555 timer help needed

Thread Starter

b3an

Joined Feb 12, 2024
15
I am trying to build a simple flashing led circuit with a NE555P, however I have ran into a problem of the LED just constantly staying on. I would appreciate at suggestions on fixing this. The current value I have at the moment are: Ra = 100k ohm, Rb = 470k ohm, Rl = 330 ohm, C = 1uF, and I have using a 9V battery to power the circuit.
IMG_2293.jpegIMG_2294.jpeg(battery not currently connected)
 

SamR

Joined Mar 19, 2019
5,048
I have ran into a problem of the LED just constantly staying on
LEDs can fool ya. Above ~25 flashes per second the do appear to be simply ON. Good time to put an oscilloscope on it and see just what it is actually doing.
 

dl324

Joined Mar 30, 2015
16,930
As noted, Rb is 470 ohms. That gives a frequency of 9.9Hz with a very high (LED on time) duty cycle. So you can't discern the off time.

1707838841598.png
 

crutschow

Joined Mar 14, 2008
34,455
It's good practice to measure the resistors with an ohmmeter before you connect them in the circuit, to be sure they are the value you intended.
 
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