The U3A_rs485 project is based on a (THVD1452) that ist used to change the RX/TX signals to the required differential signal level of TIA/TIA-485-A standard. It can simply be adapted to the U3A-Module.
To use it with a DSUB connector it is necessary to solder a connection cable to the DSUB that can be connected with the screw terminal.
| Experience | Level |
|---|---|
| Soldering | |
| Mechanical |
| Type | File | Description |
|---|---|---|
| Schematic | pdf / cadlab | Schematic files |
| Board | pdf / cadlab | Board file |
| Drill | Drill file | |
| BoM | xlsx / html | Bill of Material as Excel/interactive HTML |
| PCB | zip / tar | KiCAD/Gerber/BoM/Drill files |
| Mechanical | zip / tar | FreeCAD/Housing and PCB (STEP/STL) files |
There are two parts of the hardware. The pcb and the housing of the U3A_rs485. The pcb is created with KiCAD and the housing with FreeCAD. All files are built with github actions so that they are ready for a production environment. The housing is printed with a 3D-printer (Dremel 3D40).
The circuit board is populated on both sides (Top, Bottom). The best way for soldering the SMD components is within a vapor phase soldering system and for the THT components with a standard soldering system.
The housing has a tolerance of 0.2mm on each side of the case. So the pcb should fit perfectly in the housing. The tolerance can be modified with FreeCAD in the Parameter Spreadsheet.
The U3A_rs485 is powerd over the U3A board with 5V. The voltage of the pins are driven by a THVD1452 for data transmission that meets the TIA/TIA-485-A standard.
#
# +-----------------------------------+ +-----------------------------------+ +---------------------+
# | J2| |J2 U +---+---+ | |
# | J1 U3A_rs485 +--+--+ +--+--+ S U | USB |--+ +-----------------+ |
# +--+--+ | VCC +-----+ VCC | B UPDI 3 +---+---+ | | TeraTerm | |
# + VCC | T +---+ | GND +-----+ GND | / +---+---+ A | | | ~~~~~~~~ | |
# +-----+ E | X | J | X +-----| PDI | U | | | | | | ~~~~~ | |
# L +---+ A | R | X | 3 | CTS +-----+ CTS | A | | | | | | ~~~~~~~~~~~~ | |
# O | +-+ B | M +---+ | RTS +-----+ RTS | R | X | X | | | | | |
# O +-|-+ Y | ~ . | X | J | TXD +-----+ TXD | T +---+---+ +-+ | | +-----------------+ |
# P +-+ Z | P T 1 | X | 5 | RXD +-----+ RXD | / / / | | |
# B +-----+ W X 2 +---+ +--+--+ +--+--+ U +-+-+-+-+-+-+ | Computer |
# A + GND | R D 0 | | P | 5V | 3V3 | | |
# C +--+--+ E E Ω | | D +-----+-----+ +---------------------+
# K | N N | | I J4 |
# | +---+---+---+---+---+---+---+---+ | | +---+---+---+---+---+---+---+---+ |
# | | V | C | C | D | D | D | R | G | | | | V | C | C | D | D | D | R | G | |
# +-+ C | B | B | C | T | C | I | N +-+ +-+ C | B | B | C | T | C | I | N +-+
# | C | 3 | 2 | D | R | R | | D | | C | 3 | 2 | D | R | R | | D |
# +---+-+-+-+-+---+---+---+---+---+ +---+-+-+-+-+---+---+---+---+---+
# | | | |
# | +-------------------------------------------|---+
# +-----------------------------------------------+| Type | Link | Description |
|---|---|---|
| THVD1452 | UART / RS485 level converter | |
| KiCAD | web | KiCAD project page |
| FreeCAD | web | FreeCAD project page |
R. GAECHTER