or... wandering around the house, finding stuff that any normal person would have thrown out decades ago.
Take a walk down memory lane with me!
Many of these photos were taken in 2010 -- so the subjects don't look quite as nice as when they were built (:>).
The earliest thing I can recall constructing was this opaque projector. I seem to remember being in the third grade, which would put it in 1963:
I remember building this crystal radio in 1966:
Other early projects: I built lots of stuff from Alfred P. Morgan's The Boy Electrician which I found in the library. A pdf of the book is here. I definitely built the microphone which is shown on page 175, but it wasn't quite like he shows it: I cut open two D batteries and removed the center carbon post (did a lot of that). Mounted them horizontally on the top of a cigar box, and laid a length of mechanical pencil graphite across the two posts. Then just put a battery and headphones in series with the contraption. I remember showing it in fifth grade, so that would be 1965.
I built the transformer shown in page 226. It seems crazy, because in the 1960's you wouldn't necessarily find the kinds of stores Morgan wrote about originally in 1913! But I found a sheet metal shop within walking distance, and the guy cut up hundreds of rectangular pieces for me. Couldn't have cost much as I was a little kid. Somehow found the copper wire, too. After building that one transformer, I decided I'd just get ready-made ones in the future.
Built many electromagnets (remember the large cylindrical 1.5 volt batteries with thumbscrew connecting
I did make a "bullhorn" which was a transistor amplifier wired to a speaker. I was definitely not impressed with the loudness, it was probably 100-200 milliwatts.
I had an intercom system on several floors of the house, probably when 11-12 years old.
Speaking of transistors, I struggled to understand them. All the books said you put current in the base-emitter junctions, and you got amplification at the base-collector pins.
I don't know how many transistors (they were all germanium in those days) I blew out in the 1960's, because I put a battery directly between the base and emitter (properly forward biasing it) and a DC motor at the base-collector;
I expected the motor to turn faster than without the transistor. Never happened. Eventually I learned the difference between power generation and control modulation!
I seem to have been fascinated with breaking down aqueous molecules with electrolysis. I have a spiral notebook with entries dated April 7, 1967 through February 24, 1968 -- 72 handwritten pages in all. I filled gallon glass jugs with hydrogen, oxygen, chlorine, and who knows what other gases. You know the hydrogen test of putting a match under a small inverted test tube and getting a crack or popping sound from the combustion? I did that with gallon glass bottles and got a big (BIG) wooof! and lived to tell with no mishaps... mishaps... mishaps
This doesn't really belong in this section, but it's chemistry. In Drew Wolfe WA3KLK's high school chemistry class, we fermented various fruits and distilled the mash into wine. But I double-distilled (maybe triple?) mine! The result was probably near 100% ethyl alcohol. "Teach" advised us not to sample our wares, we were aware of potential serious health issues. But we were high school kids! Are you kidding me? I did take one sample (back then) and found it to be quite potent. I was already wearing eyeglasses and didn't become any more blind. This is the actual booze.
Yes, yes, I know -- you don't have to tell me. The fact that I still have this proves that I'm certifiably crazy!
Originally I had an old large pressure tank, and lots of salt and neutralizer equipment for my well, all from the original construction in 1966.
Automatic Well Pump Shutoff
I had a bad pipe leak and it ended up filling the basement with water before I noticed it and shut off the well pump. So, like closing the barn door after the horses had escaped, in September 2010 I installed an automatic well pump shutoff system. I bought a Basement Watchdog Water Alarm ($10 at Home Depot). It operates off of a 9 volt battery and has contacts on its bottom (which can be detached from the unit). When water on the floor is detected, it emits a high-pitched warning sound. I was very impressed: with no alert active, my DVM could measure no current drain! So it was less than 0.1 ua. It draws about 13 ma. when active. All in all, quite power conservative.
I also put another Basement Watchdog by the basement door to alert me in case my outside pump gets clogged up. I used an AC adapter to power it instead of a battery.
