Sconswitch testbench

Serial Controlled Switch

Device description

Device have 32 high voltage open collector outputs, controlled by commands via RS-232 port. Outputs can be in active or passive state and can drive relays, solenoids, LEDs, opto triacs etc. Active state - output transistor open, passive state - output transistor closed.

Device can be used in power control, lighting or any other suitable applications.

Device connects to controlled system via 40-wire ribbon cable and to controlling host via DE9 connector.

Device IS NOT realtime and may not used in time-sensitive applications, e.g. CNC.

Device built on microcontroller ATmega8515-16 in TQFP44 package and drivers ULN2803A in SOIC-18 package.

In firmware part used [KonstantinChizhov/Mcucpp library] (https://github.com/KonstantinChizhov/Mcucpp) and [Peter Fleury UART library] (http://homepage.hispeed.ch/peterfleury/avr-software.html). Firmware compiled by avr-gcc-4.8, pcb designed in KiCAD-4.0.1.

Supported commands

a N|a - Active output number N (or all) p N|a - Passive output number N (or all) t N D - Toggle output N for D (1-255) seconds, press s for stop during countdown n NAME - Output name, set to NAME or unset if empty given s - Show output status h or ? - Show this help

Output status saved automatically to EEPROM with Active or Passive commands and restored when power-up. Commands are not case sensitive. Command line are not editable.

Outputs have numbers from 0 to 31. Toggle means temporary inversion of output state.

Demo video

Electrical characteristics

Supply voltage: 9-15V Supply current: 25mA at 10V Max voltage on closed output: 50V Max current via one open output: 500mA Max total current via all open outputs: 4A (125mA per output and 2x2A per two ground wires in ribbon cable)

Characteristics depend on applied components.

RS-232 mode

9600 8N1

Design Recommendations

• Use short as possible ribbon cable.
• Use only 40-wire ribbon cable, not 80-wire UDMA cable.
• ULN2803 have built-in surge protection diodes for inductive load, but better use discrete diodes, placed as close as possible to coil.