MAKER: JuanF92 / Translated by: Fun Endless, Meeting is Just the Beginning
MicroByte is a micro console capable of running games from NES, GameBoy, GameBoy Color, Game Gear, and Sega Master System, all components designed within this 78 x 17 x 40 mm package. Despite its small size, it conforms to the layout of SNES game boards and features operational buttons.
It also comes with a clear 1.3-inch IPS display, allowing you to see all the details of the games.
Subsequently, Python and Arduino libraries will be updated for development beyond gaming.
Firmware, PCB design, 3D files for the casing, etc., can be downloaded from the project repository: https://make.quwj.com/project/359
BOM List: https://github.com/jfm92/microByte_PCB/blob/main/microByte_BOM.xlsx
Project Architecture
When starting an electronic project, a block diagram is usually created first, outlining the required functions and interactions, followed by drawing the schematic. In the schematic, components that meet the requirements are selected, and electrical connections are made, followed by PCB layout design. Finally, the positions of each component base are set according to design rules and physical design guidelines.
The above is the original version based on a breadboard, and below is the final version.
This project will follow a modular approach for development, supplemented by schematic design and PCB layout design.
The schematic and PCB layout for this project are designed using Kicad, download link: https://github.com/jfm92/microByte_PCB/tree/5cb0fcf7a9658e331d677588a7f35327a7d491d7
To open it, simply install Kicad and double-click the .pro file.
ESP32 Microcontroller
First, select an appropriate microcontroller; for this project, the ESP32 Wrover E module is chosen. This module/microcontroller features: 240 MHz dual-core, 16 MB flash, 8 MB RAM, ultra-low power co-processor, supports Wi-Fi and Bluetooth, and a full set of peripherals and GPIO, providing excellent emulation performance.
Refer to Espressif for design; the datasheet is as follows: https://www.espressif.com/sites/default/files/documentation/esp32-wrover-e_esp32-wrover-ie_datasheet_en.pdf
The schematic of the board module:
In the middle is the ESP32 module connected to peripherals.
Pin 25 is the IO 0 pin. This pin is used to select the boot state of the device, allowing new firmware to be flashed or booting from already flashed firmware. A high signal boots from the flashed firmware; a low signal enters boot mode and waits for new firmware.
Pin 3 is the enable pin (also known as reset). If this pin is high, the microcontroller will operate; otherwise, it will not. To avoid signal bouncing, an RC circuit (resistor/capacitor) is included here to generate a clean signal at board startup or transitions to prevent accidental resets. While this circuit does not have a reset button, it is advisable to remain cautious.
Pin 24 is the IO 2 pin, connected to a blue LED with a resistor, serving as a notification display. Let’s take a look at pin 2 or VDD 3V3. This pin provides power to the chip at 3.3 V. Note the parallel capacitors; these are decoupling capacitors used to eliminate parasitic interference.
Below are the PCB design layout and key parts of the PCB board under study.
In addition, related components must be placed as close as possible.
Adding USB Module
The USB transceiver is a chip that converts USB signals to serial, RS232, or other similar protocols. There are various models available on the market, and here we use CH340C.
CH340C does not require an external clock like CH340G; it is easy to use and costs only a fraction of CP2102 or FT232.
As shown on the right side of the image. Its design is very simple, consisting of just one chip, with two decoupling capacitors and a 0-ohm resistor. If unsure whether a connection is necessary, use this resistor as a bridge.
On the right is a schematic of the USB-C connector. Its function is to connect to a PC and charge the battery. Using USB-C in PCB wiring is more challenging because it requires dual connections that can be used in any direction.
Tip: USB signals are parallel high-speed signals and should be routed as parallel as possible to avoid crosstalk between signals and keep signal lines close to digital logic chips.
Battery and Power Management
This section is divided into three parts: battery charging and protection circuit, power management, and battery level control. Battery charging and protection circuit:
For using Li-Po batteries, safety is paramount; a proper constant current charging controller must be made to avoid charging above 4.2 V or discharging below 2.8 V to prevent battery damage.
TP4056 is a lithium polymer battery charger chip that provides constant linear voltage current and can set the charging current by modifying the value of R2. Remember, the charging current should be around 25% of the battery capacity. This chip connects to LED D1 to indicate the charging status of the battery.
FS312F-G is a battery protection circuit chip that will cut off battery use if it detects overcharging or over-discharging. This helps to avoid battery damage.
