Comparator Question

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kucster

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I designed a simple circuit in multisim, all it does is have 4 lights stay solid and 3 lights flash, and when there respective switch is turned off the light turns off. I did the flashing by using a 555 timer to get a pulse and a comparator to clean it up. I used a virtual comparator in Multisim and I purchased a LM339N from radio shack, but it doesn't work. I tried it in Multisim and it doesn't work in there either. I don't understand what I'm doing wrong. Any help would be greatly appreciated.
Thanks
Sean
 

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You have the non-inverting input to the comparator tied to the positive rail. Put it on a voltage divider: two equal-value resistors (say 10K) in series from +12V to ground, use the tap in the middle to go to the comparator.
 
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I tried as you suggested and it still doesn't work. I'm including an updated schematic to see if I'm doing something wrong. Thank you so much for your help.
 

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Oh, sorry - you have TWO problems.

The second one is that the LM339 is open-collector. That chip can't drive "high". Connect the tops of those LED's to +12V. Connect the bottom of S3,5,7 to the output, pin 2.
 
Thank you so much for your help I really appreciate it. I've tried what you suggested and the light seems to just stay solid not blink, please see attached schematic. Am I using the wrong comparator? is there a better one I could use? I'm only trying to make the 3 leds flash, is there a better way of doing this?
Thanks
 

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That should work...

...but the blink rate is several hundred Hz. Did you check it on a scope? Increase C1 to about 100µf to slow it down enough to watch it blink.
 
I think you should look at the datasheet of the wimpy LM339 quad or the LM393 dual low power comparator IC. Its output current is a minimum of only 6mA.
But your LEDs have a current of 40mA for each string which is a total of 280mA so no wonder the circuit does not work.

You need an output transistor to drive all those LEDs.
 
Ouch. Thank you, Mr. Duck.

He's right, kucster - that thing isn't rated for enough collector current to drive a crummy LED.
 
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comparator and 7 segment disp.

HeLLo. does any1 knows how the comparator will work with the two 7 segment disp?..
The goal here is to establish a comparison between the two segments.. A LED will lit up either >, <, or =.. e.g. 1 and 2 are displayed, then automatically a < led will lit up.. HELP HELP HELP! any1 will be appr8d..
 

I think you need to

A calm down
B start a new thread
C write in plain english
 
You should try exploring the user interface a little before you ask questions... You simply enter the sub forum you want to post in and there's a large button in the upper left hand corner that says "New Thread" Click it, and provide details.
 
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