Basic Electronics 101

[saint]

V=IR.

Assuming a constant amperage (I can assume that in an arcade cabinet hack of a PC power supply to, say, a Perfect 360 joystick, right?)... the following is true:

To raise voltage, you add a resistor in series. To lower voltage, you add a resistor in parallel.

Correct?  And if I want to alter amperage with a constant voltage, then the opposite is true:

To raise amperage, you add a resistor in parallel. To lower amperage, you add a resistor in series.

====================

Did I get that right?  

--- saint

[Tailgunner]

Don't think so. The only way I know you can raise the voltage is through a transformer.

[usedelectronics]

V=IR.

Assuming a constant amperage (I can assume that in an arcade cabinet hack of a PC power supply to, say, a Perfect 360 joystick, right?)... the following is true:

To raise voltage, you add a resistor in series. To lower voltage, you add a resistor in parallel.

Correct?  And if I want to alter amperage with a constant voltage, then the opposite is true:

To raise amperage, you add a resistor in parallel. To lower amperage, you add a resistor in series.

====================

Did I get that right?  

--- saint

Not entirely.
If your source is a fixed voltage, the voltage across both parallel resisistors is the same. The currents are different.
In a series circuit, both resistors see the full circuit current, but not the same voltage.

[Syntax]

V=IR.

Assuming a constant amperage (I can assume that in an arcade cabinet hack of a PC power supply to, say, a Perfect 360 joystick, right?)... the following is true:

To raise voltage, you add a resistor in series. To lower voltage, you add a resistor in parallel.

Correct?  And if I want to alter amperage with a constant voltage, then the opposite is true:

To raise amperage, you add a resistor in parallel. To lower amperage, you add a resistor in series.

====================

Did I get that right?  

--- saint

Nope a resistor in series or parallel with both lower voltage.  

[knuttz]

A resistor in series will lower voltage and will not alter current to the load, A resistor in parallel will lower current and not alter voltage to the load.  To increase voltage one must use an op-amp or transformer.

..... I think

[usedelectronics]

A resistor in series will lower voltage and will not alter current to the load, A resistor in parallel will lower current and not alter voltage to the load.  To increase voltage one must use an op-amp or transformer.

..... I think

Correct.
However when using a transformer to increase voltage, one does so at either the sacrifice of current capability, or puts a much higher demand on the pre-transformer supply.

Also,  op-amps do not "amplify" signals, they are merely a means of controlling a larger supply voltage. I.E. a small signal in, controls a larger signal (from a different voltage source.)
The output of a op-amp circuit can not exceed the voltage supplied to it. (Without the use of voltage doublers/transformers).

[tiggertoo]

The problem is you're assuming that you can change the voltage. Most power supplies only provide you with a constant voltage. (In a lab environment you may have variable supplies).

So, the only things you can change are your amps and your resistance. And resistance is what changes your amps. The more resistance, the less amps.

Now, resistors in series are additive. So the more you put in series the less amps you have and the amps are the same throughout the series circuit.

Resistors in parallel reduce the resistance by some complex formula (not really) that are not part of the 101 class (please proceed across the hall to 103). Anyway the effect is to increase the overall current of the circuit, however each leg of the parallel circuit will have a fraction of the total current of the circuit.

For your purposes, the only way to get more voltage is to use a different power supply that provides the voltage you require.

[tiggertoo]

Actually, that last statement is not 100% correct. You may find a voltage doubler/multiplier that suits your purpose. I have no experience with them tho'.

[hyiu]

my $0.0002 cents of lmiited knowledge in electronics...

if you have a constant power source....
(like the 5V supplied by the computer molar connector....)

the power source will always be 5V (assuming you did not load it with power hungry circuits / gagets....)

unless you use a transformer... the voltage will stay the same...

now... assume you hook resistor in series...

then the voltage will be split depending on the resistance of the resistors... but the SUM of the voltage will be 5V....

if you hook the resistors in parallel... then the voltage of each resistors will be 5V.... but the current flowing thru will be different depending on each resistance....

if you use a transformer.... I believe... Power (Watt) = Voltage x Current.... so, if you use the transformer to raise the voltage... then current will be lower.... and vice versa...

(of course... we're talking about "ideal" case where there's no lost and perfect efficiency....)

but with my very limited knowledge on this... I think with a 5V DC supply... and just using resistors... I don't think you can raisethe voltageto more than 5 V......

maybe you can let us know what you want to achieve... and then there should be enough guys here to give you plans on how to approach it !!...    

hope it helps....  

