basic circuit

[kdg007]

can anyone give me a basic circuit for modulating a single LED with a function generator and a voltage source ?????????

 

[Reloadron]

Depends on the function generator. If the function generator allows for a pulse out and allows adjusting the pulse width for a set frequency Then it becomes relatively easy. Let the function generator drive a transistor that drives the LED or if the function generator has a beefy enough current out let the function generator drive the LED directly. Depends on what you have?

Ron

 

[kdg007]

i have function generator...i know how to drive an LED with a transistor..but i want to do it without a transistor... bit confused how to do that..
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i want the function generator to drive the LED directly but is it possible to if the LED is given a DC supply ?
View attachment 65398
where to feed the function generator(with dc offset zero) in this circuit ?? :O

 

[Reloadron]

Replace the battery in your circuit with the function generator. You have a battery (Vsupply) of 5 volts. The LED Vf is 3.5 volts and you have a resistor 85 Ohms limiting the current to about 17 mA. Long as your function generator can source the needed current you would replace the battery with the function generator output. I do it all the time for checking optical tach pickup units. Now if you want to PWM the LED the function generator will need to allow adjusting the output pulse with at a set frequency.

Ron

 

[kdg007]

is there a possible way not to replace the battery and also keep function generator ?
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i can set the 5v with the dc offset ... i will do that now ans see..

 

[kdg007]

ok .. i replace the battery with the function generator...and i got the waveform across the LED...but how am i certain that the waveform i am seeing is the waveform from LED ????it can be from the function generator throught the resistor ???

 

[Reloadron]

The only way not to drive the LED directly with the function generator is using a transistor as mentioned earlier but you do not want to use a transistor. If you are curious as to what the waveform going to the LED actually looks like you would need a scope. The resistor serves to limit the LED current when you have a 5 volt pulse. All you have is a function generator driving a LED with a series resistor. Just like your circuit shows.

ok .. i replace the battery with the function generator...and i got the waveform across the LED...but how am i certain that the waveform i am seeing is the waveform from LED ????it can be from the function generator throught the resistor ???

I am not sure what you are asking?

Ron

 

[davenn]

ok .. i replace the battery with the function generator...and i got the waveform across the LED...but how am i certain that the waveform i am seeing is the waveform from LED ????it can be from the function generator throught the resistor ???

where else would it be from other than the function generator ? its the only signal source you have connected to the LED

As Ron said, a scope will show you what the signal looks like

Dave