Nuts and Volts - November 2011

READER-TO-READER TECHFORUM

the cost of energy is a concern. The
four scenes and off modes are
selected by a momentary contact
closure. The manufacturer solution is
to upgrade to digital control. Is there a
circuit design using a microcontroller
that could capture the state the
controller was in at the time of the
power failure and restore the
controller to the mode after power is
available?
#11116

Philip Popiel Thornton, PA

BASIC Stamp Help Needed

I am a beginner using a Parallax BASIC Stamp kit #555-28158. How do I wire seven LEDs and program them to come on and off in certain orders or patterns? Is it possible with this kit?

#11117 Saul

Odessa, TX

Long Range Wireless RS-232 How can a long range wireless

RS-232 link between two computers be built? I'd be very interested in how to get an effective range of 3-5 miles.

#11118 Todd Norvell via email

Loudspeaker/CB Combination

I was wondering if it would be possible to cheaply build a system in which I speak into a CB type radio, and have the signal sent to a loudspeaker about 1,000 feet away or slightly more? The current system I have is a bullhorn, and I have to stand a good distance back from the crowd to accomplish my task. It kills my voice. I was thinking if I could buy a loudspeaker (what wattage?) and a set of CBs that I should be able to modify the other CB to feed into the amplified loudspeaker so I can simply talk into it.

Surely there is a commercial version, but I'd like to be able to do it on the cheap if possible.

#11119 Daryl McIntire

Seneca, SC

used as a "Recording" light in a small studio. Ideally, the sign would come on fully for several seconds at first, and then flash on and off slowly, ramping the voltage to the display or LEDs up and down, so as to create a soft blinking display.

#111110 Al Parry Preston, MD Jon Titus Herriman, UT

“Suppose you want a microcontroller (MCU) to adjust the intensity of LED light. You could use a motor to turn a potentiometer that adjusts a transistor's base current, but that approach doesn't make sense, and many MCUs offer a better way to control intensity.

Those MCUs include at least one pulse-width modulator (PWM) output. This output creates a signal that varies between, say, three volts and zero volts at a preset pulse period, as shown in Figure 2. Software varies the pulse width. If the MCU creates a PWM signal that looks like a square wave, the voltage exists at three volts for 50 percent of the time and at ground for 50 percent of the time.

The MCU can adjust the pulse width — thus it modulates the pulse width — so you could have a series of pulses at three volts for 10 percent of the time and at ground 90 percent of the time. The percentages of on and off times always add to 100 percent.

If you use this signal to control a transistor that operates as a switch, the LED would turn on only 10% of the time. Because your eye cannot respond quickly enough to the frequency of the pulses, the LED simply appears dimmer.

You can use a MCU such as the Microchip Technology PIC16F690 in the PICDEM Lab Development Board kit (DM163035) to generate a PWM signal controlled by software. Then, a program will vary the brightness of one or more LEDs between off and full on.

Here's an overview of how to use the 16F690 PWM signal "generator." This description applies only to this MCU. Other MCUs also have PWM sections, but require different settings.

>>> ANSWERS

>>>YOUR ELECTRONICS QUESTIONS ANSWERED HERE BY N&V READERS<<< Transformer Needed

[#10111 - October 2011]

PIC16F690

What is the easiest or best way to PWM a PIC16F690? I've seen Chuck Hellebuyck's book, but he uses an external pot to manually do it. I need to do it in software.