Building a 56k Modem from scratch - Page 1
Forum section: electronics / projects

author: Banned 05.11.2017
author_rank: Contributor
timestamp: November 05, 2017, 03:45:10 am
content: Hi friends,I want to design and build a 56K dial-up modem from scratch, using both analogue and digital as needed. Can you recommend me any reading materials to get started ?Basically I need to convert a serial output into tones, so I expect a VCO or something similar. What do the tones look like? Is it just a frequency for 1 and another for 0 ?After that, I need to connect this modem to my homemade discrete logic CPU and computer serial port via a UART, and then write the software to let me set up a bulletin board system. What kind of work is needed in order to run a crude server on my CPU, so that people can connect to it, download and upload files, read and post messages and so on ?

author: amyk
author_rank: Super Contributor
timestamp: November 05, 2017, 03:55:01 am
content: Start here:http://www.itu.int/rec/T-REC-V.90-199809-I/enThen read all the standards it references, and all the onesthosereference, etc.You have alotof work in front of you... and not to be too harsh, but those who can successfully accomplish projects like this would likely not be asking such basic information here. You're going to have to understand both analogueanddigital electronics, signal processing theory, etc.

author: IanB
author_rank: Super Contributor
timestamp: November 05, 2017, 04:21:51 am
content: Quote from: Engineer321 on November 05, 2017, 03:45:10 amLOL"Hi friends, I want to do something really complicated, that back in the day took hundreds of engineers umpteen thousands of hours to accomplish, and I want to do it myself from scratch without knowing how. Can you tell me how to do it?"Seriously? Do you even know what it took to go from the basic 300 bps modem standard to 56 kps with error correction? And what it took to achieve 56 kps over phone lines with a maximum signal capacity of 1200 baud? (Since they only needed to transmit the human voice with an audio bandwidth worse than AM radio?)And then the work to create a multi-user operating system with simultaneous access by many remote users?

author: amyk
author_rank: Super Contributor
timestamp: November 05, 2017, 04:35:06 am
content: Quote from: IanB on November 05, 2017, 04:21:51 amTo be fair, given that he says he already built a CPU, he could just be trying to follow this guy:http://www.homebrewcpu.com/But those who do such things know that just asking a mindlessly general "how do I do it" question on a forum won't be the way to go; they will ask questions, but only very specific ones, after having done a massive amount of research themselves.I don't think it's beyond reason to think that someone could design a working 56k modem herself; after all, individuals have built CPUs,GPS receivers,LTE base stations, and other tech which we normally think of as "hundreds of engineers umpteen thousands of hours to accomplish" --- but the OPsother project attemptsdisplay a level of aptitude below that required to execute such projects successfully.

author: Banned 05.11.2017
author_rank: Contributor
timestamp: November 05, 2017, 04:40:46 am
content: Quote from: IanB on November 05, 2017, 04:21:51 amAre you here to try and ridicule others (and failing badly) ? It seems to me all you are is a big troll, and not a good one. I think you should keep to your own business if you aren't capable of helping. Afterall you're not even an EE.

author: Banned 05.11.2017
author_rank: Contributor
timestamp: November 05, 2017, 04:43:44 am
content: Quote from: amyk on November 05, 2017, 04:35:06 amYou don't even have a clue of my capabilities and achievements. I think you should keep your humble (and rather idiotic) opinions to yourself. Seems all you're good at doing is being rude and trolling, and I guess that's because you know nothing about what I'm asking but can't resist the temptation of typing bullshit to others isn't it.

author: Banned 05.11.2017
author_rank: Contributor
timestamp: November 05, 2017, 04:47:53 am
content: Quote from: amyk on November 05, 2017, 03:55:01 amI understand both analog and digital electronics. I'm not asking about analog and digital electronics. I am asking about something rather specific called a modem. But I guess you missed that important detail.

