Parallel link troubles

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Summary:

I tried building one but it doesn't work and I can't figure out why. Can anyone help me or sell me one for cheaper than TI?

Parallel link troubles

ninjabob7 02 Nov 2008 05:38

So I attempted to build the parallel link as shown on ticalc.org. I soldered everything and tested it and it appeared to work. When I ran linktest, it gave this:

send 00 - read 10 - should be 00
send 01 - read 30 - should be 20
send 02 - read 30 - should be 10
send 03 - read 30 - should be 30

I double-checked everything and found that some wires were touching. After insulating everything (which involved re-soldering the ground) I tried again and linktest gave 30,30,30,30 - which is the same as when nothing is plugged in. I also tried the "debug" method with a voltmeter and only detected low voltage on the calculator end.
The only thing that seems like it might be wrong is that the diodes appear to have a resistance of 3K ohms (which seems way too high). They aren't backwards unless the schematic is wrong or they were defective. Even with 4K resistance from input to output pins, there should be some change in the voltage, right?
At this point I'm considering just buying one if no one can help me - my "$5 link cable" cost me $13 so far, but the TI one is $20 dollars! Does anyone sell the homemade kind anymore?

Re: Parallel link troubles

GoVegan 02 Nov 2008 05:55

What is this "parallel link" supposed to do, exactly?

I'm assuming that you did reverse the diode just to check, right? People do make mistakes sometimes… And I'm also assuming that you bought the correct diode… Strange. Maybe you have a faulty circuit board. If possible, you should go over the entire circuit very finely with solder, in case there are any "invisible cracks". That's all I can think of. Oh, you could have a faulty diode aswell. Rare, but it does happen.

Re: Parallel link troubles

ninjabob7 02 Nov 2008 16:01

The parallel link connects the TI-83 to the computer so you can transfer programs. It's called the $5 link, but it actually cost me $13 in parts (not including the $2 they overcharged me). Based on that and all the mentions of 486's and 33MHz's on the website, I'm starting to wonder if it even works with modern computers.
I can't reverse the diodes without de-soldering the whole thing, and I don't have the equipment for that. I seriously doubt that BOTH diodes are defective. When I use a meter, they completely block current in one direction (as they should) but they have a 3K resistance in the other (which I don't think should happen, but it could be less resistance with more voltage - I don't really understand how they work.)
The "correct diodes" - the package has two part numbers, one of which is the same as the plans. I'm assuming they're different numbers for the same thing, because all ten diodes appear to be identical. In any case, RadioShack doesn't have any others.
I also found a USB link for $11 on OfficeMax.com