The heating element in that water heater opened in September 2010, 18 months after installation. The warranty is for one year. Concerned that this might be a recurring problem, I phoned tech support. Apparently they had made some unspecified changes in the design, and they sent me a free replacement element. Actually quite easy to repair the element anyway: the resistance wire (like a toaster's coiled spring) broke at the mounting screw. Just re-wrap on the screw. So I now have a replacement ready for next time.
There is a long pipe run from the main water heater to the upstairs bathrooms, and it always took a good two minutes to get hot water there.
Originally there was a small electric tank heater in an alcove behind a bedroom closet (above right) which was fed from the main heater.
Only a few feet from the bathrooms, this gave a fast heat response. Too bad that heater had been broken for many years.
I would have replaced it eons ago, but all of the fittings were corroded, and access to the tiny spot through the closet made me fearful that I'd make
matters worse if I tried to remove it. But the EX95 in the basement doesn't have enough oomph by itself to satisfactorily power a bathtub fill or shower.
I took the opportunity to finally address the small water heater failure by replacing it with an Eemax EX65T tankless unit. This device is microprocessor controlled (PWM) to maintain a constant output temperature.
(The EX95 isn't, it heats the water as much as it can as it flows.) Necessary, because it is fed from the EX95 and the two together could possibly boil water.
It draws 27 amps @240 VAC (another 6500 watts!). I put a low-flow aerator on a bathroom sink which manages to provide just enough flow to activate the EX65T,
but is below the activation threshold of the EX95. Which accomplishes two things: (1) it saves power, because the main unit is not turned on (which would be useless anyway
because you finish handwashing before the hot water makes it upstairs to the sink); and (2) it keeps the flow rate low enough so that the EX65T by itself can heat the water sufficiently.
It's still necessary to wait a couple of minutes for both heaters to contribute to showers or tub fills to handle those rates. In all, this combination has proved satisfactory,
though not really quite as good as a tank heater. To be fair, the EX units are not rated for whole-house usage, but the stronger unit takes three 240 VAC 40 amp feeds,
which would have been more aggravation at the circuit panel. As it was, I was able to re-use the 240 VAC line to the main water heater
but had to run a new 240 VAC line to the EX65 (there was only 120 VAC in that location).
Basement Doorway Drain
My basement doorway has a drain, but where it goes, nobody knows. It does work after a fashion, but usually quite slowly. During heavy downpours the stairwell water level rises until it sometimes goes over the lip and leaks into the basement proper. I've bailed and mopped not that often, but more times than I'd prefer! In July 2009 I bought a central air conditioning condensate pump. I cut out a hole at the bottom on the box's side and covered with a filtering screen. Attached more ballast (35mm plastic film cannister) to its internal float to get it to trip at a lower water level than normal, and adjusted the microswitch activation hookup to change the hysteresis amount. Had to install a 120 VAC outlet outside the door, too. There's a plastic hose that takes the outflow away from the stairwell. So when the water level rises (but not to the lip's height) the pump activates and pumps the water away until it leaves a small residue. It works fine, but the biggest problem is that I have to clean it every once in a while or it gets clogged up with dirt prevalent in the woods.
In 1983 I put self-stick vinyl tile down on the unfinished basement clubroom cement floor.
Then I put up faux brick wall paneling in the clubroom to match the actual fireplace brick. Thankfully, the studs separating the clubroom area from the rest of the basement were already there.
Installed a bunch of fluorescent light fixtures on the ceiling.
At the end of summer 2008 home remodeling, replaced every single door knob, lock, switch/outlet cover, and doorstop in the house:
I believe it was in eighth grade shop class (1968) that I made these:
In 1983 I used my scroll saw to carve out this wooden road sign.
Painted it with fluorescent orange paint -- it was illuminated at night with a (regular) floodlight.
Even though I had layered it with protective spray lacquer, it needed regular repairs due to wood deterioration from its location in the damp woods.
Eventually it decomposed so much that I replaced it with a metal version.
Main Feeder: I went through a variety of feeders on the dogwood tree at the front of the house.
