FAQFAQ   GalleryGallery   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in   Forum RSS Feed   Hacked Gadgets Main Site 

Need Help with resistors
Goto page Previous  1, 2, 3, 4, 5  Next
 
Post new topic   Reply to topic    Hacked Gadgets Forum Index -> LED Projects
View previous topic :: View next topic  
Author Message
Guest
Guest





PostPosted: Fri Jul 21, 2006 9:43 am    Post subject: Reply with quote

Thanks guys, you're the best!!!
Back to top

Guest
Guest





PostPosted: Sat Jul 29, 2006 9:49 am    Post subject: Question Reply with quote

I'm assuming that the LED is using a voltage of 3.2V (what I've foound on avg) with a current of 20mA. Calculating for R using R=V/I gives you something like 225-270 ohms for the resistor...So I'm trying to figure out why a 470K ohm resistor is being used. It seems to me that would be too much resistance on the circuit and would cut it doen well below the supply voltage needed for the LED.

And why is the transistor in the circuit? I thought they were used for switches or transformers?
Back to top
Guest
Guest





PostPosted: Sat Jul 29, 2006 10:54 am    Post subject: Answered my own question re:last post Reply with quote

Ok, going through some other posts on this site I found out why the 470ohm resistor was used, to balance out the battery usage. A 220 ohm R could have been used and I assume it would have been brighter.

My question here still is why the transistor was used in this circuit?
Back to top
Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sat Jul 29, 2006 1:00 pm    Post subject: Re: Answered my own question re:last post Reply with quote

Guest wrote:
Ok, going through some other posts on this site I found out why the 470ohm resistor was used, to balance out the battery usage. A 220 ohm R could have been used and I assume it would have been brighter.

My question here still is why the transistor was used in this circuit?


Correct the 470 ohm was used to conserve battery power. The transistor is used to provide the current needed.
Back to top
View user's profile Send private message Send e-mail
Guest
Guest





PostPosted: Sat Jul 29, 2006 2:39 pm    Post subject: RE: current Reply with quote

The LED will draw as much current as needed as long as the voltage supplied is correct, which you have done with the 470ohm resistor, dropping the voltage down from 9V to V(LED). And the LED is only going to require 20-30mA of current, which the 9V battery is more than able to supply for quite a while. Are you saying that the introduction of the photoresistor requires a greater amount of current?

Since the 9V battery is already supplying the correct voltage because the uneeded portion is being dropped across the resistor, what use is the transistor?

I would be happy to find this answer in other forums if you'd rather not go into it, just found someone that responds so I'm asking Wink Thanks, by the way Very Happy
Back to top
Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sat Jul 29, 2006 2:51 pm    Post subject: Re: RE: current Reply with quote

Guest wrote:
The LED will draw as much current as needed as long as the voltage supplied is correct, which you have done with the 470ohm resistor, dropping the voltage down from 9V to V(LED). And the LED is only going to require 20-30mA of current, which the 9V battery is more than able to supply for quite a while. Are you saying that the introduction of the photoresistor requires a greater amount of current?

Since the 9V battery is already supplying the correct voltage because the uneeded portion is being dropped across the resistor, what use is the transistor?

I would be happy to find this answer in other forums if you'd rather not go into it, just found someone that responds so I'm asking Wink Thanks, by the way Very Happy


The transistor is being used since the photocell would not be able to handle the current to drive an LED directly. The transistor is also being used here to turn on the LED properly (on when dark).

If the photocell could handle the current, its resistance increases as it gets dark. This would cause the light to go on in bright light and off in darkness.
Back to top
View user's profile Send private message Send e-mail
bjia52
Guest





PostPosted: Mon Sep 18, 2006 2:56 pm    Post subject: Reply with quote

Thanks for all you guys help. I'm new to this field and trying to make it more fun and need help from you guys a lot. Thanks again for all you info.
What if I want to set the timer on this? Says 1 to 2 hours to have it on after dark or turn itself off after on for 2 hours or more. Is there anything we can do?
Thanks
Back to top
Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Mon Sep 18, 2006 5:00 pm    Post subject: Reply with quote

bjia52 wrote:
Thanks for all you guys help. I'm new to this field and trying to make it more fun and need help from you guys a lot. Thanks again for all you info.
What if I want to set the timer on this? Says 1 to 2 hours to have it on after dark or turn itself off after on for 2 hours or more. Is there anything we can do?
Thanks


It would be possible to do this by adding some extra electronics. A microcontroller such as a PIC 16F628A would work but is overkill for this simple application. You might want to look into using a 555 timer in its "one shot" mode. Here is a site with some information to get you started:
http://www.uoguelph.ca/~antoon/gadgets/555/555.html
Back to top
View user's profile Send private message Send e-mail
ust2010
Newbie


Joined: 26 Nov 2006
Posts: 2

PostPosted: Sun Nov 26, 2006 8:28 pm    Post subject: Reply with quote

I dont know how to read wiring diagrams so please just tell me what connects to what. or someone make a a very simple diagram. I want to use a normal switch to turn the light on and off not that auto switch thing or the photo thing. does that mean I can just connect the 470ohm resistor to the positive side of the batt and the other side to the switch to the negative side?
Back to top
View user's profile Send private message
Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Mon Nov 27, 2006 6:50 pm    Post subject: Reply with quote

ust2010 wrote:
I dont know how to read wiring diagrams so please just tell me what connects to what. or someone make a a very simple diagram. I want to use a normal switch to turn the light on and off not that auto switch thing or the photo thing. does that mean I can just connect the 470ohm resistor to the positive side of the batt and the other side to the switch to the negative side?


