Магнитофон для Спектрума на ATMega128

[Trol73]

Hi,

I've been trying to force the ZX Taper to record anything from a genuine ZX Spectrum 48K (Iss2) for a few weeks and finally I manage it with a huge support from zipp @ speccy.pl. Now the input circuit is giving voltages as it should.

For ATmega:
- logical 0: 0.2 x Vcc = 0.66V - 5% of safety margin; below 0.6V.
- logical 1: 0.6 x Vcc = 1.98V + 5% of safety margin; over 2.1V

Now the ATmega can recognise pilot, logical 0 and logical 1, save TAP and BAW files. These files can be loaded back to the Speccy. I did also simulations using LTspice for different transistor types like 2N2222, 2N3904, BC847A/B/C, BC817-16/25/40 and it seems that any type can work there.

Hi McKlaud,
I didn't test the device with the genuine ZX Spectrum, but I have the same problem with 86RK (this is a computer from the USSR). The input signal was too weak for ZX Taper.
Thank you and Klaudiusz from speccy.pl for idea about ltspice!
Here is my original circuit


Now I have just changed R7 from 1.5K to 4.7K and R8 from 150 Ohm to 0 Ohm and and the device began to work successfully with 86РК!
So if you made PCB according to my circuit, then it's enough to replace only two resistors.
On the screenshot my changes on the left and yours - on the right:


About C10 capacitor (10nF) - without it I had too much noise on the input. With this capacitor the result is much better. Although it also rounds the front of the pulses on the simulation plot.

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