I started with a simple purchased one that looks like a birdhouse (in the center post feeder shot, below). The squirrels happily sat on it and finished its contents off.
I then tried a commercial "squirrel proof" one that just gave them a convenient cage to hold onto.
I tried blocking the treetrunk with surrounding sheet metal to prevent the squirrels from climbing up to the feeders. Had to keep expanding it until it actually worked, but it looked extremely unsightly.
Additionally, some brave squirrels climbed up adjacent trees out to overhanging limbs and attempted to drop down to the feeder. They sometimes made it and sometimes missed --
plummeting maybe 60 feet or so to the ground -- dazed, yet unfazed. I really didn't feel comfortable encouraging animal suicide, though. I abandoned the blocking tactic.
Then I started fashioning my own feeder construction attempts:
You can see this arrangement just gave the squirrels a convenient sitting place to eat. But I was almost there, the salad bowl needed to be attached to the seed cavity and free from the tray. I determined that the feeder requirements were: (1) there must be nothing for squirrels to grab or hold on to; (2) the top must be large enough to fully prevent them from reaching down; and (3) it should hold more seed to make it last longer between refills, because taking it down was cumbersome. So in September 2002 I designed an entirely new one out of plexiglas (acrylic plastic) from scratch:
The inverted pyramid container directs all of the seed to the bottom feed holes; is large enough to hold 25 pounds of birdseed (which lasts 4-8 weeks); and provides nothing to grasp. The tray is plexiglas, much stronger than the ceiling panel. I added clear moulding edges (with spring releases to flip down when squirrels jump to it) to trap fallen seed. The pulley/weight system is retained, but the separator (salad bowl) is attached to the top section and not the tray itself -- when the tray drops down, there's nothing to grab. Originally (above left) the roof was the same size as the bottom tray, but I modified it to provide an overhang on all sides to make it impossible to drop down onto the tray (two right photos). Initially the weight was a plastic container filled with counterbalancing rocks, but it was unsightly. The final configuration is at the right, filled with aquarium rocks and fake seaweed. I also suspended it with a double rope through pulleys on the tree branch, so I can hoist it up and down for refilling. The squirrels occasionally jump onto the tray, but they immediately fall off. Success! It has remained unchanged since the beginning of 2003, except I redid the roof with quarter-inch thickness material -- as it had to be strong enough to withstand the weight of a foot or more of snow.
Post Feeder: I also put some birdseed on a tray I quickly attached to the entrance post lamp.
At first I just attached it to the side of the post with wire, and of course the squirrels just walked right up the post and sat on the tray.
So I added some sheet metal to the sides and surrounding the post to prevent them from climbing up or grabbing on when jumping from the ground, etc. (left, 8/2003 shot):
You needed a special sense of humor to appreciate this in the 1960's/1970's:
We were buying key systems from T.I.E. in Connecticut -- the KSU's (main phone box) had to be put together with wirewrap dependent upon the installation's requirements, but the circuit boards were ready-to-go. Initially my job was to build and then design simple modifications to the standard T.I.E. gear. This included an interface to permit callers on hold to hear a radio station or a tape deck instead of the built-in mechanical chime; ring a bell (a really loud bell, enough to wake up the dead) for warehouse operation when the phone rang; conference units, etc. Later I tried my hand at designing speakerphone circuitry, with a modicum of success, but not really good enough for commercial usage. Here are my various schematics.
The brothers who owned the company seemed to have some trouble differentiating real business matters
As a second-year EE student, I was very happy to be designing circuits with operational amplifiers (which I had just learned about from Prof. Westgate's class) and I probably wasted unnecessary time with all that.
But they didn't care (as if they even knew), because they were paying me so little (but still a few pennies more than I had been getting sweeping floors!).
I had digested in detail every single T.I.E. schematic until I understood precisely how the phone systems worked.
Which really wasn't required to build, install, or maintain them.
