ElectronicsNerd.com

Welcome to ElectronicsNerd.net where you will find a collection of personal projects involving electronics and my other fun hobbies like photography, gadget hacking, and music writing. I live in Akron, Ohio, and I'm always willing to chat about cool projects, maybe get something going with other people. So if you see something you like, send me an email or something.

When I was a kid, movies like WarGames, E.T., Weird Science, Real Genius, Cloak & Dagger, D.A.R.Y.L., and a bunch of others got me interested in making cool stuff with science. If you want a great modern-day movie, I don't think Primer can be beat. After all, it was made for $7000. Hot-diggety. A genuine science-is-cool movie whose creepy aura takes a long time to shake off.


September 1, 2010. RF projects

Direct Conversion Shortwave Receiver with Broadband RF Amplifier - 3-10MHz

Who says you can't build radio frequency projects on a breadboard? Well everybody, actually. Capacitance, or charge potential as I think about it now after messing around with all this, plays a major role in the tuning of radio circuits. In conjunction with inductance, capacitance determines the frequency of an LC tank circuit. The body carries charge, so when you reach out near the circuit, you add capacitance to a tuned circuit, thereby changing the tuning. So just like the famous Theremin, the radio drifts up and down in tuning.

But all that aside, I have acquired a number of really snazzy ICs and coils, and I didn't want to commit any of them to finished projects until I had experimented a great deal with configurations and layouts. These days, they are rather scarce, as digital techniques like frequency synthesis have made the old methods go the way of the dodo. Not as pretty as the passenger pigeon, but still.

So above you see a direct conversion shortwave receiver adapted from the Ramsey Electronics kit schematic, with an added wideband 3-30MHz preamplifier. The schematic for the preamp was taken from Joe Carr's book: "Mastering Radio Frequency Circuits." Any of Joe Carr's books are excellent for the radio homebrewer, and I had to renew his books from the library here in Akron three times before I began to understand any of this stuff!

As shown, I am able to tune from 3-10MHz, and then I have to swap the coils on the front end and local oscillator to change frequencies. With this setup and a 100' antenna out my window, I received CHU from Canada (a time standard), programming from Cuba, China, Russia, Africa, and numerous ham radio conversations. I also got automated weather conditions for the east coast of the USA, and the weird beeps and boops of telemetry and fax transmissions.

Because the local oscillator itself determines the tuning of the receiver, a slight offset allows reception of SSB and CW. Going dead-on with the frequency, ordinary DSB AM stations are received, with the added benefit that a frequency counter tapping the local oscillator will read out the exact frequency to which the receiver is tuned. A superheterodyne would mix the incoming RF from the antenna with a local oscillator to produce an Intermediate Frequency, making direct readout impossible without an offset capability in the counter.

Does all this sound like mush? I have been away for a while, and this is what I've been doing. I made so many of these radios before I decided to buy a Grundig G3, and now I can take my sweet radio anywhere without attracting unwanted attention.


Monaural FM Transmitter
I sure wasn't going to restrict myself to AM. Here's an amazing three-transistor circuit that broadcasts whispers to an FM radio in the house. This design is awesome. What makes it so special is the buffer transistor before the antenna; the output stage doesn't load down the preceding electronics. The circuit can be found at www.talkingelectronics.com, run by an incredible Australian named Colin Mitchell.

It's horrifying how well this circuit works. I was half expecting the spooky van to pull up in front so I really didn't use it much. In time I'll post some more circuits. I mostly concentrated on receivers, because it was a magical experience building circuits out of a handful of parts that brought the world inside. You don't need an expensive commercially-made product to participate in radio communications.

One final note. Yesterday I visited Akron Antique Audio and was given a tour by the proprietor. If you want to see some awesome old radios, stop in and check the place out. I picked up a couple of 10.7MHz IF transformers, the same kind I used in the shortwave radio above. Get on it, because he'll be retiring soon.


July 19, 2010. Radio is Witchcraft.

I have been working on radio receivers and transmitters, and boy do I have to tell you this is amazing. I guess the barrier to entry for me was not owning an L/C meter, which I now have had for a month. I was very uncomfortable not knowing what inductors did or how they were measured. Now that I have one, I still don't know what they do. But seriously...

The coolest thing ever was creating a shortwave radio receiver from component parts. Suddenly, I was part of a community of speakers and listeners across the globe. Of course I checked out commercial offerings in shortwave radios, and there are a lot of features that I can't really duplicate, but I don't mind fiddling with dials. So my current "radio" is about 25 components on a breadboard. My antenna is a long wire out the window. I can't afford to buy a good radio, and I definitely can't afford to buy a cheap one, considering what I've gotten with nothing at all!

