Edit: RichTheDude, I really truthfully do appreciate that you are actually trying to talk electronics with me and not questioning my ideas or other wise stalling and being difficult for no reason what so ever. The following comments, though possibly hurtful, are not an attempt to cut you down, be little your intelligence, or otherwise be hostile toward you. They are intended to only point out that you were trying to join the conversation while obviously not paying attention to it. Though I can understand making minor bad judgment calls or missing things because of influences like being up way too late. Still, if your honestly trying to help me, then you should try to pay more attention. If this offends you I'm sorry, but these are all facts as much as it is that I thought "discreet" was actually the word "discrete". I accept my failure with honor and have corrected that mistake.
"Develop a circuit which can [put] through from Ethernet to a serial stream of TTL and vice versa"
This is precisely why I'm here, check the post title again. If I was doing something else I prolly would have labeled it differently don't you think?
"I severely doubt the circuit you have posted btw."
That makes two of us. Which is why when I posted it I also said... "it's got more fundamental problems than I care to admit." I was fully aware of it's flaws. And I was never saying that circuit as is would work, merely using it as a reference.
"Make your laser diode and receiver combo."
Done ages ago on the bread board.
"There are laser driving IC's out there "
There sure are, and I still don't care.
"most likely [use] a Si PIN photodiode"
Yep, and make it all reverse biased and such.
"at these speeds turning the laser [fully] OFF to [fully] ON will most likely be too slow."
Yep, QED
"Most communication systems intensity modulate a laser diode"
kinda Like mine did/does/will.
"Also make sure your laser diode has a collimator"
Laser pointer lens modules + CD burner LASER diodes = Close enough for me.
Edit: ===================== Speaking to RichTheDude ends here... General commenting to the community begins =====================
OK, fundamentally the problem at hand is still just how to get the 100base-Tx three symbol 25Mhz information off the twisted pair medium back to a plain Jane TTL 1's and 0's STREAM where it's nice and easy to work with. Not having an adequate discrete solution to this hasn't changed. It's a tricky problem to address with the restrictions of doing it all from scratch and ignoring preexisting parts specifically built for doing this task. This is because we are working in an area that's not quite analog, but not quite digital. It's a grey zone. But I'll start things off with some basic ideas...
We start with the twisted pair medium, we use a differential amp and maybe (probably) a transformer to prepare the information to make it no longer be differential nor contain any common mode line noise. The amp will have to be able to do at least 25Mhz as that's what the 100base-TX standard uses on the wire. After this we need a way to return the three MLT-3 encoded voltages back to TTL. This could be done with two properly biased transistors, An NPN for +1 volts and a PNP for the -1 volts. Lack of triggering either transistor would indicate the 0 volt level of the MLT-3 encoding. So either transistor being activated would deactivate the third (ie logical NOR) This would provide us with three lines at TTL levels. Now some logic to convert this to a serial data stream is needed. This is where things get tricky... Everything up until this point doesn't need clocks or logic gate IC's or any of that fancy jazz, it can all be done with discrete parts. (I consider some 8-pin IC's discrete parts) But the actual information is basically Manchester/NRZ encoded. So it looks like it's going to need edge detection, a high Q clock, and a shift register circuit. That or some kind of magic...
Thoughts on this so far?
Lets continue. Now if all I was after was JUST the LAN-LASER-LAN conversion, I could from this point build a voltage controlled RF oscillator whose oscillations bring my LASER diode into and out of the lasing threshold. Then use the three wires obtained above to shift the frequency of it to higher, lower, and neutral frequencies. Or use some third frequency and leave neutral for debugging, aiming, and/or error correction. Finally use some form of RF filtering and FM detection on the receiver end to demodulate the RF back to the three wires above. From there it's easy to go back to differential, and thus back to 100base-TX UTP. And none of that would require any form of processing or decoding, AND the circuit would be fairly simple as far as I know.
If any one would like to work on JUST this LASER bit, I'd be down for it for the most part. It would be a good first step toward the goal stated in the thread title. And I could still use the device when finished. Even if it's not exactly the main/first topic at hand.
(Edit: THIS COMMENT IS NOT DIRECTED TO ANY ONE PERSON IN PARTICULAR.)
Any grammar, spelling, or punctuation errors are not my fault but are in fact the fault of the English language, If I have made a mistake and it bugs you... PM me and I'll fix it ASAP. Also, post count does not equal the size of ones manhood, nor is an indicator of ones IQ. I've been EEing for a while now. I'm NOT a nub or moron. Just thought I should point this out once more, I don't have a lot of posts because I don't often need help with stuff like this. I CAN do it all by my self.