Electronics Forum / Basics / August 2007

can anybody help me by prescribing some books on basics of electronics

Can sombody check my math to see if this LED resistor value is right?
I have a series chain of 25 white LEDs at 3 volts each. I want to
connect them through a resistor to a bridge rectifier connected to the
120VAC line. There is a 50uF capacitor across the chain of LEDs. What

I am building an 8 x 80 scrolling LED sign for fun.  The basic design
centers around an Atmel Mega88 microcontroller which is connected to a
4-to-16 decoder and 5 74hc595 shift registers.  The individual
matrices (each measuring 8 x 8, 10 in total) are arranged in a 2 x 5

   I have a 50 pin ribbon cable that is carrying a large number of
signals from various hardware components in a medical device I am
trying to test.  I'm looking for a device/connector that would allow
me to gain direct access to any one of the wires/pins in the cable, so

Dear friends,
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free electronics video lessons web casts  http://freevideolectures.com/electronicsdesc.html
. It has on all the topics of mathematics. Absolutely free. No

wanted to ask following questions, just out of curiosity:
About visible light being electromagnetic radiation:
1. since visible light is essentially electromagnetic radiation, has
any experiments been made to take, let's say radiowaves, and increase

I've made a DC power converter, and I've got extra voltage.
I'm using a physically large 15-1 transformer to reduce the voltage,
and I'm getting 7.9V AC over leads 1 and 2, and over leads 2 and 3,
with 16.2V over leads 1 and 3.  I made a bridge rectifier, and on the

I've got a simple question... it's been a while since my last
electronics lab,
and I'd appreciate a quick help/answer.
If I put two Avalanche/Zener diodes in series, and apply reverse bias,

(crossposted)
Looking at the 1/16" x 1/4" red rubbery extrusion from the
non-functional end of a DC motor. It looks like heat shrink tubing
over a much shorter extrusion, but it's softer and I don't see any

Hello, I am trying to interface with a device that outputs 24V when
off and switches to 0v when commanded on.  The problem is, I need 0v
when off and 24V when commanded.  I tried to use an opamp as a
comparator to swap the voltages but have not been successful.  Is

I have a 5V and a 12V power supply. Both have a N, L, Ground
connections for the AC side. Both also have a V- and V+ connection.
Measuring between V- and V+ I get the correct voltages, i.e. 5V and
12V. Measuring between ground (AC side) and V- on both the 5V and 12V

Those green circles you see from the air are produced by a bridge like
structure called a "pivot" that rotates while irrigating the crop.
Up to 1/4 of a mile in length, the pivot could be jazzed up to do more
than irrigate:  It could replace the tractor altogether.

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excuse me Ihave a project about ultrasonic for measurment of distance
beetween two cars!
its not for avoidance of hit!it for reducing the speed to keep the
standard distance between  two car

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