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Below are the 6 most recent journal entries recorded in DIY Radio/Electronics Projects and Repair's LiveJournal:

Saturday, May 8th, 2010
10:07 am
Hi, noob intro post, don't eat the visitors :)
Hi there,

I'm just about to begin building a small home CNC machine/3D printer (reprap type without the reprap costs), all the electronics will be the same, just the tooling differs, I have no problems with the tooling, it's the electronics I'm not too hot at.

I'd like some assistance with this if any of you has the time/patience for an idiot me :)

What I'd like to do is use my printer port with opto-isolators to direct my machine, but use my PC to do the math.

What I'm looking at is using 4 of the i/o to determine the plane to move, 1 to control the direction and 1 as feedback for end-stops. though I'm still not sure this is the way to go.

Can anyone suggest a simple (and inexpensive) method of controlling 3 steper motors (For plane/direction), and speed of cutting tool (Software will work out speed needed, according to material and tool size) and ideally as many parts as possible should be able to be recoverred from off the shelf goods likely to be easily sourced from the likes of Freecycle/Freegle as I am environmentaly conscious.

Many thanks in anticipation.
Saturday, October 14th, 2006
1:16 pm
Simulation software
Can anyone here suggest a simple to use FREE circuit simulation program?
I'm looking to build some simple LED circuits and perhaps a PWM powersupply in the future. I've found dozens of flavors of SPICE. But they all seem to be like hammering in a thumb tack with a wrecking ball.
Really all I need is the mickey mouse, MS paint, tinker toy level of simulation. Any suggestions?
Monday, October 9th, 2006
3:37 pm
mYpod : CompactFlash-based, in-dash mp3 player
Yay...after all this being too busy, too lazy, or any number of other excuses, one more project finally off my stack. The "mYpod"* is a small CompactFlash-based mp3 player I built from leftover spare parts from a bottom-secret government project, free samples and a standalone mp3 decoder chip.

(Click thumbnails for larger image)


  • Supports CompactFlash media up to 2GBytes officially (FAT16 file system limitation); 4GBytes if you "relax" (i.e. violate) the FAT16 specification a little by setting a 64KB cluster size (Win2k/XP will allow this, but Win98 and below will bitch loudly and not read the card)

  • Actual, real, full FAT16 implementation - handles fragmented files, deleted files, etc. (You'd be amazed how many card-based music players, and even some digital cameras, do not fit this description, or at least not reliably)

  • Playback of mp3s with bitrates all the way up to the maximum mp3 bitrate of 320KByte/sec

  • Display title and artist from ID3 tag if present (display filename if no ID3 present), and elapsed time

  • Saves the currently-playing song when powered off - picks up where it left off

  • Song selection: next, previous, "skip 10", pause and menus (e.g. restart card from the beginning)

  • Buttons light up at night like a glow-in-the-dark Bomb Pop

  • Line-in and line-out from stereo available on front panel (anything plugged into line-in is switched in instead of mp3 player)

An early view of the guts, before they were enclosed in anything

One evening a year or two ago, GJM and I were about to head home from work and talking about part of an environmental monitoring system we were developing at the time. This was a handheld data-retreival unit that queried the environmental loggers in-the-field and recorded their wireless data to a CompactFlash card. I remember jokingly saying, "Hey... we have a memory card, A/D, processor, LCD and buttons...how many extra parts do you think it would take to turn this into a music player?" Next thing I know we've got a couple beers cracked and are laying out a quick-n-dirty mp3 player board in an unused corner of a layout set to go out that night.

Packaging this quick 'n dirty design as a truly portable device would have been non-trivial (and, I got a Creative Nomad as a gift sometime between the start and end of this project); it would be much easier to package it into a car-stereo size enclosure. My car already came with this plastic tray (officially for holding papers, garage door clickers, etc.) bolted into the spare bay where an auxiliary radio component would go (or the bottom half of those huge, double-height stock radios), so I took it out, drilled some holes and screwed the board and extra parts directly into it.

Most of the parts were leftover lab spares, such as the PIC microcontrollers (scrapped from the Real Project because of a silicon defect in the revision we had; they can act unreliably above 4MHz and therefore can't be used in production gear), the membrane keypad and the LCD. The only major extras needed were the STA013 mp3 decoder ($12) and a stereo DAC (free sample from Cypress Semiconductor)** to convert the decompressed digital (PCM) audio from the STA013 to real sound.

