The project debuted on the Chinese version of the forum [OSHWHub](https://oshwhub.com/yangzen/zui-gai68-)
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In Chinese, this name is described as bargain among bargain goods, which means very bargain.
Place a common SCM configuration comparison table with QMK scheme
| MCU model | STM32F103C8T6 | GD32F103C8T6 | ATMEGA32U4-AU | CH551G |
| --------- | ------------- | ------------ | ------------- | ------ |
| lcsc code | C8734 | C77994 | C44854 | C108958 |
| unit price（2022/6/24） | US$ 7.6784 | US$ 2.5877 | US$ 23.4282 | US$0.4851 |
| encapsulation | LQFP-48 | LQFP-48 | QFP-44 | SOP-16 |
| I/Os | 37 | 37 | 26 | 12.5(RST feet can only be read when half) |
| bits wide | 32-Bit | 32-Bit | 8-Bit | 8-Bit |
| core | ARM® Cortex®-M3 | ARM® Cortex®-M3 | AVR | C51 |
| ROM | 64kB | 64kB | 32kB | 10kB |
| RAM | 20kB | 20kB | 2.5kB | 0.75kB |
| EEPROM | None (but can be simulated in FLASH) | None (but can be simulated in FLASH) | 1kB | 128B |
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If you make a copy of your work, for example by selling it on eBay and making a profit, please pay $0.50 per copy as a commercial license fee.
Due to the inconvenient payment method, if you are not in China and want to award this project or pay the authorization fee, please enter the Sponsorship of openRGB and take a screenshot in the comments section. Thank you. Taiwan compatriots please send money to me.
### 1.function Introduction
Press the FN
### 2.Hardware Introduction
This is the circuit of the mechanical keyboard on the market (QMK's scheme is such), a typical matrix keyboard with anti-keystroke diodes.
This is my new matrix keyboard scanning circuit
If you analyze the circuit with ideal diodes, you will get confused,
while pressing S1,S3.
Uio2=Uio3=0V when scanning IO1 bit low?
This will read S1,S2 press???
This is the voltammetric characteristic diagram of onsemi 1N4148, and note that the horizontal axis is exponential.
It can be seen that there is a positive guide voltage drop of 500mV even at the lowest current of 0.1mA.
Combined with the above questions, it can be inferred that Uio2=0.5V and Uio3=1V.
At this time, we will check the MCU electrical parameters
![屏幕截图 2022-06-12 162819.png](//image.easyeda.com/pullimage/K8ORZKtVLKwvNXcDjohwgaDAu1NfNJ4JzJ1SFDfJ.png)
This is the technical document of CH552G. It is clear which supply voltage to choose.
Then through the real machine test, it is necessary to add the pull-up resistance to increase the diode conduction current and increase the voltage drop to obtain a more stable scanning detection effect.
### 3.Assembly note
The bottom plate is fixed with solder welded copper nut
Some holes need to plug screws in advance, and then weld switches
### 4.Write the firmware
If the software is opened in Chinese, please turn on this setting to switch to English mode
To burn the firmware, perform the following operations. Before the fifth step, press BOOT to insert the USB and release BOOT
## Firmware update content
1. Improve USB code
2. When the indicator is turned off, the CapsLock turns on a white indicator
1. Add SD card reading light effect. When detecting flicker, space will blink. Function off by default, 5 consecutive light effect control to switch, power off save
Change a batch