Thursday, May 26, 2011

$5 Radio... RETURNS!

Everyone remembers my $5 radio! If not, rather than adding on to that entry from almost two years ago:


Any way, I have been thinking almost since I built that power supply that it is too bulky. At first it was kind of neat to show off, it looked original and unique, but it's hard to put it behind a shelf or on a desk (the reason I bought the radio in the first place is because it would go well as a shelf for a flat panel monitor) and it was cumbersome or impossible to deal with. I thought about encasing the power supply in Plexiglas but this would be expensive and, frankly, more work than I think it's worth.

So! I took apart the radio to see what was inside. Oddly enough I hadn't done this yet. My original idea was that I could use the power button on a relay of some sort to make sure the transformer, wherever I decided I wanted it to go during this rebuild, wouldn't be energized all the time. I still have to pay the electric bills!

There was a lot of space inside the radio! AND when I cut through the wires on the switch I found out a few interesting things. The first was this was simply a switch: open or closed. Easy to work with. The second was that the radio uses 28V AC as logic, at least for turning itself on and off. I don't think the switch handled all of the power, just simply told the radio when to look like it was turning on, which I am only guessing at based on the fact that the radio has memory buttons and no internal battery. It would need some sort of power all the time (in a standby mode or similar).

I decided to make it extremely simple. I ran 120VAC in to the switch, then back out of the radio about four feet to the primary side of the transformer (and I attached the neutral here as well). The extra wiring means the switch controls the transformer, and no energy is wasted in hysteresis and core losses in the transformer when the radio is off. Then I ran (existing) wire from the secondary of the transformer inside the radio. From there I implemented my original voltage divider scheme, only instead of the resistors screwed in to a wooden plank they are JB Welded to the underside of the plastic case and soldered together. This is a much better construction: the JB Weld will hold better and will insulate the plastic from heat transfer (theoretically) and the solder joints are much lower resistance than what previously existed. I also eliminated one switch while keeping the same functionality, and there's no sketchy "HOT!" labeling to scare off the Safety folk if I were to HYPOTHETICALLY use this radio in my office at work...

When it's all back together, the transformer sits comfortably far away from the radio, and the radio looks like it was meant to be there! This is also a perk because I currently have a disassembled satellite dish, unfinished amplifier, and a random microcontroller project going on in the same area. Feel less cluttered and/or nerdy! Well, it's the best I can do. The only thing that I am not sure about is whether or not the switch can handle 120VAC. There was nothing on the switch indicating it could or could not, so I decided to take a chance. We'll see how it goes!

OH! I also added a fuse. Just in case. You never know.

Sunday, May 15, 2011

Suspension explosion!

So I tested my suspension lift about a month ago on a little patch of mud in Manchester, TN. It was rainy, and I drove off the road and the first bump I hit I hear what sounds like a shotgun going off under my truck, followed by the truck rapidly sagging towards the front driver's side. OH NO! I apparently didn't seat the torsion bar in its rear mount all the way, and it stripped the splines partially out.

The bar is supposed to sit about an inch and a quarter into this mount, but I didn't check it before bolting everything back, and the bar was only sitting about a quarter inch in the mount. This is just fine for normal road driving but as soon as I hit a good-sized rut off road, POW. Batman sound effects all over the truck! Long story short, I limped the truck to a local school parking lot and was able to beat the suspension back together with a really big hammer (my favorite tool) well enough to get home.

This is a picture of the torsion bar, the old (dirty) rear mount for it, and the new (shiny) mount with fresh splines. This mistake set me back $70 at the dealer BUT if off-roading isn't breaking the occasional part on the truck, I must not be doing it right. Speaking of which, after I fixed the problem I went off road at a wildlife management area about two weeks ago and ripped my front bumper, due to Nissan giving the Frontiers a HORRIBLE front approach angle. So I went ahead and ordered one of these:

Winch Bumper/Bull Bar

Should be very fun. Improves approach angle, has a winch mounting location, and will most likely destroy anything I hit with it, instead of the current setup of anything I hit destroying my bumper. Any way, lessons learned: Always hit the torsion bar mounts with a hammer to make sure they're fully seated on the bar before cranking them back up. Yay!

