PC Serial Port Interface

Below is showed the assembly of a card with 8 inputs and 8 digital outputs for connecting to a PC serial port:

 

Click on the picture to zoom

This circuit is based on the micro controller from Microchip 16F870 and provides 8 digital inputs and 8 digital outputs. You can modify this setup to suit your needs, for example the inputs have been built through switches, but for the case of connecting to an automatic system may be best to insert relays (or opto-isolators) then you will need to slightly modify the circuit.

The card contains the following parts:

  • Power: You must feed the circuit with a DC voltage from 6 to 9 volts, as it uses the voltage regulator 7805.
  • 8 Digital Inputs: are activated when closing the contacts of the switches (you can use relays to manage with external devices based on your needs).
  • 8 Digital Outputs: UN2803 has been used (NPN Darlington transistors) to amplify the intensity of current needed to drive the relay coils. Note that will require external voltage of 12 volts to feed the relay (you can use other voltages if you use other types of relays)
  • A MAX232 circuit to adjust the voltage levels between the PC and PIC
  • A PIC16F870 micro controller that is responsible for conducting management logic and digital signal communication with the PC

You can download the program that you must write on the micro controller from this link:

Compiled program for the PIC16F870 micro controller serial interface card with 8 inputs - 8 outputs

To use this card with EasyPLC you have to select the Serial Port driver and must properly configured. Follow the next steps: select from EasyPLC main menu, Settings -> Hardware I/O, when you get the drivers setup window, select the Serial Port tab, check the Enable Serial Port box, select the Character protocol, type 8 as the number of inputs and 8 as the number of outputs and finally set the correct port number where you have connected the card.

You can buy the PIC16F870 micro controller with firmware of serial card 8 inputs - 8 outpus saved. Send an email to ventas@nirtec.com for more information.