Building Simple Circuits

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Greg's Basic Electronics

Instructional eBooks

Introduction To Basic Electronics

Building Simple CircuitsBy GS Carpenter

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hile all attempts have been made to verify information provided in this publication, the Publisher assumesno responsibility for errors, omissions, or contrary interpretation of the sub!ect matter herein. "ny perceivedslights of specific persons, peoples, or organi#ations are unintentional.

"ll rights reserved. $o part of this boo% may be resold, reproduced or transmitted in any form or by anymeans, without prior permission of the publisher.

&ou are encouraged to print this boo% for your own easy reading.


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NOTE... This eBook is the companion book to "Introduction To BasicElectronics" and that book should be read first.

$ow it's time to actually get some hands(on e)perience with somesimple basic circuits.

IMPORTNT! Please read throuh this before #ou start to build.

Before we get started, there are a couple of things we need to tal% about. *ne

is soldering techni+ues and the other is getting the right components youneed to complete this very important section of this mini course.

$olderin

Proper soldering is so very important in todays printed circuit world. *ne badsolder !oint can cause an entire pro!ect to fail.

The good news is that it's pretty easy to learn if you get started on the rightfoot and do a little practice.

"lthough most people will build these circuits using a solderless breadboard, Iwill be building them on a piece of circuit board material so you can see howit's done.

It's perfectly *- if you use solderless breadboard to build yours.

Parts

"s far as components go you will need a few /0 watt resistors. 12 034 ohm,152 444 ohm and 12 4- ohm will get you started.

&ou will also need a few red or green 678s and a few $P$ general purposesmall signal transistors li%e the 5$5555 and a 5544 microfarad 9 volt ormore capacitor.

&ou can pic% all of these up at many electronic parts outlets online or placesli%e :adio shac%.

*- let's build some simple circuits and ma%e them wor%.

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Building Simple Circuits

" Series :esistor Circuit

CI:C;IT *$72 between the tworesistors to ground. :ight=

*- here's what will happen.

The capacitor is discharged so it wants to grab all the energy it can which atthis point, gives it a near #ero ohm resistance. So thin% of it as a #ero ohmresistor right now.

6oo% again at the diagram and thin% about what happens when a #ero ohm

resistor is placed where the capacitor is.&ou will see current flow from the battery through the - resistor through theimaginary 4 ohm resistor bac% to ground. 8o you see that=

"ll the current is flowing through the - resistor.

$o voltage is applied to the 034 ohm resistor and 678 because the capacitoris at #ero ohms holding everything at ground which is #ero volts.

If this helps, since the capacitor is right now at #ero ohms you can thin% of itas piece of wire across the terminals.

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CIRC%IT 0O%R!

Capacitor Chare nd 1ischare

$ow some time has gone by and the capacitor is charging, its resistance is

going up and up as it charges and when it's completely charged it'sresistance will be e)tremely high in the millions of ohms.

Eow long will this ta%e=

That is dependent upon the value of the series resistor and in this case it'sthe -.

Na%ing the resistor or the capacitor larger will increase the time to charge andma%ing it smaller will decrease the time.

This is %nown as the :C time constant.

Bac% to the circuit, as the capacitor charges it draws less and less currentwhich is the same as saying it's resistance is going up and up.

$ow remember way bac% to the two resistors in the series circuit, when thetwo resistors were e+ual in value the voltage across them was the same.

In our circuit it was 0. volts across each, which e+ualed the applied voltageof ? volts.

@


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CIRC%IT 0O%R!


*-, so at some point the capacitor's internal resistance will be passing -and at that moment we will see 0. volts across it.

That same 0. volts is also being applied to the 034 ohm resistor and 678.

The 678 should be dim but getting brighter now.

Nore time has gone by and the capacitor is now fully charged. It's internalresistance is now in the megohms so it is essentially out of the circuit and allwe have are the two resistors and the 678 in series, across the ? volt battery.

"t this point the 678 is at it's brightest.

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'ere2s ho( to build it.

Start with the capacitor.

Solder the negative lead, the one near the band or mar% that indicates thenegative lead on these type of capacitors.

IMPORTNT TIP!

This applies only to capacitors with leads, surface mount types also have a

band, but it indicates the positive end of the capacitor.

I really found that out the hard way

Solder the negative lead of the cap. to lug A0 ground and the positive lead tolug A@.

