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Hardware.md

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FNIRSI-5012H Hardware

There are two models of the PCB. The first revision has 4 mechanical relays. The second revision has only one mechanical relay. The text below only applies to the second revision.

Main components on the board

  • GD32F407VET6 - MCU (Cortex-M4, 512 KB Flash, 192 KB SRAM)
  • AD9288 (most likely a clone, no markings) - ADC
  • TP4056 - Li-lon Battery Charger
  • TLV70033DDCR - 3.3 V LDO
  • PC817 - Photocoupler
  • CPC1002N - Optically coupled solid state relay
  • SN74HC148 - 8-line to 3-line priority encoder
  • SS8550 - PNP transistor
  • HFD4 - Mechanical relay
  • OPA356 - 200 MHz, CMOS OpAmp
  • W25Q64JV - 64 Mbit SPI Flash
  • TFT Display - Based on ST7789S

ADC

The ADC is pin-compatible with AD9288, but there are a couple of pins in the original that are marked NC, but bypassed to ground with capacitors in this design. It also has a hemispherical dimple for the first pin marker. The original has a flat bottom dimple. So it is most likely a clone, but fully pin-compatible. It might be MXT2088.

Power System

There are two LDOs in the system. One is the main LDO powering all the components. The other one is dedicated to the LCD backlight. The brightness is controlled by PWMing the enable signal.

The LDO inputs are always supplied by the battery and he power switch controls enable pin of the main LDO.

USB

The USB connector has programming pins (SWDIO/SWCLK) on the data pins, so this connector is used for initial programming during the manufacturing process.

As a result there is no way to get USB working without hardware modification. Modification would be relatively easy to do. USB FS data pins are located right next to the programming pins. But I'm not sure there is any value to having USB on this device.

Buttons

SN74HC148 are used to read the keyboard. Each IC handles 8 buttons and two buttons are connected directly to the MCU pins (for a total of 18 buttons).

Allocation of keys to priority encoders (PE):

Channel PE0 PE1
0 STOP 50%
1 F1 TRIG DOWN
2 EDGE TRIG UP
3 AC/DC TRIG
4 UP MENU
5 RIGHT SAVE
6 MODE LEFT
7 AUTO DOWN

F2 and 1X10X are connected directly to the MCU pins.

It is an interesting way to reduce the number of pins required for the keyboard, but obviously only one key from the group can be detected at a time, even if multiple keys are pressed.

Other Hardware

  • CPC1002N is used for shorting the AC/DC capacitor.
  • SS8550 are used to control PC817s and a mechanical relay.
  • OPA356 is a buffer right before the ADC.
  • W25Q64JV is used for waveform storage (and possibly settings, but not the firmware).

Attenuation (Vertical Scale Control)

Attenuation is set though the 7 transistors (controlling optocouplers and a relay). I number the transistors Q0-Q6 starting from the one closest to the BNC connector. Each volts/div setting enables one transistor:

  • 10 V/div - Q4
  • 5 V/div - Q5
  • 2 V/div - Q6
  • 1 V/div - Q1
  • 500 mV/div - Q0
  • 200 mV/div - Q2
  • 100 mV/div and 50 mV/div - Q3

50 and 100 mV/div are not different on the hardware level, so the amplitude is just changed in the software. This is also the only range that is controlled using a mechanical relay.

Front-end

Here is a schematic of the front-end of this oscilloscope. None of the capacitor values are known.

Transistors are part of the optocouplers. The paired transistors are the same optocouplers, but they are driven at the same time (LEDs on the other side are in series).

FNIRSI-5012H Front-end

GD32F407VET6 Pinout

And finally, the full pinout of the MCU.

ADC

Pin Function
PD0  ADC B D0
PD1  ADC B D1
PD2  ADC B D2
PD3  ADC B D3
PD4  ADC B D4
PD5  ADC B D5
PD6  ADC B D6
PD7  ADC B D7
PD8  ADC A D7
PD9  ADC A D6
PD10 ADC A D5
PD11 ADC A D4
PD12 ADC A D3
PD13 ADC A D2
PD14 ADC A D1
PD15 ADC A D0
PA8  ADC A CLK
PA9  ADC B CLK

LCD

Pin Function
PC6  LCD_RESET
PB3  LCD_RD
PB4  LCD_WR
PB5  LCD_RS
PB6  LCD_CS
PE0  LCD_D0
PE1  LCD_D1
PE2  LCD_D2
PE3  LCD_D3
PE4  LCD_D4
PE5  LCD_D5
PE6  LCD_D6
PE7  LCD_D7
PB0  LCD_BL_EN

Vertical Controls

Pin Function
PB9  Q0
PB8  Q1
PB7  Q2
PC12 Q3
PC11 Q4
PC10 Q5
PA15 Q6
PC15 AC/DC
PA4  Offset (DAC output)

Keyboard

Pin Function
PE13 PE0.A0
PB14 PE0.A1
PB13 PE0.A2
PE14 PE0.GS
PE15 PE1.A0
PB12 PE1.A1
PB11 PE1.A2
PB10 PE1.GS
PE12 BTN_1X10X
PE11 BTN_F2

Flash

Pin Function
PA3  FLASH_CS
PA5  FLASH_CLK
PA6  FLASH_MISO
PA7  FLASH_MOSI

Miscellaneous

Pin Function
PB15 CHARGE
PB1  VBAT_SENSE (Vbat / 2)
PHx 20 MHz Crystal
PA13 SWDIO
PA14 SWCLK