Improving Timex/Sinclair Tape Loading

[Lardo Boffin]

I'm gratified that my little "tape cleanup box" may have a litter of cousins soon.

And it only took us 4 years!

[sirmorris]

The GND connection may not be fully connected in your net. It should probably continue to the negative terminal battery. Eagle complains when power rails aren't explicitly named. I don't know about kicad. The pins 11 & 4 on IC1 might be nominated as power and therefore should only connect to suitably named nets.

I think the original schematic leaves certain details to be assumed. It's for engineers/hobbyists, not computers. The power connections would be implicitly considered.

[Lardo Boffin]

Parts list so far:-

Item.......Link.................................................................................Price.......Qty
C1 to C4 http://cpc.farnell.com/multicomp/mcrr25 ... dp/CA06295 £0.9 For 5
C5 http://cpc.farnell.com/multicomp/mcfyu6 ... dp/CA05016 £0.37 For 10
C6 http://cpc.farnell.com/cornell-dubilier ... dp/CA05876 £1.21 Each
D1 http://cpc.farnell.com/unbranded/1n4148 ... dp/SC07296 £0.47 For 50
IC1 http://cpc.farnell.com/texas-instrument ... dp/SC13781 £0.85 Each
LED1 http://cpc.farnell.com/kingbright/l-483 ... st=Sc11591 £0.72 For 10
S1 http://cpc.farnell.com/unbranded/slide- ... dp/SW03207 £2.11 For 10


Will add the resistors shortly.

If anyone wants to validate this lot that would be appreciated.

Edited to include the LED specification.

[sirmorris]

I normally don't fret about the LED. Pick a nice colour. I like pink! You can change the current limiting later. It may be that the LED is meant to show a valid signal and in this case the current rating may be critical. So go for a bog standard red led, with an iF of about 20mA. If it proves tricky the current limiting can be trimmed with another resistor if necessary.

[Lardo Boffin]

I normally don't fret about the LED. Pick a nice colour. I like pink! You can change the current limiting later. It may be that the LED is meant to show a valid signal and in this case the current rating may be critical. So go for a bog standard red led, with an iF of about 20mA. If it proves tricky the current limiting can be trimmed with another resistor if necessary.

Thanks. Pink sounds good.

Judging by the instructions the LED is supposed to light up when the desired input volume is reached so I suspect it needs to be just so!

[sirmorris]

"However, when pulses appear at the output of IClB, the cathode of D2 is brought low. This causes the output of IC I C to go low and allows current to flow through the LED, thus causing it to glow."

So the led is either on or off, it's not an active component. Feel free to relax.

[Lardo Boffin]

Excellent! Any recommendations (ideally from CPC like the rest of it)? No real idea about these things...

[sirmorris]

Standard red led. forward voltage ~ 2-3v, forward current 10-30ma. Really there's no hard criteria here.

[Lardo Boffin]

Thanks. Have added one that is middle of the road.

[TMAOne]

Standard red led. forward voltage ~ 2-3v, forward current 10-30ma. Really there's no hard criteria here.

Yes anything you can scrounge should do just fine. It's like the black & white stripes--it's just visual feedback, and you get "a feel" for what volume setting works best after a couple of LOADs.

Is the layout from the .pdf really unusable? I took a screen grab and it looks square to me. Heck I drew mine by hand and it works.