Let me get my stuff together and I'll soon show you what I've found: the good, the bad, the elegant. I've built around 20 radio receivers and transmitters, and I've learned a whole lot by doing. Maybe I'm destined to be a ham after all. I was part of the CB craze, thanks to Dad, but those who are involved with Ham radio seem to have a larger investment in the technology of the craft, at many different levels.

That's all for tonight; I have some more dial twisting to do. I've heard Croatian, German, French, Spanish, and Russian. I now love AM radio, but I also love SSB, now that I know what to do with it. These broadcasts also sound nothing like commercial radio here in the United States. There is lilting music from Cuba, a lonely church organ somewhere in the Ukraine, and voices that teach, inform, and entertain. I have yet to hear an itch cream or auto parts commercial on the bands outside commercial radio.

This is electronicsnerd, thank you for watching. Bon appetit. :)


July 4, 2010. Automatic Closet Light: a power MOSFET for your home.

Here again, a circuit answers a specific need. A tall, skinny, dark hall closet was in need of some illumination - and apparently a semiconductor. I had purchased a $9 garden light set that had four powerful LED pairs and a beautiful solar panel. Since four deep shelves needed light, I figured I would mount the LED fixtures and install a roller-type switch so that when the door shut, the lights would go out. I put the solar panel aside for some other cool project in the future and harvested some other neat components that comprised this set: long wires that terminated in DC barrel jacks, double-ended DC plugs on long wires, plastic covers for the jacks, a battery case, an SMD charging circuit. This was truly a lot of stuff for what I paid for it. I did end up throwing away the cast spikes that were meant to be stuck in the ground outside. There truly was no place I could set them without being poked.

At 12V with suitable resistors for each LED leg, the circuit drew 80mA, and I could have called it a day. What disturbed me was that the resulting presentation was that of a refrigerator light appearing to be on all the time. What I wanted was an indication to the user that Magic was taking place, so I enlisted an IRF510 power MOSFET and a small electrolytic capacitor.

When the switch is engaged, the .47uF begins to charge through the 4.7 Megohm resistor. A small amount of current is withdrawn by the 4.7 Meg leading to ground, but that part has its place later. The capacitor is still able to charge up to the triggering voltage of the MOSFET, and the drain-to-gate channel is opened, producing a nice fadeup for all the LEDs. When the closet door is closed, the capacitor still has charge, so the light stays on momentarily, until that charge is drained away by the second 4.7 Meg resistor to ground.

These values can easily be monkeyed with, and I did a fair bit of monkeying. A larger value for either the charging/discharge resistor or the electrolytic will produce a longer fade time, but in this case the time was determined by "feel." The most important thing was the user interface, and so I decided to work with the values until I had achieved the Magic. Of course, the time could have been calculated by R times C, with the goal being the triggering voltage of the MOSFET, but I enjoy plugging components into breadboards more than I do scratching pencil on paper.

The result is a circuit that has been all but forgotten, drawing no current while dormant, waiting to play back its simple light show when the next person opens the door.

April 10, 2010. Here's my schematic for a Sony remote-controlled audio volume using a pair of AD5220s. As they don't like to be fed voltages outside of their operating range (0-VCC) I added a 100K resistor to each input so that the audio can float between the 100K fixed resistor and the 100K digital potentiometer.

After figuring out what the remote's heretofore useless volume controls were sending, I had the PIC look for one of two button codes. Both digital pots then increment or decrement, giving across-the-room controllability to my speakers. I've posted the PicBasic Pro code in the Downloads section, but this was a project that was highly dependent on my individual Sony remote. The bits of code shrapnel that are commented out show how I initially discovered the remote codes using a serial LCD. When I pressed any of the remote buttons, the button's code appeared several times on the LCD.

At this point, it's an in-line design, but it's easy enough to replace an existing volume control knob. I just wanted the flexibility of still being able to use said knob when I wanted to. Otherwise, leaving it in the middle of its range gives fine results.

This shouldn't be used in a critical "performance" audio situation. When the buttons are pressed, sweeping the digital pots through their range, there is audible zipper noise during the changes. Brrrripppp.... Apparently there are some zero-crossing detection schemes that can eliminate this, but I'm happy enough to control audio levels from my couch now.