| Author |
Message |
Mark Jerde
Guest
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 Posted:
Sat Nov 12, 2005 1:35 am Post subject:
Help Getting Started - Simple DC Circuit |
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(I apologize for posting this basic circuit question. 25 years ago in
college I had to know E=IR etc. Just having problems getting started...)
I'm trying to "invent" a mechanical device. I've been having some alignment
problems with it and this afternoon it occured to me some simple electronics
would help a lot. But it has been many years since I've done anything more
complicated with electronics than change batteries in the household smoke
detectors. ;-) I'm looking at the Jameco web site, seeing if I can find
enough info to play with E=IR but there are just too many options &
choices...
I want to go to my neighborhood Radio Shack and buy
- 30 ea SPST NO switches
- 30 ea green LEDs
- 30 (?) ea resistors to limit current to the LEDs
- A circuit board to solder the LEDs & resistors to
- A battery case (e.g. 4 "D" cells) or 9v clip
I have an electronics soldering iron and plenty of wire.
The goal: When everything is lined up right on my mechanical device, all
the switches will be closed and all 30 LEDs will be glowing. Then I'll
unplug the battery, as the machine is ok once all the switches are closed.
(E.g., no long-term lighting requirement.)
How can I get started with this? For the battery which value to use, 1.5,
3, 6 or 9 volts? Does each LED need its own resistor or is one resistor
enough? (I don't care how bright the LEDs are so long as they are visible.)
Thanks.
-- Mark
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Randy Day
Guest
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| Posted:
Sat Nov 12, 2005 1:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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Mark Jerde wrote:
| Quote: | (I apologize for posting this basic circuit question. 25 years ago in
college I had to know E=IR etc. Just having problems getting started...)
I'm trying to "invent" a mechanical device. I've been having some alignment
problems with it and this afternoon it occured to me some simple electronics
would help a lot. But it has been many years since I've done anything more
complicated with electronics than change batteries in the household smoke
detectors. ;-) I'm looking at the Jameco web site, seeing if I can find
enough info to play with E=IR but there are just too many options &
choices...
I want to go to my neighborhood Radio Shack and buy
- 30 ea SPST NO switches
- 30 ea green LEDs
- 30 (?) ea resistors to limit current to the LEDs
- A circuit board to solder the LEDs & resistors to
- A battery case (e.g. 4 "D" cells) or 9v clip
I have an electronics soldering iron and plenty of wire.
The goal: When everything is lined up right on my mechanical device, all
the switches will be closed and all 30 LEDs will be glowing. Then I'll
unplug the battery, as the machine is ok once all the switches are closed.
(E.g., no long-term lighting requirement.)
How can I get started with this? For the battery which value to use, 1.5,
3, 6 or 9 volts? Does each LED need its own resistor or is one resistor
enough? (I don't care how bright the LEDs are so long as they are visible.)
|
2 'C' cells in series should give you enough power
for short periods, and 3 volts will be sufficient
to light the LEDs. You could try 2 'AA' cells, but
I'm guessing they won't handle 30x0.02A = .6A for
very long (if at all).
Each LED&switch will need a separate resistor.
Don't try to parallel them thru 1 resistor; you'll
let the magic smoke out of the LED's. :(
To calculate the resistor values:
R = (Vcc - Vled) / Iled
where Vcc is the supply voltage, Vled is the
forward voltage drop of the LED, and Iled is the
operating current of the LED.
You can find a minimum R value for your LED's,
and try larger values that still give acceptable
brightness with less power consumption.
HTH |
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Mark Jerde
Guest
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| Posted:
Sat Nov 12, 2005 1:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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Randy & David -- Thanks for the replies.
| Quote: | 2 'C' cells in series should give you enough power
for short periods, and 3 volts will be sufficient
to light the LEDs. You could try 2 'AA' cells, but
I'm guessing they won't handle 30x0.02A = .6A for
very long (if at all).
Each LED&switch will need a separate resistor.
Don't try to parallel them thru 1 resistor; you'll
let the magic smoke out of the LED's. :(
To calculate the resistor values:
R = (Vcc - Vled) / Iled
where Vcc is the supply voltage, Vled is the
forward voltage drop of the LED, and Iled is the
operating current of the LED.
