2 layers99.3 × 98.6 mm
FlexiblePS
profdc9/FlexibleCharger
An Arduino-controlled charger for different kinds of batteries, or it can be a standalone power supply
118 parts13
2 layers
PCB Etching Unit
UNIT-MOS/PCB-Etching-UnitThe board etching unit (BEU) aids in the etching of PCB's with ferric chloride (Fe3Cl).
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 92
- Nets
- 98
- Pads
- 337
- Tracks, vias
- 215, 4
- Pours
- 2
- Routed
- Yes
- KiCad
- KiCad 9.0 (file 20241229)
- Created
- 22 Dec 2025
- Updated
- 26 Dec 2025
Overview
PCB Etching Unit is an open-source printed circuit board by UNIT-MOS, from the UNIT-MOS/PCB-Etching-Unit repository on GitHub. It is a 2-layer board with 92 parts on 98 nets, routed with 215 tracks and 4 vias.
It is built around the HDSP-7801, TIP42 and BC558, with the TIP41 among its other parts. Its parts include 40 resistors, 20 transistors, 9 diodes, 8 ICs and 7 switches. It belongs with the AVR (ATmega, ATtiny) boards of this library.
Main components
4
HDSP-7801
插件0.3 1 105mW 12.7mmx7.62mmx6.09mm 7 Segment Common Anode Green 插件 LED Segment Displays ROHSBroadcom LimitedLED Segment Displays
TIP42
TO-220-32W 30 3MHz 40V 6A 700uA PNP TO-220-3 Bipolar (BJT) ROHSonsemiBipolar (BJT)
BC558
TO-921 PNP 100mA 100nA 150MHz 30V 500mW 5V 800 90mV、250mV PNP TO-92 Bipolar (BJT) ROHSDDFBipolar (BJT)TIP41
TO-220TO-220 Bipolar (BJT) ROHSTFBipolar Transistors - BJT
README
README.mdBoard Etching Unit (BEU)
The BEU assists in the etching of PCB'S using FeCl3, so the operator gets to do more interesting things in the meantime. BEU aims to achieve the following goals
- material cost below 50€
- moving FeCl3 container
- FeCl3 heater
- open loop
- closed loop control using thermoelement
- timer
- speed control
Revision 0
- material cost below 50€
- moving FeCl3 container
- FeCl3 heater
- open loop
- closed loop control using thermoelement
- timer
- speed control
Assembly
Two DC motors will move the FeCl3 container directly by connecting to drilled holes.
A 3D-printed support beam will hold the motors at a sufficient height.
Desired dimensions can be configured in the OpenScad-file.
This should enable the operator to choose a container of arbitrary width or length. If a chosen container
is small enough to be held by one motor, a single support beam with a counterweight can be used.
PCB
In the spirit of this project, the board will be etched by the operator.
The operator can read up on the procedure here, it's the best primer for selfmade PCB's we've found so far.
Comments
Used my dormant Arduino Uno board for revision 0. A dev board for 20€ is fine for revision 0 but it did screw over the goal of low material cost.
Following revisions might use a PIC, the instruction set seems compact enough for some assembly and I found several primers covering them (IDE: PIKDEV).
Though the AVR software will be done in C for now.
Since I'm using a plastic container, I skipped on heating the FeCl3 this time. Aluminium seems to be easy to solder/weld, might be used for later revisions.
Closed loop temperature controll could be done using a PT100 or Typ K element, if the casing survives extended exposure to FeCl3.
The board just etches on one side, with the other one facing down. A support beam could hold it up, but the support itself would cover parts of the board too.
Vertical support on the left and right with 1 mm width could work.
Parts
92| Qty | Value | Footprint | References |
|---|---|---|---|
| 21 | 1K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R1, R2, R10, R12, R13, R16, R18, R19, R20, R21, R23, R25, R26, R30, R32, R34 +5 |
| 8 | 1N4001 | Diode_THT:D_DO-41_SOD81_P10.16mm_Horizontal | D1, D2, D3, D4, D5, D6, D7, D8 |
| 8 | TIP42 | Package_TO_SOT_THT:TO-220-3_Vertical | Q1, Q2, Q3, Q4, Q5, Q8, Q10, Q13 |
| 7 | 2.2K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R3, R6, R8, R11, R31, R33, R35 |
| 7 | BC558 | Package_TO_SOT_THT:TO-92_Inline | Q14, Q15, Q16, Q17, Q18, Q19, Q20 |
| 7 | SW_MEC_5G | Button_Switch_THT:SW_TH_Tactile_Omron_B3F-106x | SW1, SW2, SW3, SW4, SW5, SW6, SW7 |
| 4 | 5.6K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R15, R17, R22, R24 |
| 4 | HDSP-7801 | Display_7Segment:HDSP-7801 | U1, U2, U3, U4 |
| 4 | TIP41 | Package_TO_SOT_THT:TO-220-3_Vertical | Q6, Q7, Q9, Q11 |
| 3 | 100nF | Capacitor_THT:C_Disc_D9.0mm_W5.0mm_P5.00mm | C1, C2, C3 |
| 2 | 330R | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R28, R40 |
| 2 | 4027 | Package_DIP:DIP-16_W7.62mm | U5, U6 |
| 2 | Motor_DC | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | M1, M2 |
| 1 | 15K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R38 |
| 1 | 2K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R27 |
| 1 | 2N3904 | Package_TO_SOT_THT:TO-92_Inline | Q12 |
| 1 | 3.3K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R14 |
| 1 | 4011 | Package_DIP:DIP-14_W7.62mm | U9 |
| 1 | 4511 | Package_DIP:DIP-16_W7.62mm | U11 |
| 1 | 470K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R39 |
| 1 | 5K | Potentiometer_THT:Potentiometer_Piher_T-16H_Single_Horizontal | RV1 |
| 1 | 6.8K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R37 |
| 1 | 620R | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R29 |
| 1 | Arduino_UNO_R2 | Module:Arduino_UNO_R2_WithMountingHoles | A1 |
| 1 | Buzzer | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | BZ1 |
| 1 | LED | LED_THT:LED_D3.0mm | D9 |
Questions
What parts does the PCB Etching Unit use?
92 parts, built around the HDSP-7801, TIP42, BC558 and TIP41. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the PCB Etching Unit KiCad files?
From the UNIT-MOS/PCB-Etching-Unit repository on GitHub, at the commit this page was made from: the board is PCB_Etching_Unit/PCB_Etching_Unit.kicad_pcb and its schematic PCB_Etching_Unit/PCB_Etching_Unit.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the PCB Etching Unit design in my own project?
Its repository states no licence, so its author keeps all rights: ask UNIT-MOS before reusing the design.
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