Is described below in more detail the operation of each of the PCB boards that form the virtual PLC and the principle of operation of each of the main components.
Main Board
The main board is controlled by PC through the RS232 serial port through which receives the clock and control signals in addition sending and receiving data from the respective inputs and outputs in serie format.
Main Board
The main board is controlled by PC through the RS232 serial port through which receives the clock and control signals in addition sending and receiving data from the respective inputs and outputs in serie format.
This board contains 4 integrated 4021, connected in cascade, that work as parallel-to-serie converters, these integrated periodically collect the information in the status of inputs and send them to the PC after conversion to the serie format.
Another 4 integrated 74HCT4094, also connected in cascade, are also shift registers that run, in this case, as serie-to-parallel converters.
hey have a circuit of memorization of state for each output (latch).
These circuits receive the PC information in serie format, decoding it with the help of the control signals sent by the PC and also activate the output that the monitoring program designate.
The diode D1 to D3, with the respective current limiting resistors R1 to R3, limiting the levels of signal from the port series, which normally are +12 V and -12V, 4.7 V (value of zener) and -0,6 V (voltage of zener barrier polarized directly).
The LEDs D5 to D36 and respective current limiting resistors, allow the visibility of the logical levels that exist in 32 outputs.
The 32 inputs have their polarization resistors for showing a logical high level when not in use.
The supply has an integrated voltage regulator, +5 V, 7805.
The 1N4001 diode protects against inversions of the circuit voltage.
Output Interface BoardAnother 4 integrated 74HCT4094, also connected in cascade, are also shift registers that run, in this case, as serie-to-parallel converters.
hey have a circuit of memorization of state for each output (latch).
These circuits receive the PC information in serie format, decoding it with the help of the control signals sent by the PC and also activate the output that the monitoring program designate.
The diode D1 to D3, with the respective current limiting resistors R1 to R3, limiting the levels of signal from the port series, which normally are +12 V and -12V, 4.7 V (value of zener) and -0,6 V (voltage of zener barrier polarized directly).
The LEDs D5 to D36 and respective current limiting resistors, allow the visibility of the logical levels that exist in 32 outputs.
The 32 inputs have their polarization resistors for showing a logical high level when not in use.
The supply has an integrated voltage regulator, +5 V, 7805.
The 1N4001 diode protects against inversions of the circuit voltage.
This board has 8 relays of 24V and can command up to 8 different devices.
It connects to the main board through a 20 pins IDC connector.
To reconcile the signals of 5V the shift registers with 24V of relays, was used an integrated ULN2803, fed to 24V, with 8 inputs and outputs and the ability to supply current to the excitement of the relays.
The main board holdsup to 4 output boards, for a total of 32 outputs.
Input Interface Board
It connects to the main board through a 20 pins IDC connector.
To reconcile the signals of 5V the shift registers with 24V of relays, was used an integrated ULN2803, fed to 24V, with 8 inputs and outputs and the ability to supply current to the excitement of the relays.
The main board holdsup to 4 output boards, for a total of 32 outputs.
Input Interface Board
The board of input interface is built based on 8 optic coupler isolation for the circuits on outside.
Therefore it has ability to 8 independent inputs and connects to the main board, as the board of outputs, through a 20 pins IDC connector.
The main board holds up to 4 input boards, for a total of 32 inputs.
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