Hello AAC forum,
Have breadboarded and PCB'd the venerable 555 for several
different set ups. Used the 555 in mono stable mode as a
delay on and delay off timer. And have employed it in astable
mode as a oscilator to clock a 4017 decade counter at 1 hz and
in the audible range, 440 hz to produce a beep.
Found a variation of the astable that is supposed to pulse quickly
and slow down until it stops.
http://www.doctronics.co.uk/555.htm#astable
Have found another version at
http://en.wikibooks.org/wiki/Practical_Electronics/Astable/Diminishing_Frequency
Have bread boarded both of these with little or no luck.
So I tried reworking the schematic from Practical Electronics to make it simpler.
This only served to reinforce that except for the 47uF capacitor between source and
ground, called a decoupling cap, the two circuits are virtually identical.
Have tried changing out the IC and have bread boarded both several times.
Also have tried with and with out the grounding cap from pin 5.
What happens is first the indicator LED comes on before the momentary
normally off switch is engaged which was not expected. Then sometimes the LED
stays on after the switch is pressed and sometimes it will blink once after a s
econd or two and stays on indefinitely.
Started over from scratch a fifth time and tried the breadboard version shown
in the Doctronics site but is hard to read so did a fritz of the board as I
laid it out.
Beginning to think there is something wrong with the design.
Any ideas?
Thanks.
Allen in Dallas
Have breadboarded and PCB'd the venerable 555 for several
different set ups. Used the 555 in mono stable mode as a
delay on and delay off timer. And have employed it in astable
mode as a oscilator to clock a 4017 decade counter at 1 hz and
in the audible range, 440 hz to produce a beep.
Found a variation of the astable that is supposed to pulse quickly
and slow down until it stops.
http://www.doctronics.co.uk/555.htm#astable
Have found another version at
http://en.wikibooks.org/wiki/Practical_Electronics/Astable/Diminishing_Frequency
Have bread boarded both of these with little or no luck.
So I tried reworking the schematic from Practical Electronics to make it simpler.
This only served to reinforce that except for the 47uF capacitor between source and
ground, called a decoupling cap, the two circuits are virtually identical.
Have tried changing out the IC and have bread boarded both several times.
Also have tried with and with out the grounding cap from pin 5.
What happens is first the indicator LED comes on before the momentary
normally off switch is engaged which was not expected. Then sometimes the LED
stays on after the switch is pressed and sometimes it will blink once after a s
econd or two and stays on indefinitely.
Started over from scratch a fifth time and tried the breadboard version shown
in the Doctronics site but is hard to read so did a fritz of the board as I
laid it out.
Beginning to think there is something wrong with the design.
Any ideas?
Thanks.
Allen in Dallas