You can find a minimum R value for your LED's,
and try larger values that still give acceptable
brightness with less power consumption.
HTH
|
I'm just back from Radio Shack with a package of these to get started
thinking:
http://www.radioshack.com/product/index.jsp?productId=2062588&cp
20 assorted LEDs, 2 - 3V, 10-20 mA
(They were the only thing economical. Other LEDs were one or two per
package, $1.98 to $4.98. I'll get another package when I go to get the
battery holder & resistors.)
Am I reading the specs right to use Vcc = 3 V, Vled = 2.5 V and Iled = 15
mA?
R = (3 - 2.5) / 0.015
= 33.33 Ohms
When I did electronics many years ago most of the resistors were in the
kiloohm and megaohm range. 33 ohms seems wrong. Am I missing something?
Thanks again!
-- Mark
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Guest
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| Posted:
Sat Nov 12, 2005 1:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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You will want to make sure the source voltage is a greater than the
led's forward voltage and the current limit resistor voltage drop. I
think white Leds are about 3V and Red Leds are 1.7V, but be sure to
check.
David |
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tempus fugit
Guest
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| Posted:
Sat Nov 12, 2005 8:38 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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If you need that much quantity, don't go to RadioShack. Check out
www.mouser.com - they are WAY cheaper and have no minimum.
"Mark Jerde" <MarkJerde@newsgroup.nospam> wrote in message
news:Y%adf.1862$rO4.1388@trnddc05...
| Quote: | Randy & David -- Thanks for the replies.
2 'C' cells in series should give you enough power
for short periods, and 3 volts will be sufficient
to light the LEDs. You could try 2 'AA' cells, but
I'm guessing they won't handle 30x0.02A = .6A for
very long (if at all).
Each LED&switch will need a separate resistor.
Don't try to parallel them thru 1 resistor; you'll
let the magic smoke out of the LED's. :(
To calculate the resistor values:
R = (Vcc - Vled) / Iled
where Vcc is the supply voltage, Vled is the
forward voltage drop of the LED, and Iled is the
operating current of the LED.
You can find a minimum R value for your LED's,
and try larger values that still give acceptable
brightness with less power consumption.
HTH
I'm just back from Radio Shack with a package of these to get started
thinking:
http://www.radioshack.com/product/index.jsp?productId=2062588&cp
20 assorted LEDs, 2 - 3V, 10-20 mA
(They were the only thing economical. Other LEDs were one or two per
package, $1.98 to $4.98. I'll get another package when I go to get the
battery holder & resistors.)
Am I reading the specs right to use Vcc = 3 V, Vled = 2.5 V and Iled = 15
mA?
R = (3 - 2.5) / 0.015
= 33.33 Ohms
When I did electronics many years ago most of the resistors were in the
kiloohm and megaohm range. 33 ohms seems wrong. Am I missing something?
Thanks again!
-- Mark
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Peter Bennett
Guest
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| Posted:
Sat Nov 12, 2005 9:24 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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|
On Sat, 12 Nov 2005 00:51:04 GMT, "Mark Jerde"
<MarkJerde@newsgroup.nospam> wrote:
| Quote: | I'm just back from Radio Shack with a package of these to get started
thinking:
http://www.radioshack.com/product/index.jsp?productId=2062588&cp
20 assorted LEDs, 2 - 3V, 10-20 mA
(They were the only thing economical. Other LEDs were one or two per
package, $1.98 to $4.98. I'll get another package when I go to get the
battery holder & resistors.)
Am I reading the specs right to use Vcc = 3 V, Vled = 2.5 V and Iled = 15
mA?
R = (3 - 2.5) / 0.015
= 33.33 Ohms
When I did electronics many years ago most of the resistors were in the
kiloohm and megaohm range. 33 ohms seems wrong. Am I missing something?
|
Red, yellow and green LEDs are around 2 volts, and I find they are
quite bright enough with 10 mA, so, with 3 volts, you could use 100
ohms.
Blue and white LEDs want about 3.6 volts, I believe, so you'd need
another cell or two for them.
