# New to electronics.

Discussion in 'Electronic Basics' started by anon, May 14, 2005.

1. ### anonGuest

Hi to all

I'm just getting into electronics as a hobby because i've had to retire from
work due to illness and thought i could do with something interesting to pass
the time.

I've decided to try my hand at some "breadboarding" to start me off.

I saw a link for http://www.doctronics.co.uk/index.htm in one of these
electronics newsgroups, so i had a look to find out if the website would be of
any use to me.

I noticed a project for a games timer which i thought i'd try my hand at. I sent
off for the components, complete with instructions, and bought myself a couple
of breadboards and some other bits and pieces to start me off.

On ebay, i saw a new (and fairly cheap), bench top power supply which i thought
would be better than having to keep buying batteries for the various projects
that i would be undertaking.
It is switchable between 3, 4.5, 6, 7.5, 9 and 12volts dc. The current rating is
1500ma max.

I was just wondering, as i'm new to electronics. Would the current of 1500ma
max, be flowing whatever the voltage might be (ie: 3, 4.5, 6, 7.5, 9 or 12volts
dc) - or would the current flow be dependent on the components being used in the
circuit, upto a maximum of 1500ma using the above power supply ?.

Thanks in advance for any help with this question.

hermit50

2. ### Tom BiasiGuest

The 1500 mA is the maximum rating of the supply. This means that no matter
how you use the outputs the total current draw should not exceed 1500 mA.
To better understand this do a search for E=IR, or Ohm's law. Learn the
relationship between voltage, current, and resistance well.
Good luck,
Tom

3. ### Joe McElvenneyGuest

Hi,

1500mA is the maximum that the power supply is capable of providing. The actual
current drawn will depend on the circuit connected to it and the voltage you
choose to supply it with. It is simply Ohm's Law which states (in the form you
need) that the current taken will be equal to the voltage divided by the load
resistance. The load resistance is that which the circuit presents to the power
supply.

Now this load resistance will vary widely from circuit to circuit but it is
fairly safe to assume you will only need a small handful of mAs for that project
and so have plenty of headroom. I suggest you spend just a little more money and
buy a digital multimeter which will have a DC current range, so that you can
monitor it and learn some basic theory in the process. They usually cost just a
few dollars for a perfectly useable device and these days can even be found in
supermarkets.

Cheers - Joe

4. ### Lord GarthGuest

Look for a 5 volt regulated supply too.

5. ### hermit50Guest

Hi again

Thank you all for the replies answering my question.

I have bought myself a digital multimeter, (i did already have an old analog
one).
I've also got a copy of Ohm's Law which i am currently (no pun intended)
absorbing.

Current = Voltage / Resistance. (I = E / R).

Resistance = Voltage / Current. (R = E / I).

Voltage = Current x Resistance. (E = I x R).

Power = Voltage x Current. (P = E x I).

I recently acquired a secondhand 20MHz Hameg 203-4 dual trace oscilloscope,
including x1 / x10 probes and manual, which will come in handy at some point
along the way in my new hobby.

I expect i will be back on this newsgroup to ask other important questions in
the (near) future but, for now, i'm off to do some more reading on this
facinating subject - i think i'm getting hooked.

Thanks again all

hermit50

6. ### DwayneGuest

that should help get you started with DC circuits.

(1) Ohms law:

V=I*R

Voltage (measured in Volts) is the product of current (Amperes or Amps for
short) and resistance (Ohms). The important thing to realise is that you
need a change in voltage to get a current to flow. The equation should

V2-V1=I*R

Think of a garden hose, if there is no difference in pressure between the
water in the pipe and the air in the atmosphere then you would be hard

(2) Power

P=V*I

Power (in Watts) is the product of voltage and current. Ohms law can be
inserted into the power equation to obtain equivalent statements namely;

P=V^2/R
P=I^2*R

Also power supplied to a circuit will be absorbed by a circuit. If you apply
too much power to a component it will smoke and fail. A resistor for example
will have a value of resistance say 100 Ohms and value for power say 0.25
Watts.

P= V^2/R
0.25=V^2/100
V^2=100*0.25
V^2=25
V=5 Volts

V=I*R
I=V/R
I=5/100
I=0.05 Amps
or
I=50 mA

So if you apply 5 Volts across (ie: V2-V1) a 100 Ohm resistor you will need
to suppy 50 mA (milliamperes) of current.

(3) Kirchoff Voltage Rule

The sum of the voltages around any closed loop must equal zero. This is
based on the assumption that your supply can produce enough current for your
load/circuit. If not then your supply will only apply enough voltage to
satisfy the maximum current.

(4) Kirchoff Current Rule

The [sum of the] current into a node (junction) must equal the [sum of the]
current leaving the node.

I hope this helps,

Dwayne

7. ### Charles JeanGuest

Here's my list:

Digital VOM-cheap one-let's you measure the 3 variables in Ohm's
Law-volts, ohms, amps. Gotta know Ohms law. The cornerstone of the
electronics building.

Good NiMH battery charger with AA size NiMH batteries. I use a Power
Port Model BC-101-U. Individually charges up to 4 AA or AAA batteries
at one time, based on deltaV/deltaT. Batteries can also be used for
all the other battery-powered things around the house.

Battery holders for the above. 1/2/3/4 battery capacities available.
Lets you experiment with various voltages and power your early
either 5 volts(4 AA batteries, 4.8-5.2 volts, depending on charge
state) or a 9 volt alkaline.

A sprinkling of 1/2 watt resistors, spanning the range of 10 ohms to
10 megohms. ~\$0.05 ea.

Various-colored LEDs. ~\$0.05 ea.

This will give you enough to learn about Ohms law, the correct way to
wire in some LEDs and figure the resistor required for it to work
without letting the magic smoke out, etc. Besides Ohms law, read
building your own power supply using a "wall wort", couple of
capactitors and a 7805 voltage regulator chip.

Welcome to the fray.

Cheers!
Charlie

8. ### hermit50Guest

Hi Charlie

I've already got most of the items you listed above:

Digital VOM
Various battery holders & connectors
Various coloured LEDs
Various types & sizes of Resistors, Diodes, Zener Diodes & Capacitors
Various sizes of DIL Sockets
Various transistors.

I've also got a copy of Ohm's Law, i did a search on google & found a copy of
"Kirchoff's Laws" as mentioned by Dwayne in a previous post.

Now it's down to some experimenting with some circuits.
The first of which is going to be a "games timer" as described on the following
website:
http://www.doctronics.co.uk/kits.htm#games

Thaks again

hermit50

9. ### Charles JeanGuest

Looks like an ambitious "first" project. The Dontronics kits are very
good, and instructions are detailed, and theory well explained. With
a kit like this you will be dealing with low frequencies, so you can
"see" the pulses by using an LED and measure them with a stopwatch.
When you get to frequencies much higher than 2-3 cps, though, this
becomes pretty hard to do with just an LED. Then you're going to need
either a frequency counter or an oscilloscope. The oscilloscope is
more flexible. You can find used ones on EBay and the like.
"There are known knowns. These are things that we know we know.
There are known unknowns. That is to say, there are some
things that we know we don't know. But there are also unknown
unknowns. These are things we don't know we don't know."
-Secretary of Defense Donald Rumsfeld

10. ### hermit50Guest

Hi Charles

I thought the Doctronics project would be a good starting point for me to get

I recently bought a secondhand 20MHz Hameg 203-4 dual trace oscilloscope,
including x1 / x10 probes and manual - which i got on ebay.

I think it will come in handy with the projects.

--
hermit50

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