Truck power! Also noteworthy, on the next outing (in between destroying the bumper and having the suspension explode) the 102" whip antenna I have for my CB ripped out of its mount. Apparently removing it any time I go inside a shop, my garage, or a parking deck was not that great for it, so I replaced the mount and then built something to tie the antenna down, kind of like Army vehicles do with their antennas when they're traveling on the interstate.

Solutions! Always helpful. Although the antenna is not very effective when it's bent over, it makes maneuvering in anything other than under clear blue sky. And it's easier on the mount for not having to remove the antenna all the time.

Stereo [Audio] Amplifier (from scratch)

I have this old set of speakers that are in an older post, where I rigged them up to an old head unit from a car. This setup works fine but I think I can do better by constructing my own amplifier specially built for those speakers. My goal has been to get 30 watts per channel, and to build everything from generic electronics parts.

I decided to start small first, since I have never built an amplifier like this. I have built current amplifiers to drive motors, but the low noise, high gain requirements of audio along with spending WAY too much time doing transistor biasing and impedance matching make this job a little bit more of a challenge. Any way, my first design naturally was an LM741 style operational amplifier set up with some negative feedback (the small resistor) to keep the signal from running away and making the sound quality very, very bad.

This was a very simple design, and delivered MAYBE a quarter watt to a speaker. The sound quality was terrible but it was a proof-of-concept type design at this point.

This was my whole setup, with my MP3 player (see previous posts about THAT), breadboard, speaker, and the power supply I built a few months ago (also in a previous post). The next step I felt was to get away from integrated circuits and switch to discrete transistors to drive the speaker.

This was my second design. There were some other changes besides switching from an op-amp to discrete 3904, TIP-42 and TIP-31 transistors. The first of which was that I found a little transformer in a box and used it to make a 12V unregulated power supply so I could actually move it around. The second change is that this design actually sounds really good. The simplicity of the amp keeps the sound from getting distorted or over-manipulated (possibly a placebo effect) and I used it for a few weeks to listen to music on the porch. This design delivers about 2W to the same speaker.

I am currently working on the next step which is a 30-watt stereo amp. The previous designs have been mono but when I get the first channel working at 30 watts I will go ahead with building a second channel. Currently the amplifier is in design stage where I am working out some bug which is causing all of my fuses to blow as soon as power is applied. I have completed and soldered together a specially-built 40V power supply for this part, and I have let the smoke out of two transistors that were in my power supply so far, so hopefully that stops. More to come! This has been a long project.

Also I came across something I found to be pretty hilarious while I was at work. Maybe others will also see the humor in it:

Tuesday, May 3, 2011

Fridge Speakers update

I thought I might fix my iPod (the one that only works when it's cold) so I can sell it for some extra pocket change, and also have the challenge of how to get music back in the fridge some other more interesting way (such as through the power lines). I thought the problem was with the headphone jack and the various devices that control it, but I bought a $4 replacement from Hong Kong and it still operates the same: only when it's cold. So that was $4 to figure out where the problem wasn't, which I guess isn't a total loss.

In other news, I have figured out a great power-saving scheme for my desktop computer. I had been leaving it on 100% of the time in case I needed to download a file from it remotely. Then I discovered a protocol called "Wake on LAN" that allows the computer to be woken up from suspend or hibernate by sending its network card a "magic packet". So now my computer is set to suspend after 1 hour of inactivity AND spin down the hard disks, and I can wake it by sending the magic packet from my phone using a Droid app called WoL. I expect this will be useful one day in the future when I have to pay my own power bill. Until then I have hopefully just increased the life of my computer.

Also I wanted to upload a picture for fun.