Need help/suggestions for Pulsing LED

[Tjordan5]

Hello all,

I am trying to build a simple circuit that will pulse an LED diode with a specific current at a specific frequency. I am currently trying to use a 555 with a resistor feedback loop.

The circuit begins at the Labview Wave Generator which sends a signal through a resistor. The pulse then splits the pulse to the input of the 555 and the feedback resistor which recombine on the output side and proceed through another resistor into the diode. I am using a 9V battery as the VDD and GND.


Currently it will pulse at the correct frequency, but I can't seem to get the correct current out.

Please let me know if you can help with this circuit or if you can suggest a better circuit to achieve my goal.

Thank you

[pebe]

With R7 and R10 both being equal, you have a unity gain amplifier. So the output voltage will be 1V RMS. But the voltage drop across a LED is typically 2V, so that's not enough to drive it.

If you increase R10 to 4K7 then you will get an output of 4.7V. Then you will have 2.7V dropped across R1, so a resistor of 220ohms will give you a 12mA drive.

Alternatively, you could drive the led with the square wave from a 555, and the circuit would be simpler with only one battery. I'll give you a circuit if you say what frequency you want.