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 05, 2017, 04:52:35 am
content: Quote from: Engineer321 on November 05, 2017, 04:43:44 amIt seems to me he was sticking up for you. Maybe it helps to talk about your previous experience and research on the topic, so people can provide suitable information.

author: BradC
author_rank: Super Contributor
timestamp: November 05, 2017, 04:53:16 am
content: Quote from: Engineer321 on November 05, 2017, 04:43:44 amHow about finishing the CPU, discrete video card, keyboard, floppy controller and floppy drive. If you work through the stuff you've already asked about and demonstrate you can get it working people might spend time entertaining some of your vague and un-researched questions.On topic, there are literally hundreds of available papers, documents and patents on high speed analogue modems and how they work. A 2 minute run with a search engine would net you more information than you can easily digest, but asking here after already asking about the aforementioned list of items and not demonstrating any follow through will just make you look like a time-sink / troll.

author: IanB
author_rank: Super Contributor
timestamp: November 05, 2017, 04:55:14 am
content: Quote from: Engineer321 on November 05, 2017, 04:40:46 amThere are questions that have answers and there are questions that don't have answers.Yes, I am making fun of you because you deserve it.If you have any interest in the evolution of modem standards and the history of how modem speeds were increased over time, there is a ton of reading material online. You might at least give some indication that you have researched the topic and you know something about the nature of the problem before you start asking elementary questions. I assume you have reached a level of education beyond elementary school by now?And if you want to know, then no, I cannot help you. I would not know where to start building a 56k modem without spending hours and hours of research into how to do it. And then I would probably throw my hands up in alarm at the magnitude of the problem. If you were to buy a 56k modem when they were common, you would find they have a chip inside them, and the chip does all the magic. The chip took whole teams of engineers and millions of dollars to develop. Anyone wanting to build a modem would buy the chip.Here's the thing: I said the speed of a phone line is about 1200 baud. That is 1200 symbols per second. If you want to do 56k, you need to encode about 48 bits inside every symbol transmitted. That sounds rather difficult, does it not?

author: Banned 05.11.2017
author_rank: Contributor
timestamp: November 05, 2017, 04:57:12 am
content: Quote from: Mr. Scram on November 05, 2017, 04:52:35 amIt seems to me he was mocking my questions. Funny you think he is right and I am wrong. Go on.

author: Banned 05.11.2017
author_rank: Contributor
timestamp: November 05, 2017, 04:59:40 am
content: Quote from: BradC on November 05, 2017, 04:53:16 amIT SEEMS THAT PEOPLE HERE ARE MORE PRE-DISPOSED TO CRITICISING, MOCKING, TROLLING AND DISCOURAGING OTHERS, RATHER THAN KEEPING TO THE TOPICS AND HELPING WHERE THEY CANI GUESS THAT IS JUST THE VILE, DISGUSTING, CHILDISH AND RETARDED HUMAN NATURE.FORGET ABOUT IT. I AM OUT OF THIS MAD HOUSE. YOU GUYS NEED TO TAKE A DEEP BREATH.

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 05, 2017, 05:02:53 am
content: Quote from: Engineer321 on November 05, 2017, 04:57:12 amWhere do I say he was right? Please, hostility won't help your project.Now, what can you tell us about your work so far? Having some idea of that will help us give you suitable advice.

author: Banned 05.11.2017
author_rank: Contributor
timestamp: November 05, 2017, 05:06:19 am
content: Quote from: IanB on November 05, 2017, 04:55:14 amYou seem to me to be a pretty hateful person. You must have been bullied really hard in school, but I guess they didn't bully you enough. Your manners should have been bullied pretty hard, because you deserve it. You have a really negative and bad energy and I can feel it just from your hateful and idiotic messages.You are a big loser, who knows nothing about electronics, and wants to mock others when you yourself has a big empty dummy brain.As you say, you are not an EE, so why don't you go somewhere else ? You seem like a big loser to me, and a total clown. A really big clown. Not even an EE and trying to teach others ? Hahahaha that is hilarious. LOL.How old are you? have you left kindergarden yet, or still getting bullied there for being a dummy ?

author: mariush
author_rank: Super Contributor
timestamp: November 05, 2017, 05:37:01 am
content: Based on the questions you ask in your previous posts on this forum, you are nowhere close to being able to make a modem from scratch. Or a floppy disk... or other things.You also seem to lack the interest in searching for documentation and specifications and trying to figure basic things for yourself and that's something that would turn off a lot of people from helping you. Google search works well, there's also Internet Archive and other services which will have a lot of computer magazines and books in their archives from which you could learn about what you're trying to do.Show something you've started, or even how you've thought of approaching the problem and maybe others will pitch in with feedback and suggestions.

author: gnif
author_rank: Unknown
timestamp: November 05, 2017, 05:57:00 am
content: Topic Locked, this has devolved into insults and name calling