brainwagon

Eldon, WA0UWH was inspired by my recent experiment with Tatsuo Kogawa’s micro transmitter, and decided to build his own. Unlike my rather crude (but surprisingly effective) lashup on some copper clad board, Eldon designed a tiny 0.5″x0.8″ board, etched it and used surface mount components to finish it. Very nifty, and totally dwarfed by the […]

Yesterday’s video showed a very fussy version of Tetsuo Kogawa’s 1 transistor FM transmitter, which worked after a fashion, but which seemed really squirrely. Almost any motion of anything caused the circuit to behave rather badly as capacitance changed, and I picked up a considerable amount of hum. Today, I rebuilt the circuit onto a […]

Tetsuo Kogawa’s circuit is pretty well documented, but not in conventional schematic form. I decided to enter it into LTSpice to see what it could make of it, and decided to go ahead and put the schematic online here, with perhaps a few comments: I’ve set this up more or less as I built the […]

A couple of days ago, I mentioned Tetsuo Kogawa’s MicroFM transmitter, a simple one transistor FM radio transmitter. Tonight, I decided to put it together on an experimenter’s breadboard. I didn’t have the 2SC2001 transistor that Tetsuo Kogawa used, so I just dusted off one of my $.10 2N3904 transistors, and dug the rest of […]

In digging around for small AM radio schematics (I’m more interested in AM than FM), I ran across Tetsuo Kogawa’s site on building the “simplest” FM transmitter. It’s actually pretty cute, and has just a single transistor, a few resistors and caps, and a coil that you can wind yourself on the threads of a […]

Like many mechanical skills, soldering may seem fairly daunting if you’ve never done it before, but it’s really not that hard. If you need a basic getting-started guide, you could try out the new Soldering is Easy comic book. I think the only thing it really could use is a better guide to buying a […]

I’ve been interested in LOWFER radio (low frequency radio operation) for quite some time. Under Part 15, unlicensed experimenters can transmit signals in the frequency band between 160khz and 190khz, subject to certain regulations on power and antennas. You can read more about it here. I was bored the other day, so I decided to […]

In thinking about the 555 timer AM transmitter that I constructed last night and trying to understand how it might work, I eventually ended up with a basic question about PWM modulation. It boiled down to this: if you are generating a pulse width modulation signal with a rate of (say 540khz) but pulses whose […]

I mostly avoided the siren song of the 555 timer that seemed to echo through the blogiverse during the recent 555 contest, but when I was out and about last weekend, I picked up 10 of them from Anchor Electronics, and they have been taunting me from the shelf ever since. So, last night I […]

Over sushi this evening, Tom mentioned “Chua’s circuit”, or “Chua’s oscillator”. I knew that I had seen this somewhere before, but failed to remember that Chua was also the guy who first theorized about the memrister: a circuit element whose resistance is proportional to the sum of the charges that has been passed through it. […]

I’ll just lead off with a picture: This is a graph of the so-called “Lorenz attractor”, first described by mathematician Edward Lorenz in his paper Deterministic Nonperiodic Flow back in 1962. I learned about this kind of stuff probably back in highschool by reading Scientific American. Anyway, the equations themselves are pretty simple, but describe […]

A bit more digging on yesterday’s topic (crystal microphones) yielded this book, published by the U.S. Army, entitled CW and AM transmitters and receivers which included some additional useful information regarding the construction of crystal microphones.

I’ve been pondering a couple of projects that could benefit from having custom PCBs manufactured, and David Jones twittered about one I hadn’t seen before: Open PCB Prices seem very good, and you can also order some pre-designed open source boards for very modest prices. I’ll check it out more later.

Well, the other I2C based breakout board I got from Sparkfun was for a Microchip MCP4725 DAC. It’s a 12 bit device, and will eventually do duty controlling the voltage controlled oscillator in my beacon transmitter. For tonight though, I just wanted to make sure I could program it, so I soldered on some header […]

In considering the long term accuracy of the RTC chip that I was playing around with, I did some additional thinking and reading. My understanding is the error comes from the accuracy of the crystal oscillator: the 32.768Khz timing crystal probably has an accuracy of 20ppm or even larger. My guess is that this is […]