Serial Link Help

leofox · Posted: 05 Apr 2005 12:57:37 pm Post subject:

So.. I made my serial link (AKA $4 link) following the instructions from ticalc. But now, it doesn't work. When i plug the cable into the calculator (without connecting the computer) nothing happens. This looks OK, my 'official' serial link did the same.

But when i connect to the computer, the calculator crashes (the cursor stays black and the calculator doesn't react if you press a key). The LED shines all the time though. If i send something using TI-Graphlink, it acts like no cable is connected.

What can be the solution to my problems?

Arcane Wizard · Posted: 05 Apr 2005 01:05:00 pm Post subject:

If none of the wires are touching/connected where they shouldn't be, it's probably one (or both) of the diodes being connected the wrong way round.

leofox · Posted: 05 Apr 2005 01:26:26 pm Post subject:

If the diodes are connected the other way around, the calc ALWAYS freezes if the cable is connected, not just when it's in the comp.

Maybe it's the LED. Led's are diodes too right? Is the LED supposed to always shine?

Arcane Wizard · Posted: 05 Apr 2005 02:33:20 pm Post subject:

Light Emitting Diode

I think it was supposed to stay turned on, and flash on activity.

leofox · Posted: 05 Apr 2005 02:43:22 pm Post subject:

i don't see what else could be wrong...

I guess that's my only chance, i'll try tomorrow.

Ray Kremer · Member Joined: 16 Feb 2004 Posts: 237

There's an old thing with the Graph Link cable where if it's not pushed in far enough the calculator slows to a crawl, including the cursor looking like it's not actually blinking.

Arcane Wizard · Posted: 05 Apr 2005 05:13:49 pm Post subject:

DigiTan · Posted: 06 Apr 2005 01:33:13 am Post subject:

I couldn't get my serial to work either and it's been causing a major headache.

Since no one's said "fire" yet, I'm guessing you used actual zener diodes and not the standard switching type? Somebody should document what the LED is supposed to do so we can know it works. Neutral

leofox · Posted: 06 Apr 2005 09:28:08 am Post subject:

i went to the shop and asked for zener diodes 4.7V, i'm pretty sure they gave me those. On the schematics it says that the triangle part of the led has to be connected to the com-port. In my cable, the long side of the led is connected to the com-port. I'm not that sure if it's the same.

Do i need special software for home-made cables? I used TI-Graphlink, and i can;t get TI-LP to work.

What does LED with 2v voltage drop mean?

Ray Kremer · Member Joined: 16 Feb 2004 Posts: 237

Arcane Wizard · Posted: 06 Apr 2005 02:20:10 pm Post subject:

If you're not sure, assume you're wrong.

About the voltage drop, there's a difference in voltage between the anode and kathode of the diode, with that LED it's 2V.

Unlike other diodes a zener diode allows current to flow in both directions, which is why it's so easy to think the cable should be working, but only if it's higher than it's zener value (0.7V) after which you need to limit the current with a resistor or the diode could easily melt.

leofox · Posted: 06 Apr 2005 03:07:33 pm Post subject:

alexrudd · Posted: 06 Apr 2005 07:53:26 pm Post subject:

Arcane Wizard · Posted: 07 Apr 2005 03:21:31 am Post subject:

Heh, it's kathode in Dutch, must've slipped.

Yes, that's normally the point, just not with zener diodes and I think one other kind of diode.

I'm not sure, but I think there's still a voltage drop between the cathode and anode with the zener diode, so that they're not completely useless.

DigiTan · Posted: 07 Apr 2005 11:40:55 am Post subject:

Yep. The zeners will keep the link voltages under 4.7v on the calc side, instead of the +/-25v from the comp. There's really no reason for why ours link shouldn't be working so I think it's the PC settings.

I told some DS guys about the problem, and they said it might involve the BIOS settings.

leofox · Posted: 07 Apr 2005 11:47:57 am Post subject:

Oh crap, my BIOS sux. It only shows what key i have to press for .5 seconds, and it's different from normal bios, cuz it's DELL.

I'll try though..

Ray Kremer · Member Joined: 16 Feb 2004 Posts: 237

If the BIOS settings is all it is, that's relatively easy to take care of.

http://www.technicalc.org/tifaq/?p2.htm#4.4.5

leofox · Posted: 08 Apr 2005 02:25:15 pm Post subject:

My official Serial Link worked earlier on the same port and everything, on multiple computers. I've tried my link on 2 computers, both of which worked with an official link in the same com port, and it didn't work.

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