I've been trying to make an LED blink. My first approaches were without the 555 timer, and they were unsuccessful. I decided to make an Astable multivibrator circuit. I'm using an NE555, and I'm using the circuit on this video. For R1, I used a 680ohm resistor, and for R2 I've used 1k, 10k, 100k, 500k, 1M ohm resistors, and none of them have proven succesful. For my capacitor, I'm using a 100uF capacitor. I've tried 1uF and 1000uF aswell. Please help!
Electronic – Very Basic 555 Timer oscillator not working
555ne555oscillator
Related Solutions
R1 should not be less than about 1K. Shorting it will do bad things, the discharge transistor internal to the 555 will be trying to short the power supply. The 555 may be damaged, and it will not work properly.
As Russell says, your 555 timer circuit looks a bit off. Search for 'astable 555 circuit' to get your square wave generated. There are online calculators to set the values of the resistors and capacitors.
To get 0.2Hz you will need about 50K for R1 and R2 and 47uF for C:
Now the reason that you are just seeing a flash when you changed to a MOSFET is that their gain is so high. So even if you are using your R1 and C1 to generate a ramp, the on/off voltage of the MOSFET is probably crossed immediately.
What you need instead is an NPN transistor that can handle the current that you need for your LEDS. Just find out how much current you are drawing for the LEDs and check the datasheet of the transistor to see if it will work.
Here's a circuit that I simulated that gives a pretty good ramp up and down at 20mA. Not sure how much current you need but that might be a pretty good start.
I used a 0.2Hz square wave instead of the 555 just for simplicity.
To slow down the ramp up/down time increase R1 or C1. Because R1 is connected to the base, this will also effect the brightness of the LED. So it might be better to choose a good value there first and then change C1 for the timing.
Best Answer
First of all, try following a schematic rather than a youtube tutorial showing a breadboard. There is a good chance you may have wired something incorrectly.
A 555 timer in an astable configuration would look like this:
simulate this circuit – Schematic created using CircuitLab
Using this, you should be able to place your components on a breadboard, following the schematic closely. I assume you know the internal connections of a breadboard, but just in case, here is a diagram:
If you change the values of R1/R2 or C1 then you will be able to vary the frequency. Or stick a potentiometer in the place of R2.
This link HERE will be able to help you calculate which values to use for your desired frequency.
If you wanted to work it out yourself, you could use the forumula:
f= 1.44/(R1+2R2)C
Although I have found that to be a tad off sometimes! But it gives you a ballpark idea as real world electronics will never be exact!
So, basically, take it apart and rebuild it, this time following a schematic!
P.S make sure you have a working LED!