Nuts & Volts - April 2007

>>>READER-TO-READER QUESTIONS AND ANSWERS

many examples. After the manufacturer's published literature, some people consider this book to be the definitive resource.

And finally, if you get stuck, there are a variety of online resources for you to ask specific questions. Microchip has their own online forums and you should also check out the MIT PICList email list at www.piclist.com.

Aaron Garber Arcanum, OH

#3 Start with a simple microcomputer like the PIC with only 33 instructions to learn.

You might start out with a microcomputer simulator. It is a piece of software that runs on your PC and looks like a micro. There is a window where you write code; “move A,B” and other windows where you see the number move from B to A or A to B, as you will soon know. Microchip MPLAB is free; a number of companies give away their development software.

If you want to go straight to hardware, search for the BASIC Stamp (as there are many competitors). You write in Basic (some allow assembly), but you have a tiny computer up and

working in minutes. There are hundreds of examples of working code and good help forums.

Go to any microcomputer website. MicroChip, TI, Zilog, Silicon Labs, Atmel, etc., and look for development boards. You need a board with a microcomputer, LEDs, buttons, and places to add more parts. I have SiLabs C8051F005 development kit that comes with a good simulator/compiler. SiLabs and TI have boards as small as your thumb. Mikroe.com has beautiful large boards. Good luck!

Ron Simpson Loveland, CO

#4 Programming is a large topic, so the answer will be a bit general. Here is a quick run-down of the basics and places to look.

The most important thing to know is that learning a language is only a small part of programming. Understanding algorithms, data structures (how to store and access data), and overall design are extremely important when writing programs with more than a few hundred lines of code. I'd recommend getting a book on data structures and another on software engineering (that's the fancy

term for planning and managing program development).

As for the actual languages to learn, programming for computers is rarely done in assembler these days, unless you are working on device drivers or performance-critical applications. In general, high-level languages such as C, C++, C#, Java, and Visual Basic are much more prevalent. There are numerous books dedicated to each of these languages and they cover them in lots of detail. There is still a lot of value in learning assembler, however, as it gives you a better understanding of how the computer really works. One of the best books on computer assembly programming is "The Art of Assembly Language Programming" by Randall Hyde. It covers the Intel x86 assembly language and covers many of the underlying concepts needed for successfully writing programs in assembler.

If you are more interested in programming microcontrollers, there are fewer languages to learn. Many microcontrollers can be programmed using high-level languages such as C or BASIC. This makes programming these devices much easier and also makes the source code much easier to understand after the program has

supply only enough current to maintain the voltage at 6. 8 volts. Using an LED as the voltage reference provides some temperature compensation. To adjust the pot, connect a fully charged battery and adjust for 6. 8 volts at the battery. If the battery is not fully charged, set the pot at its lowest (toward R4) and check periodically until the voltage rises above 6. 8, then back off to 6. 8 volts.

The TIP41 will get hot charging a dead battery, so a heatsink is advised. Mouser part number 532-6237B will probably work. TIP41A, B, and C are also okay to use. Mouser has no minimum order ( www.mouser.com).

Russell Kincaid

Milford, NH

#3 A simple solution would be to use a handful of rec-tifing diodes, capable of handling the current of the battery charger. Connect the diodes in series to get a 5. 5 to 6 volt drop and connect them in series with the six volt battery.

Lance Corey Fullerton, CA

#4 A battery maintance or float charger just replaces the charge lost due to internal leakage. A resistor can be placed in series with the output of a 12V maintenance charger for use on a 6V battery. If the battery is rated at 24 amp-hours

and is dead in 30 days (720 hours), it must be losing charge at a 33 milliamp rate. To drop 6V at 33 mA, use a 180 ohm, 1/2 watt resistor. The resistor value may have to be adjusted to match the actual discharge rate of your battery. If the discharge rate is much higher than 33 mA, look for a sneak discharge path in the tractor electrical system. Another approach is to use an LM117 regulator to drop the main-tenace charger output. Set its output to about seven volts.

Joseph D'Airo West Islip, NY

#5 Here are two sites where six volt chargers are available: www.atbatt.com/product/6840.asp and www. batterystuff.com/battery-chargers/6-volt/UPG6.html

If you want to Figure 2 build your own float charger, refer to Figure 2. A 12 volt DC wall wart such as stock #16770 from www.mpja. com can be used with the circuit.