LEDS and the 555
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Posted by John Fields on June 11, 2005, 10:11 pm
Please log in for more thread options On Sat, 11 Jun 2005 17:25:37 -0400, Randy Joseph --- It sounds to me like you may have a wiring error. How do you have the 555 hooked up? -- John Fields Professional Circuit Designer | |||||||||||||||||||||||||||||||||||||
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Posted by Lyle on June 6, 2005, 7:40 pm
Please log in for more thread options Ironically, I just finished a version of this using a 556 this weekend for IR LED's. You probably already know this but the voltage drop across a regular LED is pretty large, I think my reds were 3.7 volts (while the IR's are only 1.3 volts) and the 555 output as a current source drops atleast 1 volt from 5-15 v Vcc with currents from 15-100 mA. So the 9 volt battery puts out 9.3 volts but the current limiting resistor only drops 4.6 volts, so your current calculations may be double the actual current. See the previous post "voltage drop from a 555/556". The standard 555 has a max rated output of about 150 mA if I remember correctly. I bought the 556-CN for a few cents more which has a rated max continuous output of 1.6 A! I've used them to drive 1A on several occasions reliably, I try not to push harder than 50% max for most things. Lastly, the lens at the end of LED's varies tremendously from model to model. This is useful as some applications require a spread beam while others require a tight beam. So the LED with the spread beam looks dimmer but actually puts out the same total amount of light. good luck Lyle (just a hobbyist) >I am designing a project for a freind of mine and I am making 3 LEDS
> blink at at 3 different rates. I am using 555's to do this. The > problem I am having is the LEDS are not bright enough when I drive > them with the 555 directly. I have used high brigtness LEDS and they > are a little brighter but not bright enough. I am using 9 vdc and > fiquirng 20ma to run the LEDS. When I drive them directly without the > 555's they are plenty bright enough. My question is how do I get the > LEDS brighter. Is there a driver or something I can us. > > Your help is greatly appreciated. > > Thank you, > > Randy | |||||||||||||||||||||||||||||||||||||
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Posted by Quack on June 7, 2005, 3:18 am
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Hi Lyle, >Lastly, the lens at the end of LED's varies tremendously from model to
>model. This is useful as some applications require a spread beam while >others require a tight beam. So the LED with the spread beam looks dimmer >but actually puts out the same total amount of light. I have been looking for 'lensed led' suppliers for ages, i have seen led's in products that project a nice 'square' onto a surface 10cm away (although faint at that distance). I need to use them for 'aiming guides' for allignment of an optical device. I have asked many people about this, including posting here but everone just argues that they must be laser diodes. They are not, most curtainly they are LED's, i just cant find a supplier probably because i dont know what they are called exactly, any idea ? :) Alex. | |||||||||||||||||||||||||||||||||||||
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Posted by Don Klipstein on June 8, 2005, 5:20 am
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>
>>Lastly, the lens at the end of LED's varies tremendously from model to
>>model. This is useful as some applications require a spread beam while >>others require a tight beam. So the LED with the spread beam looks dimmer >>but actually puts out the same total amount of light. >
>I have been looking for 'lensed led' suppliers for ages, i have seen >led's in products that project a nice 'square' onto a surface 10cm away >(although faint at that distance). I need to use them for 'aiming >guides' for allignment of an optical device. > >I have asked many people about this, including posting here but everone >just argues that they must be laser diodes. They are not, most >curtainly they are LED's, i just cant find a supplier probably because >i dont know what they are called exactly, any idea ? :) These don't have special notation other than very narrow "viewing angle" around 8 degrees or less. And not all with "viewing angle" in the upper part of this range have nice square focused images of the "chip" (die). A few with such nice nice narrow focused beams even claim a much wider "viewing angle" as wide as 15 degrees for parts with bodies 5 mm in diameter and 30 degrees for parts with bodies 3 mm in diameter due to claiming the width of the image of the "die cup". - Don Klipstein (don@misty.com) | |||||||||||||||||||||||||||||||||||||
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Posted by Quack on June 8, 2005, 2:51 am
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> These don't have special notation other than very narrow "viewing angle"
>around 8 degrees or less. And not all with "viewing angle" in the upper >part of this range have nice square focused images of the "chip" (die). Thanks Don, thats interesting. Specifically the ones i have seen and want project only the outline of a square (not filled) with very little ambient light around that. Correct me if i am wrong, but i imagine the die would cast a solid 'filled' square by just using a narrow angle ? Alex. | |||||||||||||||||||||||||||||||||||||
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>me. I can get the LEDS to a usable brightness with the LED Driver
>circuit below it just when I hook it up the blinking stops of the 555
>and the led stays on all the time. I have no problems until I hook up
>the 2n4401. I must be missing something on the 555 though because
>when I measure the output of pin 3 I get a constant 7 volts and when
>I hook it up to the base of the 2N4401 it casues the transistor to
>stay on. The parts that is throwing me is the LED blinks without the
>2N4401 hooked up. Should not the output of pin 3 change states from 7V
>to roughly OV, is this not what casues the LED to turn on and off.
>This is not hapenning with my measurements.