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01
MicroByte is a micro console that can run games from NES, GameBoy, GameBoy Color, Game Gear, and Sega Master System, all designed within a 78 x 17 x 40 mm package.
Despite its small size, it conforms to the layout of an SNES game board and has operational buttons.
Additionally, it features a clear 1.3-inch IPS display that allows you to see all the game details.
Subsequently, Python and Arduino libraries will be updated for development beyond gaming.
Firmware, PCB design, and 3D case files 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
02
When starting an electronic project, the first step is usually to create a block diagram that sets the required functions and interactions for the project, followed by drawing the schematic. On the schematic, select components that meet the requirements and make electrical connections, then proceed to PCB layout design.
Finally, set the position of each component base 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 be developed following a modular approach, supplemented with schematic design and PCB layout design.
The project schematic and PCB layout were 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.
03
First, select an appropriate microcontroller; for this project, the ESP32 Wrover E module is chosen.
Features of this module/microcontroller: 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, with excellent emulation performance.
For design references, consult Espressif, datasheet available here: https://www.espressif.com/sites/default/files/documentation/esp32-wrover-e_esp32-wrover-ie_datasheet_en.pdf
Here is the schematic of the circuit board module:
In the middle is the ESP32 module connected to peripherals.
Pin 25 is the IO 0 pin. This pin is used for selecting the boot state of the device; it can flash new firmware or boot the already flashed firmware. A high signal starts 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 work; otherwise, it won’t. To avoid signal bouncing, there is an RC circuit (resistor/capacitor) here to produce a clean signal during board startup or transitions to prevent accidental resets. While this circuit does not have a reset button, it is best to err on the side of caution.
Pin 24 is the IO 2 pin, connected to a blue LED with a resistor, serving as a notification display.
Let’s look at pin 2 or VDD 3V3. This pin powers the chip, with a voltage of 3.3 V. Note the parallel capacitors; these capacitors are decoupling capacitors used to eliminate parasitic interference.
Below is the PCB design layout and key areas of focus within the PCB board.
Additionally, related components must be as close as possible.
04
The USB transceiver is a chip that converts USB signals to serial, RS232, or other similar protocols. There are various models available in the market; here we use CH340C.
CH340C does not require an external clock like CH340G, is easy to use, and is priced at a fraction of CP2102 or FT232.
As shown on the right side of the diagram. Its design is very simple, consisting of only one chip with two decoupling capacitors and a 0-ohm resistor. If unsure whether a connection is necessary, use this resistor as a jumper.
On the right is a schematic of the USB-C connector. Its purpose is to connect to a PC and charge the battery. Using USB-C makes PCB wiring more challenging, as dual connections need to be added to allow wires to be used in any direction.
Tip: USB signals are parallel high-speed signals, and wiring should be as parallel as possible to avoid crosstalk between signals, and signal lines should be routed close to digital logic chips.
05
This section is divided into three parts: battery charging and protection circuit, power management, and battery level control.
Battery charging and protection circuit:
For the use of Li-Po batteries, safety comes first. A proper constant current charging controller needs to be made to prevent charging above 4.2 V or discharging below 2.8 V to avoid damaging the battery.
TP4056 is a lithium polymer battery charger chip that provides a constant linear voltage current and can set the charging current by modifying the resistance of R2. Remember that the charging current should be around 25% of the battery capacity. This chip connects to LED D1 to indicate the battery’s charging status.
FS312F-G is a battery protection circuit chip that cuts off battery usage if overcharging or excessive discharging is detected. This prevents battery damage.
FS8205 is a chip that integrates two MOSFET transistors to select circuit power. If the battery is within an appropriate range, it will draw energy from the battery; if the device is connected to the USB port, it will work directly using USB power.
Power management:
This module is a boost circuit of the voltage converter that provides 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 issue, MT3608 is used here, which is a configurable boost voltage converter. At the output of this circuit, the voltage is 4.2 V, above 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 with over-design or inefficiency, but it is the cheapest effective solution.
Battery level control:
Just like 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 needs to be designed to reduce it to 3.3 V to comply with the ESP32 logic level and connect it to the ADC GPIO to measure the analog level signal.
06
SD cards use 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 not sufficient to generate a magnetic field (at least there are no issues 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 crucial for maintaining a constant high level on the line and avoiding intermediate level signals that could disrupt data transmission.
Here we also have our old friends, the decoupling capacitors.
07
With the 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 low, an analog audio amplifier can be used, which is very easy to implement. However, this solution also has 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 poor audio quality.
I2S is a digital audio protocol that guarantees high-fidelity audio without quality loss or noise. However, it requires a converter to process the signals received by the analog converter and amplifier. Here we use the MAX98357 audio amplifier.
This amplifier converts the I2S signal to an analog signal and amplifies it for direct use with speakers or headphones.
This amplifier/converter can provide us with 6.4W of output power and has configurable output options—selecting between mono or stereo audio and impedance selection.
Disclaimer: My understanding of audio is not very deep, so some audio data may be incorrect and is for reference only.
08
The ESP32 is a great module, but it has a limited number of GPIO ports. However, don’t 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.
Thus, using only two GPIOs (I2C SDA and I2C SCLK), we have 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.
I2C signals are on the SCL and SDA pins (19 and 20). The device’s address needs to be configured through hardware by setting the logic levels of pins A0, A1, and A2. Since there is only one I2C device here, the address is given as 0x00.
Finally, all switch buttons are directly connected to the chip, and we set the pull-up or pull-down resistors through software configuration, as this multiplexer has configurable internal resistors.
One interesting feature of this device is the capacitive buttons, which are PCB traces without silk-screen layers, allowing rubber buttons with carbon film to act as switch buttons. This is the usual configuration on game controllers. If you want to use it in your design, you can find it in the library that accompanies the project.
09
The display features a 1.3-inch IPS 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 by controlling the current of the LED embedded in the display via a BS138 MOSFET transistor.
Completion
You can now run this retro game console and start your journey of retro gaming memories!
The code used in this project can be downloaded from the project repository: https://make.quwj.com/project/359
Disclaimer:
