The Central Unit of the Home Automation System consists of two carefully designed PCB-s. There are two ribbon cables which provide the communication between the boards. Each PCB is designed to perfectly fit into the Bopla Alu-Topline aluminum enclosure.
The supply board is responsible for establishing various stabilized DC voltages required by the Main board. The Central Unit can be supplied from 230V AC. The input 230V AC is filtered with a FIL5001 PCB mount filter, then the two 2x115V 3VA performance transformers establish 30V AC and 9V AC voltages. Then the AC voltages are converted to DC with Graetz-bridges. The final stabilized output voltages are 30V, 5V and 3V3 DC, which are provided with an LM2576HV (high-voltage input), an LM2576 and an LM2596 step-down converter respectively.
The Supply Board is carefully designed to avoid electric shock. 230V AC routes are present only on the bottom layer and the high-voltage areas are separated with 2mm wide milling holes to prevent high-voltage current drift on the surface of the PCB. Moreover a PMMA (Polymethyl methacrylate) plastic layer is fitted onto the bottom side of the Supply board.
Additionally, a 12V DC auxiliary input is available for development on the Supply Board. Thus the Central Unit can be supplied from a laboratory power supply to avoid using 230V AC during development.
- Two 100mA fuses
- FIL5001 230V AC filter
- DPDT switch
- Two 2x115V 3VA transformers
- B380C2200 and B380C3300 Graetz bridges
- Two LM2576 (adjustable) step-down converters
- A LM2596 (adjustable) step-down converter
- IEC 60320 C14 inlet for 230V AC input
- Mini-XLR (5-pin) connector for 12V DC auxiliary input (for development purposes)
- Mini-XLR (4-pin) connectors for RS-485 and KNX buses
The main board features the ARM Cortex-M4 core microcontroller, the graphical processor, an 5" resistive LCD touch screen, communication interfaces, plugs & connectors, LEDs, and a piezo.
- STM32F407VG ARM Cortex-M4 core microcontroller with 168MHz core clock frequency
- FTDI FT800 EVE controller
- 5" resistive LCD touch screen with MIC2289 backlight controller
- RFM73P 2.4GHz Radio module
- BTM511 Bluetooth module
- MAX3485CSA RS-485 interface module
- E981-03 KNX module
- DP83848CVV Ethernet controller
- PT-3110W Piezo with TC4425A MOSFET driver
- Six programmable LEDs
- PulseJack RJ-45 connector
- USB (Standard B) connector
- MicroSD card slot
There are 3 small PCBs which are milled out of the Main board to cut manufacturing costs. Two of them - on which there are the Bluetooth and the 2.4GHz radio module - are fitted vertically at the left and right sides of the Main board. The side panels of the enclosure is made of plastic, therefore these are the most advantageous spots to place the wireless modules and antennas. On the third small PCB, there are the microSD slot, the RJ-45 and USB connectors. This auxiliary PCB is mounted on the top-center of the main board to make the connectors and slots fit to the back of the enclosure, therefore the user can plug the cables and place the microSD card into the slot easily.
The LEDs and the LCD touch screen are mounted on the bottom side of the Main board, because the board is fitted into the enclosure upside down.
I used P-CAD for schematic and PCB layout design. I soldered all the components by hand with a Weller WS-80 soldering station. Most components were soldered with Stannol Kristall 505 0.5mm solder wire and I used Ersa F-SW 32 fluxpaste at the critical components. For hardware development and debugging, I used laboratory power supply, digital oscilloscope and multimeters. The supply board has an auxiliary input, therefore the whole Central Unit could be supplied from 12V DC to avoid electric shock during development.
From the beginning, the Central Unit was designed to perfectly fit into a nice and ergonomic Bopla Alu-Topline aluminum enclosure. The top part of the enclosure is tilted, thus the higher thru-hole components (eg. transformers, electrolytic capacitors) can fit without any problem. The holes for the speaker, LEDs, connectors and the LCD touch screen required some precise mechanical works. Since the mechanical elaboration doesn't fit in my current profile, these milling works - based on my previous design, measurements and plans - were performed by a professional company (Metronic Kft.) as a gift to support my project.