The owners (two brothers from New York) supposedly acknowledged my capability by making me
I remember one particularly humorous maintenance call: #2 brother had gone to one of our customers and tried to get him to pay his bill. He wasn't having much luck, so he went over to the KSU and started randomly pulling out circuit boards. Of course, the phones started going dead all around the office. Needless to say, the tactic worked and the customer immediately wrote out a check and begged to get his phone system back up. The #2 brother might have been a good salesman, but he had no technical knowledge whatsoever. And he began plugging cards back in without considering that in fact they are supposed to go into particular slots. So he burned out the whole thing. That was a service call I took, quite happy to simultaneously be correcting a boss' ineptitude while getting the higher salary!
Later on, as the company failed (the brothers treated it more as a personal playground rather than a serious business) and the workers gradually departed (which tends to happen when paychecks bounce), I ended up doing all of the company's maintenance -- and they did in fact pay me the higher rate all of the time. As the very last employee (I myself had to resort to some trickery to get my final pay from brother #2), I carried a beeper with me to class (in silent mode) and checked in on service calls in between lectures. This was before beepers became commonplace devices for drug dealers and tethered children (long predating cellphones). When that experience was over, I vowed never again. And I never did.
In a strange Twilight Zone type of quirk, years later when I ended up at Telesaver, they moved into the exact same office space that Sonaphone had a dozen years earlier inhabited: 20 Gwynns Mill Ct.
There was no connection whatsoever between the two businesses (other than me, and I had nothing at all to do with location selection).
I had a bunch of the leftover Sonaphone stick-on aluminum labels which I made various uses of, including small heatsinks. I thought it was funny that there were two misprintings on them:
the city name, plus we were the only U.S. company with an 11-digit phone number!
I built two versions of this automobile alarm system:
Every digital dabbler must have a Logic Probe:
You can never build too many power supplies:
Beat the Reaper
Steve writes: I remember a very raspy buzzer, with a 12" diameter 35mm film can as sounding board, which was triggered on timeout or when the wand hit the wire.
The control circuit was built around a thyratron (2D21) controller from my junk box.
I remember a length of RG-8 shield, at the end of the wire and insulated from it, which the customer touched to trigger a success indicator. However, I don't remember what that indicator was.
It might have been a Mallory Sonalert (I agree). I can't find the schematic either.
I remember visiting the shack in 1985, shortly before it was leveled to make way for the sculpture garden.
The Reaper tubing and poles were still there. The club was inactive, and the place was in tatters. All the gear within about 2 feet of the floor was ruined, though, by a flood.
Marc Leavey WA3AJR was a real (original) Trekkie, and he wanted a Communicator.
I designed a circuit for him which mimicked the sound the TV show's devices made when flipped open.
At the right is the initial version of that circuit. He constructed a pretty good imitation of the icon and built in the circuit. Cool (well, back then it was! Remember, this was before cellphones.).
published an article on it in the February 1976 issue of 73 Magazine. It was made into the lead magazine article and garnered the cover (at left)!
In October 1974 while an undergraduate I did a consulting job for Barry Hirschowitz to design and construct some type of medical device.
I can't remember exactly what it was for, but think that it measured small skin voltages.
I might have been given schematics of a commercial device based on vacuum tubes that performed a similar function.
It was essentially a very high input impedance voltmeter, and drove a large analog meter
Replicating Digital Synthesizer
In 1975 fellow undergraduate student Eugene Mauro came to me with a proposal. Music synthesizers of the day were analog devices which created interesting but clearly artificial sounds. His idea was to use nascent computer technology to record and play back real musical instruments at different rates to produce a new kind of music synthesizer. He was a musician, and had taken some electrical engineering courses, but knew that he couldn't design it himself. Eugene's plan was to write up design details, build a prototype device, and obtain a patent for it. He paid me some money (I wouldn't do the work purely on speculation), and we were to share in the profits when they came rolling in. He had a patent attorney working with my writings, but the predictable happened: he ran out of money getting the legal work done. Let alone to have enough to actually build the prototype, which we estimated would cost thousands of dollars. The design was fairly large, consisting of multiple microprocessors (interesting that I selected the COSMAC processor for it) -- but I had (and still have) no doubt that we could have built it and that it would have worked. He had little choice but to abandon the project.
