This document tries to show those tricks in easy to understand way. The port is very easy to use when you first understand some basic tricks. The PC's parallel port can be used to perform some very amusing hardware interfacing experiments. PC parallel port can be very useful I/O channel for connecting your Notes on different parallel port versions.Notes on parallel port operation during computer boot-up.Parallel port software registers technical summary.Reading the input pins in parallel port input pins.Mains power controlling with parallel port.Building your own relay controlling circuits.Controlling some real world electronics.Parallel port controlling in Windows programs.How to connect circuits to parallel port.We are going to setup X and Y first, to get the servos working, then we will setup the Z axis separately, because it is completely different.For Spanish version click here Parallel port interfacing made easy: Simple circuits and programs to show how to use PC parallel port output capabilities That's not enough for THC, but don't worry, we'll get to that later. Which will leave us with 6 outputs and only 2 inputs for future expansion. If the BOB is just a terminal board that connects signals directly to the pins, then all sorts of problems with signal issues can arise.įor each axis, we will use 2 output pins to control the motor driver, and 1 input pin to detect the home limit switch. Ideally, the BOB will provide features to isolate, protect, and condition pin signals to greatly simply connecting such pins to machines. They can drive a low power LED directly, but to operate mechanical things like relays they need external electronics of some sort to avoid overloading the pin by drawing too much current. Pins have very limited power, so they cannot be used to drive relays or motors directly. And they must operate at zero or 5 volts, with very little margin for error, so a clean stable 5 volt supply is critical for pins to function correctly. Pins are digital, they must be 1 "on" or 0 "off". BOBs often have built in pull-up or pull-down resistors to take care of that. Inputs must be tied to "off" with a resistor, to force the pin to that voltage in the absence of an "on" signal. Inputs should never use open circuits to indicate "off" because a pin that is not connected to anything is like an antenna, it can pick up electromagnetic interference from motors as false signals, or simply float between off and on. Whether a pin should be active-high or active-low is determined by the BOB configuration and the associated control circuitry.Īctive-low is typically considered more ideal because it is more immune to noise and false signals. Pins can be active-high or active-low, which means their "on" state can be indicated by a positive or negative voltage respectively. In Mach3 the parallel port has 12 outputs and 5 inputs.
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