Driving an LED through RC circuit(RC time constant)

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SUMMARY

The discussion focuses on designing an RC circuit to control the duration an LED remains lit in response to a 10 microsecond pulse signal from a 74HCT04 buffer. The user, Hary, seeks guidance on the circuit design, specifically on the placement of the RC components and the calculation of resistance (R) and capacitance (C) values. A recommended approach includes buffering the pulse, using a diode to charge a capacitor, and employing a Schmitt trigger gate to ensure stable LED operation. The Schmitt trigger is essential for preventing false triggering due to noise in the signal.

PREREQUISITES
  • Understanding of RC time constant in circuits
  • Familiarity with 74HCT04 buffer specifications
  • Knowledge of Schmitt trigger functionality
  • Basic principles of LED operation and circuit design
NEXT STEPS
  • Research how to calculate RC time constant values for desired LED duration
  • Learn about Schmitt trigger circuits and their applications in signal processing
  • Explore diode selection and its role in charging capacitors in RC circuits
  • Investigate practical circuit design techniques for LED drivers
USEFUL FOR

Electronics enthusiasts, circuit designers, and hobbyists interested in LED control and timing circuits will benefit from this discussion.

hary536
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Hi, i am trying to design a circuit, where i am trying to light up an LED long enough based on my pulse signal.
Here is what i am trying to do.

a 10us pulse(every second) --->74HCT04 buffer---> (RC circuit)----> LED.

since this is a 10us pulse, i want to make sure to light up the led for long enough time, so that one can see it. So i am trying to use RC time constant to add delay so that the LED remains ON for a longer time. I am not able to figure out the exact circuit for that and how i should design the RC circuit and how and where to place it with/before/after the LED.
Also i am not able to figure out how to calculate R and C.

It would be great, if someone can help me out.
Any kind of input is appreciated.
Thanks,
Hary.
 
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Traditionally, you'd buffer the pulse, drive through a diode into a cap (with parallel bleed resistor to give the RC time constant), and follow that with a Schmidtt trigger gate to drive the LED.

Quiz Question -- why does the second gate need to have a Schmidtt trigger input?
 

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