To this day, when I pass by the dozens of inexpensive Casio synthesizers in the electronics stores -- which are simply cheaper modern-day implementations of his Replicating Digital Synthesizer -- I cannot help but think of Eugene and lament that he never got any credit, let alone millions of dollars, for this. He had a music store in Waverly for a while. I ran into him maybe ten years later there where he had happily recently obtained some professional recording studio equipment.
Here are my description and design documents.
I designed an interface system for Maryland Electrical Testing (MET) which was delivered in September 1977. They were conducting an extensive powerline measurement study, I believe for the Army in Virginia. They had purchased many magnetic tape recorder units produced specifically to log AC voltage, current, and phase for that purpose: these recorders moved very slowly -- I think each tape cartridge lasted around a month. The recorder manufacturer also sold a reader device which would play the tapes back (at high speed) which connected in some way to a computer system for analysis. Which is exactly what MET needed. But it was extremely expensive. They thought "what's the difference between a tape recorder and a tape player?" The electronics! They figured they could modify one of the inexpensive recording units to instead play back the tapes. And they contracted this then grad student to design and build them the electronics for it (ostensibly for a lot less money than the commercially available reader).
This was an interesting project. The tape recorder had a capstan to keep the record speed fixed at a slow rate; on their modified unit they had removed the capstan. This let the tape cartridge spin as fast as the drive motor could spin -- which was quite fast, and moreover, not at a fixed speed as the tape wound from one side of the cartridge to the other. The record electronics was of course bypassed and my circuitry hooked directly to the tape track head coils.
I didn't really know what the signal level coming off of the head would be, but a measurement showed that it was in the microvolt range. Seemed kind of low (maybe in retrospect), but I designed the analog front end to amplify it a gazillion, used differential mode, and employed shielded wiring because that much amplification was sure to run into noise and pickup problems. It worked, but not as well as we'd prefer -- there were read errors after signal discrimination (NRZ decoding). One of their guys scratched his head and thought "Shouldn't the signal level be higher than we're seeing?" He looked a little more closely at the unit, and guess what he found? There was a permanent magnet hidden in front of the tape head to erase the tape! Made perfect sense, this box was sold as a recording device! But we were using it to play back the tapes, and every time we ran a cartridge through it, the tape was being erased more deeply (that might have been the big clue). I had so much signal gain in my circuitry that it was (partially successfully) reading the residual signal left behind after erasure. (Why couldn't the NSA use this same technique to read the erased 18.5 minutes of Nixon's Watergate tapes?) He removed the magnet and the signals were now in the millivolt range. I trivially reduced the gain in my front end, and presto, the tapes decoded perfectly reliably.
This project was a little after my MAXI micro endeavor, and I used some of the same techniques: 44-pin edge connector Radio Shack prototype wiring boards and card cage. I even used an Intel 8224 clock generator chip to drive the UART -- I knew it was overkill, and the 8224 ran notoriously hot -- but it certainly could do the task without a care on my part, and as a bonus it included the power-on reset circuit I also needed. This was not a microprocessor-based project, it was pure hardware. It had to pick up the signal and clock data off of the tape head, decode the NRZ pulses, and transfer the information to MET's PDP-11 minicomputer. I used a standard current loop serial interface to the PDP-11, but knew that the computer and interface would not be fast enough to collect individual pulse info. So I designed in hardware counters which the computer could poll periodically to retrieve the information. My undergraduate PDP-11 experience came in handy for this project even though I didn't really have to directly deal with that end of the system. After the magnet episode, it worked great without any problems. Almost as an afterthought, they wanted to be able to use the same device to input paper chart power data as well. They had constructed a tablet type of gizmo that let them put a printed chart on it and have a clerk meticulously move a stylus to various points on the graph; it was attached to a potentiometer. So my box had a mode to read the pot voltage with an analog-to-digital converter (ADC) and transfer the data to the PDP-11 whenever the operator pushed a sample button. Sounds crude, but this was 1977 and it did everything MET wanted.