------------------------------------------

on easier terms.... always think about power....
but not just voltage or current...

         power supply   5V x 200mA
------------------    5 V     --------------------
|                                                              |
---------- R ------------------ R -------------
           2.5V                     2.5V
        200mA                    200mA

current is the same... voltage cut in half....
in this case... assume resistance of 2 resistors are the same...



         power supply   5V x 200mA
------------------    5 V     --------------------
|                                                              |
---------------------- R ------------------------
|                         5V - 100mA                      |
|                                                              |
---------------------- R ------------------------
                       5V - 100mA

voltage is the same... but current cut in half....



         power supply   5V x 200mA
------------------    5 V     --------------------
|                                                              |
----------------XXXXXXXX---------------------
                      XXXXXXXX   transformer
                      XXXXXXXX
                      |          |
                  10V x 100mA
(or any combination where the power will stay the same.....)

hopefully... I know what I'm saying here and its not BS....
 

[tiggertoo]

Just a quick point:

With all the talk about transformers - they are pretty useless in a DC circuit. Transformers work with oscillating circuits or AC current. DC is always constant, so a transformer will not work, unless you want to create oscillations.

[RandyT]

Just a quick point:

With all the talk about transformers - they are pretty useless in a DC circuit. Transformers work with oscillating circuits or AC current. DC is always constant, so a transformer will not work, unless you want to create oscillations.

Too true.  That's exactly what you would have to do.  A quick search brought up an RC timer circuit with 2 transistors and a transformer.  It would probably take a bit to convert it back to usable DC though.

Oh, and a variable voltage regulator circuit can be used for dropping voltage.  A far better choice than just resistors if you need a big change (like 12v to 5v).

FWIW,
RandyT

[BobA]

V=IR.

(I can assume that in an arcade cabinet hack of a PC power supply to, say, a Perfect 360 joystick, right?)

--- saint

If a perfect 360 is going to be connected it uses a 5V supply which is provided by the PC power supply so no hack is needed.

BobA

[grafixmonkey]

you guys are confusing me........

You can use the V = I * R equation on resistors at all times.  The problem is, you have three variables to work with, so you have to think about what is going to stay constant and what will change when you modify either V, I, or R.

If you have a resistor on a voltage supply, the voltage supply does its best to keep a constant voltage - so I and R can change, and if you know one you can find the other.  i.e. putting a resistor across a 5v supply and then increasing it won't make the supply run at 7v.  It will make the current decrease.

If you have a resistor on a current supply (these don't occur very often) then the supply provides a constant current, and V and R can change.  (know one and you can find the other etc. etc.)

There are some other basic laws of circuits that come together to allow you to figure out what's really going on (if you want to look them up they're called Thevenin's and Norton's laws).  

One is, if you have any loop of components in a circuit, regardless of anything else that might be connected to various points in the loop, if you add up the voltages across all the components in the loop (ending back where you started) the result will be zero.  So in basic terms, if you do the "voltage walk" around the wires and components in a circuit and end up at the same place you started, you will always be at the same voltage you started.

Another is, if you have any number of components attached by a single junction of wires (i.e. a solder joint and the components connected to the wires that are soldered together), if you add up all of the currents that are entering the junction (i.e. the current direction is important) then the result will be zero.  So in basic terms, the quantity of current that goes in through some wires, must leave through the others.

Anyway, those are the basic universal truths of circuits - there's no ifs or special situations to those, sometimes they are hard to use to get the answer you need, but just about all the other rules about circuits are derived from them.

So, say you have this situation:
(5V) ----/\/\/\/-----/\/\/\/----(ground)
          15ohms      35ohms

Then you have two resistors in series, which is like one resistor of 50 ohms.  You use that 60ohm number with  5v = I * 50, and get I = 0.1amps.  You now know that 0.1amps flow through that circuit.  So, the voltage across the 35ohm resistor obeys   V = 0.1 * 35, so the voltage across the 35ohm resistor is 3.5v.

[tiggertoo]

He-He, Graphixmonkey, I think you went past electronics 101.

I was just trying to keep it simple. Saint want's know how to increase the voltage out of a power supply and I was trying to tell him that this can't be done with just resistors.

But, hey, thanks for bringing up painful memories of Thevenin's theorum. I don't think I'll sleep well tonite.

But, seriously, you should make a primer for these guys.

[grafixmonkey]

what?   those are the basics!     (I guess I'm a nerd!   )

Actually, the extent to which people deal with LEDs and stuff, I thought those laws might be helpful to know.  The voltage loop law is useful for hooking up LEDs.  

Maybe you're right, a circuits primer that stays where people can see it might be a good idea.  Lots of questions pop up about whether you can stick two switches in parallel, and whether the shape of your ground loop matters.