Guts during assembly. The large tall chip toward the front, hiding behind the too-fast oscillator (more on this in a bit) is the mp3 decoder, the square 64-pin bitch-to-solder in back is the PIC. (Click for larger image)

For the front panel, I grabbed a piece of Lexan left over from building the terrarium and of course, cut a bunch of holes in it. I started off with the usual score-and-break method of cutting the Lexan, but when it came to inner cuts (e.g. the rectangular holes for the CF card and LCD) consulted my dis-is-how-we-do-it-in-da-ghetto handbook, laid a hot soldering iron against the back of my X-Acto knife blade and pressed it into the piece. Like a hot knife through buttah! Using a straight edge as a guide, this provided straight, clean cuts, which were touched up a bit with a small hand file. Round holes were cut by making a pilot hole with a small drill bit, working up to larger and larger drills until the desired size was reached. The Lexan has a tendency to grab the drill bit and suck it in (depending on the intricacies of classical physics, this either yanks your drill out of your hands and into the piece, or yanks the piece out of whatever's holding it, potentially snapping it), so don't go diving immediately in with the large bits.

The keypad features an adhesive backing and insertable overlay for the button graphics - being the perfectionist that I am, I doodled some arrows and symbols on a piece of paper and slid it in. Since the front panel is clear, and surprisingly, the buttons themselves are translucent, it was easy to stick a few colored LEDs on a piece of Veroboard behind them, angled and distanced so that they cast a tight circle of light on the entirety of only one button each. I was originally going to have this turn on automatically when the headlights were turned on, but couldn't find such a signal on the radio's wiring harness. The LCD unfortunately comes without any backlighting, and no way in hell to add any since it's mounted flush against a very opaque PCB full of traces. A metal guard ring completely surrounds the glass; if removed, the glass ceases displaying anything and falls out (the metal band presses it tight against a zebra strip that connects it to the board).

The button panel, without sexy backlighting. You can see how much effort I spent on it! ;) (click for larger image)

Software / Featuritis:
A couple features are missing, either because they were accidental, or too much of a pain to implement. The most notable is fast-forward. The firmware is already handling FAT16 fragmentation transparently in the background; all the decoder requires is bits, as fast as you can stuff them in. Mp3 files are made up of many small time segments called frames, which often incestuously share bits with previous frames, so you can't just play the file at 10x by dropping 9 out of every 10 frames. All you get from this is a bunch of blips and pops... fast-forwarding an mp3 turns out to be non-trivial, so it is not implemented here. The other non-implemented "feature" is Chipmunk Mode. The mp3 decoder runs off of a very precise master clock, typically around 14MHz. Following this (internal to the decoder) is a Phase-Locked Loop system of clock multipliers/dividers that can be software adjusted to provide a correct timebase from a wide variety of input clocks. While I was testing, I got the sensation that everything from my player sounded a little "sharp". Indeed, a side-by-side comparison between the early mYpod and WinAmp confirmed that the same 3.5-minute song finished almost 10 seconds faster on mYpod. Turns out I had the PLL set for a slower master clock than I used, so it was playing back too fast. I discovered the PLL settings are very, very adjustable; you could make all your favorite artists sound like demons or chipmunks. Unfortunately, this is not exactly a "fast-forward" feature (by the time you speed it up enough to be a decent FF, it's too high and whiny to be intelligible - besides, the micro can't pump data out that fast anyway), so I set the correct speed and didn't leave provisions for messing with it via the front panel.

For the firmware - that was actually the most annoying part of this project, a lot of assembly coding. The FAT16 stuff was actually written already for the most part, as part of the actual work project (otherwise, I'd release the code here). All the fiddly bits (buttons and menu system, LCD scroller, play timer, hunting for ID3 tags, position-saving hack to an already crufty file handler, etc.), and getting them to play nice with one another (e.g. does the play timer stop when playback is paused? What's the easiest way to restore the song title/info on the LCD after it's been overwritten with a menu?), still had to be done though. The PIC programmer supplies and requires 5V to program, but the mp3 decoder chip can only handle 3.3V. The solution to this was to load the Jolt serial-port bootloader onto the PIC before soldering the decoder in (and hope I never introduced something in my code that overwrote the bootloader). Sending new firmware over the serial port, the PIC can self-program at 3.3V.