Sometimes when you don't hear back from a customer after a while you wonder if equipment is even being used.
But I ran into them a number of years later, and learned that they used my MET-1 interface for quite some time. Nice to know!
Before specialized digital chips came out, it took a lot of circuitry to create the Pong video game:
Every mad scientist's lair must have a Jacob's Ladder:
I have a looseleaf binder filled with many other schematics I had designed. I just don't have the circuitry anymore, or can't quite remember what it was exactly for.
Maybe that's why I take it out on my students now, forcing them to write better documentation!
In 1981 the first DTMF decoder IC's had come out, so I designed this Message Converter as an entry in a contest:
When my wooden road sign deteriorated amidst occasional repair, I replaced it with a more modern version in October 2003:
I built a Theremin for my friend Larry Kruger as a birthday present in February 2005:
In February 2012, my friend Russ N3YI brought over a wire recorder that had been in his family since before he was born. Apparently these were predominant in the late 1940's and early 1950's; after that reel-to-reel tape recorders took over. His unit was a Webster-Chicago model 180. Here is some literature on it that was with the box. (I am amused at the drawing on page 4 of the lady in heels easily carrying the "portable" 27-pound unit. Compare that to a two pound MacBook Air!)
The unit had been passed down to him, and since he was a kid he had wondered what the recordings that were on the spools of wire sounded like. He had already had the AC power cord repaired, but nothing happened when it was turned on. I found the power fuse and it looked like it had disintegrated; so we replaced it and turned the power on. The tube filaments lit up -- after about 20-30 seconds, one of the plates was glowing red. Then the new fuse blew. I knew that the most likely failure mode for this type of gear not turned on in probably 50 or 60 years was the electrolytic filter capacitor. So I actually had slowly ramped the line voltage up with a variac rather than directly powering from 120VAC. I'm guessing that replacing that cap will restore the box to operational order, but didn't bother with that. Our goal was simply to retrieve the audio recordings for Russ (at right).
I pulled all of the tubes to prevent the (again replaced) fuse from blowing. The good news was that the motor (there is only one) worked. After some cleaning with alcohol and judicious lubrication I could make it go forward to play and reverse to rewind. It still took some finger action on the mechanism to get it going in either direction. The rubber mountings had deteriorated and in some cases turned to dust. The wire broke a few times in the process of getting the mechanism to do its job. It's kind of interesting that there is a mechanical part which moves the head up and down as the wire winds onto either the supply or takeup spool. This evenly spreads the wire onto the spool much like a sewing machine, and prevents bunching. I also thought it interesting that there is no capstan -- which on reel-to-reel and cassette decks keeps the tape velocity constant as the diameter of the takeup reel increases throughout the play time. This design simply used a large diameter takeup spool, so even when it is filled from the supply spool its diameter isn't much greater than at the start. The motor speed and idle wheel reductions set the transport speed.
With the tubes removed, we had no active electronics. But we didn't need no stinkin' tubes! I attached the leads from the head to the input of a (transistorized) audio amplifier (in between the two laptops in the picture below). We threaded the wire through the (playback in this mode) head and the takeup reel and got the wire moving. We could hear the audio from the past emanating from the amp's speaker! The rest would be a cakewalk.
I tried feeding the head signal directly to the microphone input on the laptop, but there wasn't sufficient gain. So I connected the head to the input of the transistor amplifier and the amp's output speaker jack to the laptop's line-in jack. With Audacity I could record the session and edit it afterwards. There were sections of the wire ("tape") that had great audio levels and others that were much lower. Some were simply people talking too far away from the microphone, but on other sections I think that someone pushed the record button over top of the previous recording and mostly erased the former data. I selectively edited portions and amplified them (a lot) to try to bring the sound up to a listenable level. Of course that boosts the noise level quite high. Another problem is that I live too close to WCAO-AM (they moved their transmission towers to the neighborhood after I moved in!). So in the sections of the recordings where I amplified it a lot there is a residual background of the local radio station. Oh, well.
