LEDS and the 555
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Posted by Randy Joseph on June 6, 2005, 3:24 pm
Please log in for more thread options 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 John Fields on June 6, 2005, 3:02 pm
Please log in for more thread options On Mon, 06 Jun 2005 12:24:19 -0400, Randy Joseph --- There are a few things you can do: 1. Assuming that you're using the 555 to source current into the LED, Pull the 555's TRIGGER input to ground so that the LED stays lit all the time, then measure the output voltage at pin 3 and use that voltage to calculate the value of the current-limiting resistor. 2. If you're using the 555's output as a sink, do the same thing with the TRIGGER input pulled up to Vcc. 3. Or, do this: 9V | [330] | |A [LED] 555 | +-----+ C | OUT|---[3k]---B 2N4401 +-----+ E | GND -- John Fields Professional Circuit Designer | |||||||||||||||||||||||||||||||||||||
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Posted by Randy Joseph on June 7, 2005, 7:51 pm
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On Mon, 06 Jun 2005 12:02:38 -0500, John Fields >On Mon, 06 Jun 2005 12:24:19 -0400, Randy Joseph
> >>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. >
>--- >There are a few things you can do: > >1. Assuming that you're using the 555 to source current into the LED, > Pull the 555's TRIGGER input to ground so that the LED stays lit > all the time, then measure the output voltage at pin 3 and use that > voltage to calculate the value of the current-limiting resistor. > >2. If you're using the 555's output as a sink, do the same thing with > the TRIGGER input pulled up to Vcc. > > >3. Or, do this: > > 9V > | > [330] > | > |A > [LED] > 555 | > +-----+ C > | OUT|---[3k]---B 2N4401 > +-----+ E > | > GND I tried your 3rd option and the LED is bright enough but it stays on all the time when I remove the 3k resistor from the base it goes off. The timing circuit works well without the 2N4401 but like I said earlier its not bright enough. How do I get the 555 timing circuit to work again using the 2N4401. I think I am close but need a nudge. Thank you, Randy | |||||||||||||||||||||||||||||||||||||
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Posted by John Fields on June 7, 2005, 7:20 pm
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On Tue, 07 Jun 2005 16:51:23 -0400, Randy Joseph >On Mon, 06 Jun 2005 12:02:38 -0500, John Fields
> >>On Mon, 06 Jun 2005 12:24:19 -0400, Randy Joseph
>> >>>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. >>
>>--- >>There are a few things you can do: >> >>1. Assuming that you're using the 555 to source current into the LED, >> Pull the 555's TRIGGER input to ground so that the LED stays lit >> all the time, then measure the output voltage at pin 3 and use that >> voltage to calculate the value of the current-limiting resistor. >> >>2. If you're using the 555's output as a sink, do the same thing with >> the TRIGGER input pulled up to Vcc. >> >> >>3. Or, do this: >> >> 9V >> | >> [330] >> | >> |A >> [LED] >> 555 | >> +-----+ C >> | OUT|---[3k]---B 2N4401 >> +-----+ E >> | >> GND >
> >I tried your 3rd option and the LED is bright enough but it stays on >all the time when I remove the 3k resistor from the base it goes off. >The timing circuit works well without the 2N4401 but like I said >earlier its not bright enough. How do I get the 555 timing circuit to >work again using the 2N4401. I think I am close but need a nudge. 9V | [330] | |A [LED] 555 | +-----+ C | OUT|---[3k]-+--B 2N4401 +-----+ | E [1k] | | | GND GND -- John Fields Professional Circuit Designer | |||||||||||||||||||||||||||||||||||||
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Posted by Randy Joseph on June 11, 2005, 8:25 pm
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I am still having problems with this circuit. It has really thrown 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. Your help appreciated. Randy On Tue, 07 Jun 2005 16:20:07 -0500, John Fields >On Tue, 07 Jun 2005 16:51:23 -0400, Randy Joseph
> >>On Mon, 06 Jun 2005 12:02:38 -0500, John Fields
>> >>>On Mon, 06 Jun 2005 12:24:19 -0400, Randy Joseph
>>> >>>>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. >>> >>>--- >>>There are a few things you can do: >>> >>>1. Assuming that you're using the 555 to source current into the LED, >>> Pull the 555's TRIGGER input to ground so that the LED stays lit >>> all the time, then measure the output voltage at pin 3 and use that >>> voltage to calculate the value of the current-limiting resistor. >>> >>>2. If you're using the 555's output as a sink, do the same thing with >>> the TRIGGER input pulled up to Vcc. >>> >>> >>>3. Or, do this: >>> >>> 9V >>> | >>> [330] >>> | >>> |A >>> [LED] >>> 555 | >>> +-----+ C >>> | OUT|---[3k]---B 2N4401 >>> +-----+ E >>> | >>> GND >>
>> >>I tried your 3rd option and the LED is bright enough but it stays on >>all the time when I remove the 3k resistor from the base it goes off. >>The timing circuit works well without the 2N4401 but like I said >>earlier its not bright enough. How do I get the 555 timing circuit to >>work again using the 2N4401. I think I am close but need a nudge. >
> > 9V > | > [330] > | > |A > [LED] > 555 | > +-----+ C > | OUT|---[3k]-+--B 2N4401 > +-----+ | E > [1k] | > | | > GND GND | |||||||||||||||||||||||||||||||||||||
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>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.