LDO) regulator, which provides a stable power supply to its low-voltage components. This tiny NCP177 LDO chip can output up to 500mA output current with a typically low dropout voltage of 200mV at 500mA.

GPIO and Power Pins

Given the compact design, the main challenge was to maximize the use of GPIO pins. We tackled this by dividing each of the three available sides of the CodeCell into different I/O sections based on their applications. We also placed power pins along the edges of the module for easy connection to various power sources, allowing you to connect other modules, sensors, and actuators to different sides.

The bottom side has 3 pins out of 5 used for power: a ground pin (GD), a 3.3V logic-level power pin (3V3) and an optional 5V input charge pin (5V0). This 5V0 pin is connected to the USB input-voltage. This means you can use it to get 5V power when the USB is connected, or you can use it as a power input for charging instead of using the USB.. This side also contains the I2C SDA & SCL pins for adding external digital sensors. If your not using any external and the light/motion sensors, these I2C pins can be set up as GPIOs.

The other two sides each have a ground pin (GD) and a voltage output pin (VO). Each side also features 3 programmable GPIO pins (IO1, IO2, IO3, IO5, IO6, IO7), which can all be configured as PWM pins (ideal for directly connecting an h-bridge for actuator/motor control). IO1, IO2, and IO3 can also be used as ADC pins.

Sensing Capabilities

The CodeCell's standout features include its onboard sensors. Each unit comes equipped with a built-in light sensor, and there's also an optional motion sensor available to elevate your project's motion detection—especially useful for robotics and wearables!

VCNL4040 Light Sensor: This sensor measures both light levels and proximity up to 20 cm. It features a 16-bit high-resolution design that combines a proximity sensor, an ambient light sensor, and a high-power IRED into a compact package. By integrating photodiodes, amplifiers, and an analog-to-digital converter onto a single chip, it provides enhanced functionality. The I2C configuration is directly embedded in the CodeCell library, ensuring the sensor is automatically initialized to optimize its sensing resolution.
Optional 9-axis BNO085 Motion Sensor: This advanced IMU sensor is a pricey upgrade, but we believe it's well worth the investment! It upgrades the CodeCell’s capabilities with an integrated 3-axis accelerometer, 3-axis gyroscope, and 3-axis magnetometer + the BNO085’s advanced sensor fusion algorithms combines the data from these sensors to accurately determine the motion data of the sensor, like: Angular Rotational Reading (Roll, Pitch, Yaw), Motion State (e.g., On Table, Stationary, Motion), Motion Activity (e.g., Driving, Walking, Running), Accelerometer Readings, Gyro Reading, Magnetometer Reading, Gravity Reading, Linear Acceleration Reading, Tap detection, Step Counter. Both the sensor configuration and the reading of the data can easily read through the CodeCell library - Click on this guide to see how to get started.