Last but not least, this beast had to be connected to the headunit somehow. Pioneer decided that all good headunits should have line-ins, but ensconce them in this proprietary 11-pin "IP-BUS"*** connector (with differential inputs, no less). Bah. Luckily, breakaway pin headers plus heat shrink equal reasonable facsimile of funny plug, and the differential inputs work fine by just dumping single-ended signal into one side and grounding the other.

So yeah... it sounds good! Now I just need to put the TrashAmp back together (strip away the melty bits, etc.) for that phat window-rattling bass, yo.

* my brother calls it my mpthriller - then again, he's got some shizzle on his nizzle.

** I only sampled it because I couldn't get it from Digikey or any other decent distributor. Ohh, that was a mistake. Samples came at a cost of about 6 months of horny Cypress rep calling me about how the chip's working out for me, when he can come over and show off the full product line, and how soon I'll be ready for those 10,000 units...

*** as in like, Intellectual Property Bus? As in, if any competitors try to reverse-engineer our funny plug and make something compatable, there will be hell (or IP lawyers) to pay? All right, maybe it stands for "Interconnected Peripherals" or something.

Posted to: gadget_design, diy_electronics
Monday, September 18th, 2006
12:13 pm
Recovering a cassette
Hi, I'm in the (lengthy) process of converting all my vinyl and cassettes to mp3, and I have a problem with one particular tape.

It's an old demo of a Melbourne band called the Editions, and due to being played on crappy cassette players for many years, the tape is really badly wound (ie it has those little "ridges" where part of the reel of tape sits up higher than the rest), to the point of being unplayable.

It forwards and rewinds easily enough, but when I actually try and play it, the tape gets to a point where it plays r-e-a-l-l-y s-l-o--w---l---yyyy and then just stops fast. Nothing I do can get it to play past that point.

I've tried forwarding it back and forth a few times, taking it out of the cassette case and smoothing it down with the flat of a butter knife, and putting it back in a better case (a TDK SA90), but no dice.

I really really want to rescue this tape, as it's very hard to come by, so if anyone has any suggestions, I'll be eternally grateful.

X-posted to a whole bunch of places.

Current Mood: annoyed
Wednesday, August 23rd, 2006
3:17 pm
I'm about at my wit's end since I've googled practically until my eyes bled. I've viewed the sci.electronics.repair entries regarding monitor repair but I find nothing specific about the actual process of safely and successfully repairing an input cable. I've basically got a 15" Mag Innovision LT501 that I got from my stepfather, who bought it some years ago. Everything (with the exception of the cable) on the monitor works, the video card is seated tightly, etc. It's just right at the male input plug, near the little cylindrical block on the cord that you have to move the cable in order for someone to get the colors to display correctly. Otherwise, it just shows one color (depending on the orientation of the cable relative to the computer) or goes blank. This has lead me to the logical conclusion that the connections between the wire and the pin is weakened/loose (something of that sort). I'm trying to get ahold of someone in the company that handles tech support for Mag but it's slow going so I have no idea if I can find a replacement cord or not. Near as I can figure, I need to slice open the outer cord and the shielding, break open the plug?, get the wires reconnected (soldered and such).
Is there -any- guide on doing this in a manner that I can reliably seal up the result and have it work? Any documentation someone wrote while they did something similar? I just simply can't afford a new monitor right now.

Saturday, December 17th, 2005
11:39 pm
I'm still in the process of setting up the community (description, icon, etc).

In the meantime people can post about their projects, questions, and concerns because it may take some time before I put the community description and rules on the profile page.

Rules: No eBay listings. Millions of people look at eBay daily. There is no need to advertise your eBay listing here. If I see an eBay listing I will delete it. If someone mentions they are having trouble finding a tranformer, tube, transistor, or other odd part and another member has that item, the two members are free to trade contact information and arrange a sale or trade, preferably offline.

Well, that is one rule. I will add others if needed.

Anyway, about me: I'm an electronics addict. Have a ham radio license and interested in VHF/UHF primarily, although I haven't been on the air much because I'm in an apartment.

I often wander through the thrift stores and yard sales looking for inexpensive radios. I prefer to buy non-working equipment to fix. I guess it is the challenge of figuring things out without a schematic, unless I can find a schematic on the internet.