Hi ust2010,

Yes, just go from the positive of the battery connector (red wire) to the resistor, from the other end of the resistor to the long lead of the LED, from the short lead of the LED to the stitch and finally from the other terminal on the switch to negative of the battery.

Alan
Back to top
View user's profile Send private message Send e-mail
ust2010
Newbie


Joined: 26 Nov 2006
Posts: 2

PostPosted: Mon Nov 27, 2006 7:29 pm    Post subject: Reply with quote

Sweet, I got it working so i'm making a buch using a Grey goose bottle and other alc bottles. I noticed that some LED's dont need resistors and get really bright. some are dimmer without a resistor, and some dont work at all without a resistor.
Back to top
View user's profile Send private message
Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Mon Nov 27, 2006 8:26 pm    Post subject: Reply with quote

ust2010 wrote:
Sweet, I got it working so i'm making a buch using a Grey goose bottle and other alc bottles. I noticed that some LED's dont need resistors and get really bright. some are dimmer without a resistor, and some dont work at all without a resistor.


Sounds like a cool project Smile

I would use resistors on all LEDs, many can take it for some time but you are sure to reduce their life.

Use a resistor calculator to calculate the correct value.

http://alan-parekh.com/led_resistor_calculator.html
Back to top
View user's profile Send private message Send e-mail
cklehe
Newbie


Joined: 11 Jan 2009
Posts: 1

PostPosted: Sun Jan 11, 2009 4:19 pm    Post subject: help Reply with quote

Hi alan, it looks like all those conversations are pretty old, but i just finished doing my own circuit inspired from your diagram and i have a problem.
When i plugged the battery 9V, it worked just fine for 30 seconds, off switch was off, allways on, on, auto worked too; then off was allways on and auto didn't respond to light anymore, anyhow everything was allways on.
Why? Is it my transistor that blew/flattened up??? i suppose, i don't think there is any bridge i soldered everything pretty appart (used three wires to connect everything to the B so that it will be far away from E and C in the transistor...)
Help? i don't get it.
To sumarize i have a 9V battery, two rgb leds 3.3v 20ma with a 150ohm resistance before. A 10k resistance in place of the 1K, a 10k variable resistor in place of the 100k, A C33725 transistor and a LDR...
If the transistor blew up what should i do buy a bigger one, change the resitance... help i am a newbee at electronics.
Back to top
View user's profile Send private message
Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sun Jan 11, 2009 11:58 pm    Post subject: Re: help Reply with quote

cklehe wrote:
Hi alan, it looks like all those conversations are pretty old, but i just finished doing my own circuit inspired from your diagram and i have a problem.
When i plugged the battery 9V, it worked just fine for 30 seconds, off switch was off, allways on, on, auto worked too; then off was allways on and auto didn't respond to light anymore, anyhow everything was allways on.
Why? Is it my transistor that blew/flattened up??? i suppose, i don't think there is any bridge i soldered everything pretty appart (used three wires to connect everything to the B so that it will be far away from E and C in the transistor...)
Help? i don't get it.
To sumarize i have a 9V battery, two rgb leds 3.3v 20ma with a 150ohm resistance before. A 10k resistance in place of the 1K, a 10k variable resistor in place of the 100k, A C33725 transistor and a LDR...
If the transistor blew up what should i do buy a bigger one, change the resitance... help i am a newbee at electronics.


Is the switch operating as it should. What it is doing is connecting either the 100K or the 1K to the 9 volt source. When you do this yourself not using the switch does the device heat up? What made you want to change the resistor values? Did it work with the values that are on the schematic? If you can please measure the base current and the collector current when the device is hot.
Back to top
View user's profile Send private message Send e-mail
electron
Semi Newbie


Joined: 30 Mar 2009
Posts: 8
Location: UK

PostPosted: Mon Mar 30, 2009 3:38 am    Post subject: Reply with quote

Hi
I am a newbie to this forum. I have been playing around with electronics since just after WW2. Those were the days when you could buy tubes for next to nothing. 6L6, 6v6, 5v4, and so it goes on. Now with solid state its a whole new ball game. I am certain I am going to enjoy myself here. I took up photography a few years back and have made a few gizmo`s to aid this. Cool
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    Hacked Gadgets Forum Index -> LED Projects All times are GMT - 6 Hours
Goto page Previous  1, 2, 3, 4, 5  Next
Page 4 of 5

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum



Powered by phpBB © 2001, 2005 phpBB Group