FS8205 is a chip that integrates two MOSFET transistors to select circuit power; if the battery is within the appropriate range, it will draw energy from the battery; if the device is connected to the USB port, it will directly use USB power.
Power Management:
This module is a boost circuit for voltage conversion, providing a constant voltage of 3.3 V. The maximum charging voltage for lithium batteries is 4.2 V, and the minimum safe voltage is 2.8 V. Therefore, a constant voltage is required to avoid instability in the microcontroller or low brightness on the display. To solve this problem, MT3608 is used here, which is a configurable boost voltage converter. At the output of this circuit, the voltage is 4.2 V, higher than the required 3.3 V, so the MCP1700 voltage converter is used to convert the voltage from 4.2 V to 3.3 V.
This solution may have issues of over-design or inefficiency, but it is the cheapest effective solution.
Battery Level Control:
Similar to the voltage divider before the boost circuit. The voltage at this point will reach a maximum of 4.2 V, so only a voltage divider to reduce it to 3.3 V needs to be designed to comply with the ESP32 logic level and connect it to the ADC GPIO to measure the analog level signal.
Designing the SD Card Module
The SD card uses the SPI protocol, which is a bidirectional communication method that allows for high-speed communication. When using peripherals, there is no need to worry about crosstalk, as its speed is insufficient to generate a magnetic field (at least there are no problems here).
The circuit is also very simple; connect each line to the MCU’s SPI GPIO port and add a pull-up resistor. This resistor is important for maintaining a constant high level on the line and avoiding intermediate level signals that could damage data transmission.
Here are our old friends, the decoupling capacitors.
Audio Output
Using ESP32, there are two ways to output audio. By checking the datasheet, we can use the integrated I2S to DAC converter or directly use the I2S peripheral.
The simplest way to obtain audio output is to use the I2S to DAC converter, as speakers can be directly connected to GPIO; if the audio volume is very low, an analog audio amplifier can be used, which is very easy to implement. However, this solution also brings some inconveniences. The DAC only uses 8 bits out of the 16 bits of I2S, meaning a lot of audio information will be lost, resulting in very poor audio quality.
I2S is a digital audio protocol that guarantees high-fidelity audio without loss of quality or noise. However, a converter is needed to convert the signal received by the amplifier. Here, we use the MAX98357 audio amplifier. This amplifier converts I2S signals into analog signals and amplifies them for direct connection to speakers or headphones. This amplifier/converter provides us with 6.4W of output power and has configurable output options—selecting between mono or stereo audio and impedance.
Disclaimer: My understanding of audio is not very deep, so some audio data may be incorrect and is for reference only.
Adding Buttons
ESP32 is a great module, but it has a limited number of GPIO ports. However, there is no need to worry; we have the TCA9555 solution.
TCA9555 is an I2C GPIO multiplexer. This device allows for up to 18 additional GPIOs. These GPIOs can be used as inputs or outputs and can be controlled or checked via I2C. Therefore, using just two GPIOs (I2C SDA and I2C SCLK), you get 18 additional GPIOs! Latency is not an issue, as data can be read or written at up to 400 KHz, meaning 400,000 times per second!
Let’s take a look at the schematic. This multiplexer can be used with I2C, so each signal needs to be pulled up to avoid noise on the lines. It also has an interrupt pin, but it is not used. The I2C signals are the SCL and SDA pins (19 and 20). The device address needs to be configured through hardware by setting the logic levels of pins A0, A1, and A2. Here, there is only one I2C device, so the address is given as 0x00.
Finally, all switch buttons are directly connected to the chip, and we configured the pull-up or pull-down resistors through software since this multiplexer has configurable internal resistors.
One interesting aspect of this device is the capacitive buttons, which are PCB traces without a silkscreen layer, so rubber buttons with carbon film can be used as switch buttons. This is a common configuration on game controllers. If you want to use it in your design, you can find it in the library that comes with the project.
Pairing with a Beautiful Display
The display uses an IPS 1.3-inch screen with a resolution of 240 x 240 px, providing very nice colors and clear images. The communication protocol is SPI, allowing for a frame rate of up to 70 FPS (as noted in the datasheet). On the other hand, the backlight of the display can be controlled to select brightness levels. This is done via the BS138 MOSFET transistor, which controls the current to the embedded LED on the display.
Completion
Now you can run this retro game console and start your journey of retro gaming memories!
The code used in the project can be downloaded from the project repository: https://make.quwj.com/project/359
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