In the end, I made up audio CD's and MP3's for Russ of five recordings: Sondra's sweet 16 birthday party (his Mom); Rosie's birthday party from February 29, 1952 (Russ' great-grandmother whom he is named for); the Kaufmans' 25th anniversary party (Russ' grandparents); a recording off of Philadelphia's WPGM fm radio station (I think those are the call letters, it is a bit hard to clearly make out); and a sales pitch from Slenderella (the voice is a British woman which makes more sense when I see that the company is in the U.K.). Here is that last recording. Here are all of the recordings. You will need to get the unzip password from for those.
It was a fun little project which reminded me of the vacuum tube days and the more formal manner people behaved in radio-like interviews in the 1950's.
I had noticed some detritus in the trunk of my 1995 Infiniti. Further inspection revealed that the rear speakers had deteriorated -- the cones were now isolated from the frame, suspended solely by the voicecoils. Recalling how easy it was to replace speakers in 1970's era cars, I looked to swap them out. But I couldn't figure out how to remove them! They were clearly bolted in from above but there were no screws on top to remove the grills in order to access the speaker mounting screws. I concluded that it would be necessary to actually remove the rear deck below the back window. This seemed drastically crazy, but a web search provided instructions (which didn't turn out to be precisely correct) indicating that I wasn't crazy, that deck indeed had to be removed. Didn't want to leave the car disassembled too long, so I bought replacement speakers before removing the originals and attacking the job. These are two-ohm units, and most of the ones available are four-ohms. Ironically, I found and purchased a pair of Infinity speakers for my Infiniti car. It was a bit of a job removing the top deck, but it all worked out. Got this done in March 2012 and now the bass response has returned. I guess these speakers will last the remaining lifetime of the car.
With the speaker problem fixed, I wanted to address an issue that had been gnawing at me for a while: playing MP3's in the car. At first I had tried a Belkin FM transmitter to let an MP3 player broadcast to the car radio. It appeared to have a very low output power, because no matter what frequency I selected it seemed to heterodyne with broadcast stations as I traveled. It was too aggravating. Plus I was using the cigarette lighter socket to power it and it was more cumbersome than I'd prefer to hookup and disconnect.
I had settled on using a standalone audio amplifier (abandoning the car radio altogether) -- the same one shown above in the Wire Recorder episode. Powered also through the cigarette lighter socket, it worked okay. But it still was a cumbersome connection and of course the sound was not nearly as loud as the car radio would be.
I was determined to establish a direct connection between the MP3 player and the radio's internal audio amplifier. After figuring out how to remove the surrounding dashboard cover (that houses the four accessory switches at the top of the photo) it wasn't too hard to remove the radio itself. I took the top and bottom coverplates off of the radio. Still thinking with a 70's attitude, for some reason I expected to see a stereo volume control potentiometer which would have been trivial to interrupt to divert the audio input to an external jack. But of course I knew that this radio was all digital -- the volume control is an optical encoder that drives a microcontroller. As an integrated unit I wasn't sure how I could find a place to cut the audio path. I was stymied trying to remove the circuit boards anyway: I didn't readily see how to release them (without a service book); I was afraid that I would pry something that wasn't intended to be pried and break a perfectly good radio.
