# Project using LEDs and Switches

Discussion in 'Electronic Basics' started by Ken, Nov 26, 2003.

1. ### KenGuest

Hey, I'm pretty new to electronics and I decided to start by building
a simple circuit using some LEDs, some switches, and a DC adapter. Not
very fancy, there are 5 groups of LEDs wired in parallel, each with
its own unique switch, but they all share the DC adapter for power
(only one set of lights needs to be on at one time, so I'm not worried
about regulating the amount of current). Using ohm's law, I
calculated the correct number of LEDs to use in each group to divide
the current down to an appropriate level. Now for my problem:

When i flip any of the switches, every group comes on. I realize
that this is in some way because they all share a common power supply,
but beyond that I'm stuck. I read somewhere that a diode might solve
this. I'm not entirely sure how a diode would help though. If
electricity flows from negative to positive, why do I need to
introduce a new structure for doing that? Or am I not getting the idea
of diodes? I don't even though if that's the right way to go. I read
somewhere else about logic gates, which also seems like a possible
solution. However before I continue, I'd like to try and understand
exactly what's going on. Any help anyone could give would be greatly
appreciated.

2. ### John FieldsGuest

---
How many LEd's are there in each set?
What current are the individual LED's rated for?
What color are the LEDs/what is their rated forward voltage?
Are you mixing colors in a set?

3. ### RDGuest

? give us some idea of the circuit, this should work.

| | |
\ \ \
Switches
| | |
LED LED LED or more than one
| | |
R R R
| | |

It's easy to blow an LED with over current so you should use a limiting
resister
RD

4. ### KenGuest

How many LEd's are there in each set?
16
Green, Yellow, and Red (I believe they range from 1.8 - 2.2 volts)
Yeah, two of the sets have a mix of Green, Yellow, and Red
300 mA at 3 volts

5. ### KenGuest

? give us some idea of the circuit, this should work.

Yeah, minus the resistor that's what i have, except the switches on
the other side, i guess what you would call the "hot" side??. (DC-)
goes to all the switches and all the LEDs go to (DC+). Could this be
my problem?

6. ### John FieldsGuest

Since your supply is 3V, you won't be able to run any LEDs in series so
you'll need to use a separate resistor for each LED. You can determine
the value of the resistor by subtracting the LED's forward voltage from
the supply voltage and then dividing the difference by the LED current.
For example, with a 3 volt supply and an LED Vf of 1.2V, R =
(3V-1.2V)/0.02A = 90 ohms. 91 ohms is a standard 5% value, and to
determine the wattage the resistor needs to dissipate you take the
difference between the supply voltage and the LED Vf and multiply that
by the LED current: P = (3V-1.2V)*0.02A = 0.036 watts, so you could use
a 1/4 watter.

Arrange your switching like this and you should be fine:

(View with a fixed pitch font like Courier)

GND>-----------------------+
|
3V>--+--> | |
| | |
| O SET 1 |
| | |
| +--[R]---[LED>]--+
| | |
| +--[R]---[LED>]--+
| . .
| . .
| . .
| +--[R]---[LED>]--+
| |
| |
+--> | |
| | |
| O SET2 |
| | |
| +--[R]---[LED>]--+
| | |
| +--[R]---[LED>]--+
| . .
| . .
| . .
| +--[R]---[LED>]--+
| |
. .
. .
. .
TO REMAINING SETS

7. ### Watson A.Name - Watt Sun, Dark RemoverGuest

What's wrong with Google? Has it gone stark-raving mad? I did a
search for Wire OR, and came up with 17,500,000 hits. So then I put
it in quotes, and _still_ got 17,500,000 hits! So I changed it to
"wire OR circuit" and I got 19,500,000 hits!!!

Anyway, when Google regains its sanity, do a search for Wire OR
circuit. :-/

--
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###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@

8. ### Watson A.Name - Watt Sun, Dark RemoverGuest

You should use Courier or other fixed space font so your drawing
doesn't come out all whacko.

--
@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@

9. ### Robert MonsenGuest

I'm trying to determine exactly how your circuit is connected. You have a 3V
dc source, and the anode (long lead) of a bunch of LEDs are connected
directly to it. Then, for each LED, you have a separate switch. One side of
the switch connects to the short side of the LED, and the other side of the
switch connects to 0V (the DC- or ground).

When you turn on one of the switches, all the LEDs turn on.

Is that right?

Regards,
Bob Monsen

10. ### KenGuest

Since your supply is 3V, you won't be able to run any LEDs in series so
The side that says "3V" is positive and "GND" is negative, right? I'm
talking about as they would be marked on my DC adapter (the wire with
the white strip being positive), not in reality, because I know that
negative and positive are actually switched right?

Would what side I'm putting the switches on actually make a
difference? And for that matter, what side should the resistors go on?
I assume it would be where the current flow originates from in
relation to the LED, like on the positive side (which in reality is
the negative side). Does this sound right?

11. ### KenGuest

Yeah, minus the resistor that's what i have, except the switches on
Yeah, that's right. Each group of LEDs is connected its own switch.
Every switch is hooked to (DC-) and every group of LEDs is hooked to
(DC+).

12. ### Ian StirlingGuest

I think you'll find that that's the way it's supposed to work.
OR means special things.
Searching for
wire diode matrix
may help.

13. ### Peter BennettGuest

Yes - "3V" is the positive side of your supply, and "GND" is the
negative.

I don't understand what you mean by "not in reality..." - positive is
positive, and negative is negative.

In a series circuit, the parts can go in any order. You can put the
resistors on either side of the LEDs, and you can put the switches on
either side of the LED/resistor combination. The only requirement on
position or direction is that the LED cathode must be nearer the
negative supply, and the anode nearer the positive supply.

The "direction of current flow" is irrelevant here.

Most people talk of current flow as a movement of (mythical) positive
charges from the positive terminal of the power source, through the
circuit, and returning to the negative terminal, even though we know
that in most materials, current is really a movement of negatively
charged electrons from the negative terminal of the power source,
through the circuit, returning to the positive terminal. The "flow of
positive charge" concept is called "Conventional Current".

14. ### Peter BennettGuest

If all the LED groups turn on when you turn any switch on, then things
must not be wired as you think - you must have connections between the
switch sides of the groups of LEDs.