Basically, this device is a simple hardware simulator. It allows you to manipulate the port's data and control lines, monitor the status lines and even send the printer (or other equipment) a 'strobe' pulse.

The idea for the Printer Port Simulator came about while we was developing our Windows-based EPROM Programmer. We struck a rather tricky timing fault and subsequently wasted a fair bit of time trying to work out whether it was due to a problem with the hardware or a bug in the software.

The same sort of problem can occur when you're trying to track down a fault in other kinds of PC-driven equipment, of course. It can even happen when you're getting weird problems with a printer.

We ended up resolving our particular problem by lashing up this Printer Port Simulator. This allowed us to send basic control signals to the EPROM programmer and monitor its status lines, without having to worry about software debugging until later. It proved to be very effective and enabled us to track down the cause of the timing error.

Later on, we realised that our Printer Port Simulator could also be used as a general troubleshooting tool to solve similar problems. So here it is and there's really very little in it - just two cheap ICs, a +5V regulator, a couple of DIP switches to set up the data and control bit lines, six LEDs for status indication, a pushbutton to produce strobe pulses and a handful of other components.

It all fits on a small PC board measuring 113 x 61mm and runs from a 9V DC plugpack. The maximum current drain with all LEDs on is just 58mA.