There were two unused connectors on the rear of the radio. I recalled that this model had an option for a separate CD changer unit that mounts below the heating/cooling control section. There is a button on the radio to select this sound source (which did nothing at all without the changer installed). I became obsessed with using this audio path for an external MP3 player. Clearly this is the preferred method: all I should have to do is convince the radio that an external jack is a CD changer. I could connect a stereo audio input jack to the radio connectors and be done! I failed to get any specifications on the radio interface, even with the exact model number, so I attempted to reverse engineer it. How hard could that be? The radio connected to the car wiring through two plugs which were more complicated than the older simpler ones I was familiar with (power, ground, left/right speakers). I figured it would be easier to work with it in the car instead of running it on the workbench. So I made up a cable to connect to a DIN and some other type of jack on the radio, re-installed the radio and probed the signal lines with my VOM (actually DVM). There has to be a way that the external changer tells the radio that it's there. I guessed that it might ground one of those pins, so I carefully grounded each (through a resistor in case I was wrong). Pushing the radio button each time still did nothing. So I guessed that maybe a pin needed +12v instead of a ground for that purpose. Still nothing. Then thought that maybe the micro sampled those sigs on powerup; so I tried the ground and +12 on each pin (13 of them) powering down/up. Still nothing. I dragged an oscilloscope to the garage and looked at each pin while activating the radio button, looking for a pulse or something. Nada. I put a signal generator onto each pin (through an isolating cap) and found that I could drive the left and right audio paths (superimposed on the radio or CD playing). But the MP3 player's audio output on those same pins accomplished nothing -- the sig gen must have been overpowering internal circuitry. Anyway I still had the other audio source running. It killed me, but after spending a couple of days on this I had to admit defeat. I know this is the way to go, but without the radio or changer specs I could not make use of this method!!!
Back to Plan A (interrupt the audio path inside the radio somewhere and attach an external jack). Pulled the radio out and removed the covers. After about a half an hour or so I managed to remove an auxiliary board which houses the balance, fader, bass, and treble controls. The audio path has to go through here, right? Failed to identify any discernable signals. After about another half an hour or so I manage to remove the main circuit board. I was a bit terrified with this: there are a couple of flat cable connectors, I was flying blind, and feared I would break something or not be able to re-assemble properly. This radio has a bulit-in CD player (one disc as opposed to the 6-disc external changer) and I thought that there would be a separate CD player circuit board which had to attach to the main board. There just had to be a stereo audio path between the two! My guess was correct: there was a flat cable between the two boards with about 15 or 16 lines. By this time I had gotten the radio operating on the workbench. My plan was to interrupt the CD audio path, so I would have to play a CD while listening to MP3's. I put the boards back into the radio and good news, it still functioned. But now I had to find the left and right audio pins on the interconnecting flat cable. To get to the board pins the radio had to be upside down while playing a CD: it made a scraping sound but mostly managed to play with the anti-gravity positioning. Tadah! Found the two audio paths. Next job is to interrupt them. Removed the board again. It is a combined surface mount/through hole configuration. After some work I identified two traces I could cut to accomplish the task. With a 4-conductor + ground shield cable I routed the two audio paths through the cable to a standard stereo miniature jack with internal normally closed contacts. Routing the CD-audio through the cable/jack was not as ideal as the failed Plan B (CD changer one-way audio input) but should work fine. Reassemble everything, try with MP3 player, and it all works great! Lucky for me the audio levels were compatible as is.
It would be nice if the MP3 player's internal battery charge level were not an issue in the car. On a roll, I wanted to put a charging jack near the car radio. So I put in a 5 volt linear regulator and attached its output to a standard USB socket. I mounted it directly above the cigarette lighter but for the life of me I couldn't get to its wiring to power the regulator! Just bridged a wire onto the +12v pin on the radio connector to feed it. I could now use a standard USB cable to the MP3 player to charge it. (Two days later in the dollar store I saw a dual USB converter that plugs into the cigarette lighter socket that accomplishes the same thing -- but it is bulky and awkward compared to the jack I installed.) As a finishing touch, I made up a 6" USB cable and a 12" audio patch cable to avoid a bunch of unnecessary cabling in the cramped space.
The final configuration is in the photo above. The external audio input jack and USB charging socket are just above the cigarette lighter. To play a CD I just have to unplug the audio cable from the external input jack. While I had the dashboard open I added a small piece of angle stock (painted black) to the bottom of the tray where I usually put the empty CD case for the loaded disc -- occasionally it would fall out when accelerating (nice after 17 years).
One MP3 player I have will charge while it plays if the two USB data lines are shorted to ground; another one won't charge unless the data lines are open! (it still doesn't display that it is charging, but it is). So I added a
All content Copyright 2013 IC Engineering, Inc. This webpage last updated: January 25, 2013