LED is not flashing using 555

popkutty said:

Ya, how's it happening.? By this, we can do touch sensor I think...

Click to expand...

you might need some other circuits if u want build a touch sensor because the output will turn off when you take your finger off it.

ericgibbs said:

hi,
Try this very simple layout, as I said earlier the 555 maybe faulty.!

Click to expand...

eric, i built the circuit you drew,but why is the LED keep staying ON? i mean it blinks but it keep staying and turns off for a second and on again.., i thought it would stay off and turn on after a limited time(as capacitor value).. U got what i meant?

Ziddik said:

eric, i built the circuit you drew,but why is the LED keep staying ON? i mean it blinks but it keep staying and turns off for a second and on again.., i thought it would stay off and turn on after a limited time(as capacitor value).. U got what i meant?

Click to expand...

hi Z,
Its an Astable [oscillator] so it will flash On/Off at a slow rate.. the 10K/1K and 100uF set the ON and OFF periods, 10 times longer ON than OFF [ approx]

popkutty said:

Ya, how's it happening.? By this, we can do touch sensor I think...

Click to expand...

Yes, you can trigger a 555 timer simply by touching pin 2. Here is a touch sensor circuit for the 555. The timer is wired as a one-shot (monostable), and the value of the capacitor and resistor control how long the output stays on after you let go:

**broken link removed**

You can also add another 555 timer to make a bistable switch, which keeps the output on indefinitely when you touch the trigger and then let go:



Also, if you want a touch-on-touch-off, you can add in a 7474 flip-flop:



If you're interested in making a touch switch, here are a few ideas to go on.

I hope this helps!
Regards,
Der Strom

EDIT: In these circuits, it also couldn't hurt to have a pull-up resistor connected to pin 2 as well. This will prevent false triggering. 100K-500K should be good, but feel free to experiment a bit.

I think I got answer for Ziddik, Here is the calculation, The output's High and Low in second can be calculated from here..
http://www.simple-electronics.com/search/label/555 timer calculator
Am I right Eric?

popkutty said:

I think I got answer for Ziddik, Here is the calculation, The output's High and Low in second can be calculated from here..
http://www.simple-electronics.com/search/label/555 timer calculator
Am I right Eric?

Click to expand...

hi,
Download this and install as explained... you can make all the basic 555 circuits in simulation
https://www.electro-tech-online.com/blogs/ericgibbs/125-simple-7555-cmos-timer-calculator-v1-2.html