LOAD INTERFACE FROM CASSETTE FOR THE SPECTRUM EMULATOR 9-08-92



There are two ways to load Spectrum programs from a cassette with the "LOAD" command through the PC centronics port with the emulator from Pedro Gimeno:

1.- directly connecting the wires, like the emulator's author explains in the help file, the brute-force way, with an accompanying high risk for the physical integrity of the computer and the psych of the owner.

2.- using a simple interface that blocks the negative half-waves from the output of the cassette, and limits the voltage below the TTL max level (5.25 volts). Then, using a Schmitt trigger, like the 74hc14, with a threshold of 2.5 volts, we have a wide range in which to adjust the cassette volume, and program loading is similar to that of the original spectrum. However, loading is more sensitive to amplitude variations of the old tapes. To fix this problem, I use an audio amplifier to boost the signal (now without any fear, because the port is protected). When loading problems affect the actual Spectrum, I use a copy program and the amplifier, clean the head and adjust the azimuth to later transfer the data directly from the spectrum to the PC.

The schematic is something like this:

Schematic


The power supply for the 74hc14 is taken from the centronics connector, pin 16 (/int), or pin 14 (auto feed). I use a 10nf decoupling capacitor between Vcc and Gnd of the IC, but centronics ports vary, and the capacitor may prevents correct operation. The unused inputs in the IC may be connected to Vcc or Gnd, to reduce power consumption.

A save section is not possible because the emulator program doesn't have this facility, but I hope we have a save option soon. All this circuitry may be contained in a DB25 connector shell, including the jack for the cassette wires.

That's all. I hope that you can load any of the programs that you don't yet have in your PC, with the knowledge that your port is protected.

Grettings to all spectrumaniacs... and now, TO WORK !!
EB7GWL Home Page