$e)t solder the 678 cathode to ground 1lug A02 and then the 034 ohmresistor to the anode lug A and to lug A9.

@@


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$e)t run the piece of hoo% up wire from lug A9 over to lug A@. That ties the034 ohm resistor to the capacitor as in the diagram.

$ow solder the - ohm resistor from lug A 1J?volts2 to lug A@ and you're setto go.

Eere's what the solderless board loo%s li%e.:K- :5K034 CK5544u> 8K 678

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*- $ow lets test this thing...

hile watching the 678 hold the battery to the connector, but don't snap it in.

The 678 will fade on as the capacitor charges, but... now remove the battery

from the connector.

The 678 stays on without the battery and then slowly fades out.

hen the battery was been removed the capacitor began dischargingthrough the 678 until it was discharged.

atch and try it again.

hen you disconnected the battery the capacitor became the FbatteryF andpowered the circuit until it was discharged.

8oes this mean that a capacitor is a battery=$o. " battery uses chemical reactions to produce voltage and current. Itdoesn't store energy, li%e most people thin%, it produces energy.

hen you recharge a battery you are reversing the chemical reactions bac%to where they started so they can do their thing again.

*n the other hand a capacitor stores its energy as an electric field, butdoesn't produce any energy on it's own.

$ow let's !ump out and into the real world of everyday electronics and let me

show you something that will surprise you, because you will discover that younow %now e)actly how it wor%s

Eere it is... It's a common low voltage 8C power supply.

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4o( 3oltae 1C Po(er $uppl#

&ou don't need to build this, I !ust thought we could ta%e a few minutes andloo% at something you have learned about without %nowing it.

&ou might recogni#e C, : and 85 from the circuit you !ust built.

$ow I added some new symbols, the power plug, a fuse > an on/off switchS. 7verything else you will recogni#e from the course. T is a step down

power transformer and 6 is an inductor.$ow let's run through it.

:emember, we are using "C voltage here so the primary winding of thetransformer T is 'seeing' a changing current and changing magnetic field.

This changing field induces a voltage in the FsecondaryF winding of T. Theamount of voltage depends on the turns ratio of the windings. If thesecondary has fewer turns then the primary you have a Fstep downFtransformer. If it has more than the primary, it's a Fstep upF transformer.

In this low voltage power supply we will call for a step down to 5 volts "C.

If we used a 4


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4o( 3oltae 1C Po(er $uppl#

*-, from the top of T's secondary a wire connects to the anode of diode 8.It's very important to connect to the anode as we want a positive voltage.

If it got connected to the cathode we would get a negative voltage and thesupply would not wor%. It would damage the capacitor and if the capacitorfailed as a short, then the fuse would blow and hopefully protect the diodeand the transformer So watching polarities is e)tremely important

The diode 8 conducts only on the positive half cycles of the alternating

current from the transformer, so the output of the diode is positive pulses, thepositive half of the input sine wave.

$e)t a wire connects to the inductor 6 and then from 6 to capacitor C.

The combination of 6 and C forms a low pass filter. 7ach time a positivepulse arrives at C it charges up, then during the time between pulses itdischarges supplying current to the load until the ne)t pulse arrives. Thisfiltering action is what gives a nice smooth 8C output.

$e)t a wire connects to :. This resistor is called a dropping resistor and is

used to reduce or drop the voltage supplied to 85 the 678 diode. The 678 isforward biased and will light when the power supply is turned on.

If there is no load on the power supply 1as in this drawing2 then the 678 willslowly go out when the supply is switched off due to the capacitor Cdischarging though the 678 until it has completely discharged.

See, you pretty much %new e)actly how that wor%ed without me e)plaining itto you. *- you are ready to go out on your own because you now have agood basic understanding of basic electronics.

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If you were able to build all of these circuits and get them to wor%, then youare ready now to build real pro!ects on your own.

Be sure to visit my website. There you'll find a list of other simple to buildpro!ects li%e audio amplifiers and "N broadcast radios.

So don't stop now because you really on your way to understandingelectronics, a very important s%ill in todays world.

Greg Carpentergregsbasicelectronics.com

P.S.

I thought you might li%e to see the corner of my wor%shop where I design andbuild these circuits to show you that it doesn't ta%e hardly any room at all todo this.

Eave fun with your new s%ills.
http://gregsbasicelectronics.com/http://gregsbasicelectronics.com/

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Building Simple Circuits