Recent acquisitions:

Realistic Modulaire 8 - 8-track player with AM/FM stereo. Someone tossed it into a pile of trash. I came across it walking in the rain a little over a week ago and took it home with me. I let it air dry for a few days, and plugged it in. A light came on and a horrid hum came through the speakers. After replacing the filter capacitors on the power supply it works fine. I cleaned it up and it is in fair condition, but the brushed-aluminum face has a few scratches, probably from being tossed into the pile of debri I pulled it from

Vintage Calculator - I came across a TI "Spirit of '76" Commemorative Edition (1976 Bi-centenial) calculator for $1.00. It looks like most of TI's calculators from the mid-70's, but the case is white and the background on the keybad and a Commemorative 1776-1976 them. It works, but number 8 on the keybad does not always work. If anyone knows of a fix for old calculator keybads, please post (that is what this community is about).

At the same yard sale I also picked up a Pioneer CLD-2070 CD/CDV-Laserdisc playe (Made in 1989) r for $5.00. It works, or at least it is playing CDs and sounds good. When the drawer opens there is a bit of noise. I think a belt may be worn, or something lubricated is gummed up. I'm thinking of buying a few laserdiscs on eBay. Maybe Pink Floyd's "The Wall."

About a month ago I bought a Sony STR-D615 A/V Control Center at a thrift store. It was priced $2.00 with a sticker that said "no workee" I plugged it in at the thrift store and front would light up, then the unit shut off. I figured the transformer in it would be worth the $2.00 for another project. I got it home, plugged it in and it worked fine. It turned out that it shuts itself off if the audio amp doesn't have a load. I also bought a Sony CDP-590 CD Player for $4.00. It lit up, but the drawer appeared to be stuck. I figured it could be a belt slipping. The belt was bad, but that wasn't the reason the drawer wouldn't open. The circuit board behind the front control panel was cracked in several places. I think someone go in it at one time and didn't know how to remove/reinstall the circuit board and cracked it. I used the wired from a bad IDE cable to jump the cracked traces on the board and it works. It is particularly sensitive to bumps/skips. As of this time I haven't figured out why.

I also bought a pair of good Sony U560 speakers at a thrift store for $40. Well, $40 for the speakers, a Soundesign receiver and a matching Soundesign cassette deck. I wanted a reasonably good set of speakers, so I just bought the package. It is still a good price, but I can't help but wonder what possessed someone to bundle a 5-watt Soundesign system with 100-watt Sony speakers. At least the Soundesign components are in excellent condition. Maybe I can sell them to someone that is into that "totally 80's" look, complete with flashing LEDs all over the front panels.

At one of the thrift stores here that has a tendency to overprice things I came across an Optimus CD player for $7.00 in very good condition, so I bought it. No problems with it. I think the person that priced it thought Optimus was some ultra-cheap junk brand from China. Optimus is one of Radio Shacks brands. I have found most of there stuff to be of better than average quality, so if you see any Realistic/Optimus/Archer/Radio Shack Products prior to the brand's manufacturing being outsourced to China, consider it a fair value if the price is right.

Other things: I have several desktop and clock radios with tubes. Quite often they are disposed of because they hum. Replacing the filter capacitors usually resolves the problem. I also like vintage audio equipment. I use a Pioneer SX-424 (made in 1972?) in the back room. I can't remember what I paid for it, $4.00, I think. The thrift store was going to trash it because someone blew it up. I offerred $4.00 for it thinking I would have to replace a few audio outputs, but it turned out that the fuses blew (always fuse audio outputs). I'm working on getting a few more early 70's things. I have a really nice JVC-Nivico 8-track player (made in 1971), several portable radios I use for DX (the ones made now can barely pull in the local AM stations). Several Voice of Music products, a Heathkit tube FM tuner, and I recently bought a Dynakit Dynaco FM-5 that was partially assembled and in a box. It is not working because someone didn't assemble it correctly. I do not have the manual, so I will have to acquire that before progressing further.

I also have several Pioneer cassette decks in need of parts. It looks like one of the parts will end up costing $13.75. The other one is better deck that I haven't opened up yet, but the problem is likely to be a worn belt.

If it seems like I have an abundance of Sony products, I do. The stuff I have decent quality. I use it because I got it cheap. I really prefer Pioneer over Sony though.

Future projects: Tube audio amp from scratch. I haven't decided if I'm going to make a stereo amp, guitar amp, or something else. I guess I'll get around to it when I get over the price of output tranformers.

And yes, I have too much stuff.
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