I am a loving father of two beautiful daughters and a loving boyfiend of the kindest, sweetest woman I have ever met. I am also a seasoned and experienced family law attorney. I am fairly handy with a soldering iron, with bicycle repair tools, and with wood glue applied to balsa wood and paper.
As my friends and family already know, I am a man of many hobby passions. I can't say I am a master of any of my hobbies, but they do provide a great deal of pleasure for me. Here are some of the geeky hobbies that hold my attention far longer than they should.
Geeky Hobby Number 1: Do-it-yourself Electronic Circuits.
Yep. I like the smell of melting lead and tin in the morning. ;-) Why spend $15.00 on a store-bought radio or audio amplifier when you can spend hundreds of dollars on tools and parts and then spend countless hours hunkered down over a magnifying light soldering the pieces together and making your own radio or audio amplifier? Because it's MORE FUN. When you test a cicuit you built yourself, and it actually works the way you intended it to work, well there are only a few things more satisfying than that, let me tell you.
Geeky Hobby Number 2: Model Rocketry.
I am a "BAR" (born-again rocketeer). In the 1970's, as a child, I learned to love the space age hobby of model rocketry. My buddies and I built Estes and Centuri rockets. We launched them from the local junior high school athletic field. Some of them even came back.
Geeky Hobby Number 3: Railroads and All things Train-like.
My paternal grandfather was a locomotive engineer for the Norfolk & Western Railway. He made many trips driving steam-powered locomotives through the town where I was born (Petersburg, VA). Another ancestor, on my mother's side of the family, was also a locomotive engineer. I guess you could say I have railroading in my blood. I love seeing locomotives, and the trains they haul, in action.
To honor my railroad heritage, and my love of railroading, the background image for this web page is Norfolk & Western K-2a class steam locomotive number 128. This is a 4-8-2 wheel arrangement locomotive that was originally made in the early 1920's. The K-2a locomotives were later streamlined, as you see here, and became very handsome. This picture shows number 128, eastbound, at the station in Roanoke, Virginia, on May 5, 1957. The original picture can be found here.
Here is another N&W K-2 class locomotive, number 125, without streamlining.
More information about the N&W K class locos can be found here.
555 Timer IC Astable Mode Calculator: Calculate the Value of R2
To calculate the value of R2, enter the value of R1, the value of the capacitor, and the desired output frequency:
Note: Enter only numbers (and a decimal point, if needed). Do not leave any of the user input fields blank.
The value of R2 is:
The time high (on or "mark") is:
microseconds (millionths of a second).
The time low (off or "space") is:
microseconds (millionths of a second).
The duty cycle (time high as a percentage of the total time (time high plus time low)) is:
Building the Circuit with the Closest Standard Value Resistor
The E12 series standard value resistor closest to the value of R2 is:
If you build the circuit using the E12 standard value for R2, the output frequency of the 555 IC will be:
Your desired output frequency is .
The difference between the actual output frequency, and the desired output frequency, is:
Note: A positive value in this box indicates that the actual output frequency is HIGHER than the desired output frequency. A negative value in this box indicates that the acutal output frequency is LOWER than the desired output frequency.
Practical Output Frequency Limits of the 555 Timer IC
When you are using the high power (200 mA) version of the 555 timer IC (sometimes know as the "TTL" version, not the "CMOS" version), you are limited to a frequency output of about 100,000 Hertz. Some circuit builders can get a reliable, higher output frequency, but the original datasheet says that 100,000 Hertz is the upper limit.
As you can see by playing with the value of the capacitor using this calculator, to get a high output frequency of over, say, 20,000 Hertz, you need to reduce the value of the capacitor to a fairly small value, such as .001 uF or lower. To get a high-quality capacitor with a fairly tight tolerance at these lower values, you may need to use an expensive, bulky, plastic film capacitor. That may not be practical.
Also, as the output frequency increases, the duty cycle also increases. The duty cycle is the percentage of time the output stays in the high or "on" state for each cycle of the square wave. At duty cycles in the 70 to 99 percent range, a lot of power is consumed. Most designers of 555 astable circuits like to design for a duty cycle as close to 50 percent as possible. To achieve this (without adding diodes or transistors to the circuit), the value of R2 has to be much larger than the value of R1. A ratio of about 10 to 1 (R2 to R1) is a good rule of thumb. Practically, however, you cannot reduce the value of R1 much below 1,000 ohms (for stability and power consumption reasons). BUT! There is always a "but". But, if you make the value of R2 very large compared to R1, then the value of the capacitor has to go DOWN if you want a very high output frequency. So, it's a balancing act. Like most things in life. :-)
- Brock R. Wood (firstname.lastname@example.org)
More Geeky Hobby Information to Come.
As I have time I will update this page with more information on my geeky hobbies.