Resistors under 1K are certainly not uncommon - I think I've got a few
values under 10 ohms in my stock at work (although I'll admit that I
don't use such low values very often.)
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca |
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Mark Jerde
Guest
|
| Posted:
Sat Nov 12, 2005 9:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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"tempus fugit" <toccata@no.spam.ciaccess.com> wrote in message
news:394ed$437555bd$d1d89e76$21351@PRIMUS.CA...
| Quote: | If you need that much quantity, don't go to RadioShack. Check out
www.mouser.com - they are WAY cheaper and have no minimum.
|
Thanks for the link. The last time I did any serious soldering the 80186
and 80286 were brand new. ;-)
-- Mark |
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Randy Day
Guest
|
| Posted:
Sat Nov 12, 2005 9:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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|
[piggybacking - for some reason Mark's reply didn't
show up here...]
| Quote: | I'm just back from Radio Shack with a package of these to get started
thinking:
http://www.radioshack.com/product/index.jsp?productId=2062588&cp
20 assorted LEDs, 2 - 3V, 10-20 mA
(They were the only thing economical. Other LEDs were one or two per
package, $1.98 to $4.98. I'll get another package when I go to get the
battery holder & resistors.)
Am I reading the specs right to use Vcc = 3 V, Vled = 2.5 V and Iled = 15
mA?
R = (3 - 2.5) / 0.015
= 33.33 Ohms
|
Since they are assorted LED's, I think you can
count on using 'assorted' values for the resistors.
Try finding a set of resistors from 47 ohm to maybe
150 ohm. Test each LED with the higher value
resistors and step down until a reasonable
brightness is achieved.
| Quote: | When I did electronics many years ago most of the resistors were in the
kiloohm and megaohm range. 33 ohms seems wrong. Am I missing something?
|
Nope, because you're dropping such a low voltage
(0.5 volts) at such a low current (.015 A).
A Vled of 2.5v just seems a bit high to me,
though; I'd suggest using 2v in your calcs.
You can always step down to a lower ohms
value if an LED is visibly dim. |
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The_Truth
Guest
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| Posted:
Sat Nov 12, 2005 9:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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alright... for radioshack green led's...
http://www.radioshack.com/product/index.jsp?parentPage=family&pg=2&cp=2032058.2032233.2032298&productId=2062572&tab=techSpecs
Typical MCD: 620 30 mA current (max.) Typical wavelength: 570mm Size:
T-1-3/4 (5mm) Viewing angle: 12° Sold in package of 1 Typical voltage:
2.1V, with a maximum of 2.8V
chances of running 30 led's from 1 nine volt are slim to none... at
least not for very long... you could put 2-3 nine volt batteries in
parallel... and that would divide the current draw between them...
ya know... i'm not big on radioshack prices... so i found a nice little
place...:-D
http://www.marktechopto.com/
can't get them all at once.. but free is a good thing... |
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Mark Jerde
Guest
|
| Posted:
Sat Nov 12, 2005 9:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
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|
Peter --
| Quote: | Am I reading the specs right to use Vcc = 3 V, Vled = 2.5 V and Iled = 15
mA?
R = (3 - 2.5) / 0.015
= 33.33 Ohms
When I did electronics many years ago most of the resistors were in the
kiloohm and megaohm range. 33 ohms seems wrong. Am I missing something?
Resistors under 1K are certainly not uncommon - I think I've got a few
values under 10 ohms in my stock at work (although I'll admit that I
don't use such low values very often.)
|
So I didn't make some kind of math error. Thanks.
-- Mark |
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Ken Moffett
Guest
|
| Posted:
Sat Nov 12, 2005 4:41 pm Post subject:
Re: Help Getting Started - Simple DC Circuit |
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|
a0196457@yahoo.com wrote in news:1131754310.567035.183770
@f14g2000cwb.googlegroups.com:
| Quote: | You will want to make sure the source voltage is a greater than the
led's forward voltage and the current limit resistor voltage drop. I
think white Leds are about 3V and Red Leds are 1.7V, but be sure to
check.
