Parallel Port Interfacing in Visual Basic

I don't do VB but the following may help.

The lines are turned on or off by printing a character.

Create a variable to store the current state.

You can then manipulate separate bits and output the changed character.

http://www.lvr.com/parport.htm Jan Axelson's Parallel Port Complete book

If you use 3 of the control lines and only one data line and a 8 bit latch it will be possible to switch each of these LED's separately. You need a 3 x 8 address decoder and a 2 latches.

I have a splitter board here somewhere where 64 LEDs (8 lots of 8) can be switched.

You have to do the VB equivalent of bit-masking and logic programming, ie.

Bit2 AND 223 will turn bit 5 off and leave the others as they are, and

Bit2 OR 32 will turn bit 5 on and leave the others as they are.

where Bit2 is your bit, 223 = 11011111 binary (bit 5 off) and 32 = 00100000 (bit 5 on).

Hope this helps.

Warning!

Be vary careful when connecting to the printer port, you can ONLY rely (unless you have the manual for that PC that states it differently and how much) on being able to source 2.6 ma and sink 24 ma. eg. A typical 7400 output.

Having dropper resistors of less than 2K Ohms (assuming a 5 volt output as some Laptops only have 3 volt outputs) to your LEDs MAY still cause damage.

Many diagrams on the web AND much professional equipment too use lower value resistors with the possibility of damaging the main-board.

Usage of a plug in PCB or PCMCIA Printer port which are both cheap and easily replaced is recommended.

The above warning will not fix the problems you are seeing at this time, (but may save you from other ones!) but the link to Jan Axelson's web page will help enormously.

Depending upon what you eventually want to do, you might want to join a Yahoo group like DIY-CNC-Interfacing to get even more infos and practical circuits you can build for CNC (stepper motor) or Robotics control or whatever....there are plenty of free programs running under DOS, Windows and Linux for such things, you don't need to re-invent the wheel!!

Keep us informed and up to date please.