David
|
Check this URL for the Vf of different colored LED's:
http://www.oksolar.com/led/led_color_chart.htm |
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ehsjr
Guest
|
| Posted:
Sat Nov 12, 2005 5:35 pm Post subject:
Re: Help Getting Started - Simple DC Circuit |
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|
Mark Jerde wrote:
| Quote: | (I apologize for posting this basic circuit question. 25 years ago in
college I had to know E=IR etc. Just having problems getting started...)
I'm trying to "invent" a mechanical device. I've been having some alignment
problems with it and this afternoon it occured to me some simple electronics
would help a lot. But it has been many years since I've done anything more
complicated with electronics than change batteries in the household smoke
detectors. ;-) I'm looking at the Jameco web site, seeing if I can find
enough info to play with E=IR but there are just too many options &
choices...
I want to go to my neighborhood Radio Shack and buy
- 30 ea SPST NO switches
- 30 ea green LEDs
- 30 (?) ea resistors to limit current to the LEDs
- A circuit board to solder the LEDs & resistors to
- A battery case (e.g. 4 "D" cells) or 9v clip
I have an electronics soldering iron and plenty of wire.
The goal: When everything is lined up right on my mechanical device, all
the switches will be closed and all 30 LEDs will be glowing. Then I'll
unplug the battery, as the machine is ok once all the switches are closed.
(E.g., no long-term lighting requirement.)
How can I get started with this? For the battery which value to use, 1.5,
3, 6 or 9 volts? Does each LED need its own resistor or is one resistor
enough? (I don't care how bright the LEDs are so long as they are visible.)
Thanks.
-- Mark
|
Radio Shack is far too expensive for toggle switches, as you
discovered. You can get them for 40 cents each in lost of 10
from Allelectronics - http://www.allelectronics.com/
catalog # MTS-75PC
You can add the 31st LED and a simple circuit to tell you
when the other 30 LEDs are lit. That way, you need glance at
only 1 LED to see if all the others are on instead of needing
to look at all 30 of them. You'll need 30 diodes - catalog #
1N914TR (100 for $2.00) an NPN transistor (any NPN would work -
catalog # PN2222A is a suggestion) and a couple of resistors.
The single LED can serve as a "run" light. When it is lit, the
battery must not be disconnected. When it goes out, the battery
can be disconnected. (You could use it as the basis of an
automatic battery disconnecting circuit if you want.)
Here's the circuit:
+3 ---+------------------} }----+--------------------+
| | |
[LED1] [LEDn] [LED31]
| | |
[R1] [Rn] [R31]
| ->|- | ->|- |
+---[Diode1]---+ +---[DiodeN]---+ |
| | | | |
[Switch1] | [SwitchN] | |
| | | | |
Gnd | Gnd | |
| | |
+---} }-------------------+ |
| |
[4.7K] |
| /c
+----| NPN
| \e
[100K] |
| |
+-----+
|
Gnd
Use 100 ohm resistors for R1 through R31 and a 3 volt supply.
(If you don't want to use batteries, you could use catalog #
DCTX-330, which is a 3 volt 300 mA wall wart power supply.)
That will limit current through each LED to about 10 mA,
which is plenty bright enough for red LEDs. Catalog # LED-1
gets you 10 standard red LEDs for $1.00. The catalog numbers
for the resistors are 100-1/4 (100 ohm, 1/4 watt), 4.7K-1/4
and 100K-1/4 They cost 50 cents for 10 and must be ordered
in lots of 10.
Ed |
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Peter Bennett
Guest
|
| Posted:
Sun Nov 13, 2005 1:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
|
|
On Fri, 11 Nov 2005 21:45:50 GMT, "Mark Jerde"
<MarkJerde@newsgroup.nospam> wrote:
| Quote: | The goal: When everything is lined up right on my mechanical device, all
the switches will be closed and all 30 LEDs will be glowing. Then I'll
unplug the battery, as the machine is ok once all the switches are closed.
(E.g., no long-term lighting requirement.)
|
Just a thought - it is much easier to see one lit LED among many unlit
ones than it is to see one unlit LED among a bunch of lit ones, so I'd
wire the thing so that all lights are out when things are all properly
aligned. Also, if you do it this way, there is no need to remove the
battery while running the machine, and you will get a warning if
anything does slip out of alignment when it shouldn't. You would,
however, want to remove or switch off the battery while the thing is
disassembled.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca |
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Jasen Betts
Guest
|
| Posted:
Mon Nov 14, 2005 3:30 pm Post subject:
Re: Help Getting Started - Simple DC Circuit |
|
|
On 2005-11-12, ehsjr <ehsjr@bellatlantic.net> wrote:
| Quote: | Mark Jerde wrote:
(I apologize for posting this basic circuit question. 25 years ago in
college I had to know E=IR etc. Just having problems getting started...)
I'm trying to "invent" a mechanical device. I've been having some alignment
problems with it and this afternoon it occured to me some simple electronics
would help a lot. But it has been many years since I've done anything more
complicated with electronics than change batteries in the household smoke
detectors. ;-) I'm looking at the Jameco web site, seeing if I can find
enough info to play with E=IR but there are just too many options &
choices...
I want to go to my neighborhood Radio Shack and buy
- 30 ea SPST NO switches
- 30 ea green LEDs
- 30 (?) ea resistors to limit current to the LEDs
- A circuit board to solder the LEDs & resistors to
- A battery case (e.g. 4 "D" cells) or 9v clip
I have an electronics soldering iron and plenty of wire.
The goal: When everything is lined up right on my mechanical device, all
the switches will be closed and all 30 LEDs will be glowing. Then I'll
unplug the battery, as the machine is ok once all the switches are closed.
(E.g., no long-term lighting requirement.)
How can I get started with this? For the battery which value to use, 1.5,
3, 6 or 9 volts? Does each LED need its own resistor or is one resistor
enough? (I don't care how bright the LEDs are so long as they are visible.)
Thanks.
-- Mark
Radio Shack is far too expensive for toggle switches, as you
discovered. You can get them for 40 cents each in lost of 10
from Allelectronics - http://www.allelectronics.com/
catalog # MTS-75PC
You can add the 31st LED and a simple circuit to tell you
when the other 30 LEDs are lit. That way, you need glance at
only 1 LED to see if all the others are on instead of needing
to look at all 30 of them. You'll need 30 diodes - catalog #
1N914TR (100 for $2.00) an NPN transistor (any NPN would work -
catalog # PN2222A is a suggestion) and a couple of resistors.
The single LED can serve as a "run" light. When it is lit, the
battery must not be disconnected. When it goes out, the battery
can be disconnected. (You could use it as the basis of an
automatic battery disconnecting circuit if you want.)
Here's the circuit:
+3 ---+------------------} }----+--------------------+
| | |
[LED1] [LEDn] [LED31]
| | |
[R1] [Rn] [R31]
| ->|- | ->|- |
+---[Diode1]---+ +---[DiodeN]---+ |
| | | | |
[Switch1] | [SwitchN] | |
| | | | |
Gnd | Gnd | |
| | |
+---} }-------------------+ |
| |
[4.7K] |
| /c
+----| NPN
| \e
[100K] |
| |
+-----+
|
Gnd
|
you're pushing the envelope there...
with a 3.0V supply and a 1.7V led drop (typical for green LEDs) and a 0.6V
drop in the diode and in the be junction of the transiistor there's only 0.1V
left through 4.7K that's about 20uA at 0.6v the 100K will pass 6uA leaving 14
to flow into the base of the transistor.
unless that pn2222 has an hfE around 500 that last LED could be pretty dim.
and that's assuming 0.6V Vbe is sufficient
sticking a 1K resistor in parallel with each LEDn-Rn pair would be one
way to fix that.
Bye.
Jasen |
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Mark Jerde
Guest
|
| Posted:
Tue Nov 15, 2005 1:35 am Post subject:
Re: Help Getting Started - Simple DC Circuit |
|
|
Ed --
| Quote: | Radio Shack is far too expensive for toggle switches, as you
discovered. You can get them for 40 cents each in lost of 10
from Allelectronics - http://www.allelectronics.com/
catalog # MTS-75PC
|
Thanks.
| Quote: |
You can add the 31st LED and a simple circuit to tell you
when the other 30 LEDs are lit.
|
Wow, great idea. Thanks!
-- Mark |
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