Why wont this work - 555 problems

170

03:15:19

This works perfectly on my breadboard. Why not here?

When the switch is closed, the 555 should provide power on pin3 to charge the capacitor for the trigger. It also lights the LED. When the button is pushed, the voltage rise on the threshold pin should drive pin3 to ground, turning off the light until the voltage on the trigger drops back down to 3V. At this time pin3 outputs power again and relights the LED. 

At least that's how it works on my bench.

published 9 years ago

rich11292000

9 years ago

I added a opened switch on pin 3 said voltage source is shorted. It only happened once.

2ctiby

9 years ago

I have made some adjustments.....hope it is what you are looking for: http://everycircuit.com/circuit/6456931195027456

psteichen

9 years ago

2ctiby: Thanks! This accomplished the same thing, and now it works on my breadboard and in EC minus the diode. I appreciate your help!

hurz

9 years ago

If you do not short circuit the discharge pin7 and do not overload output port pin3, than its working fine.

psteichen

9 years ago

Hurz: Thanks, that works too. Placed a small resistor on pins 3 & 7. Is this necessary in real life though. I thought the 555 is internally limited throughout it's operating voltage range, so that resistors are unnecessary?

hurz

9 years ago

Integrated circuit designs are mostly current orientated. That mean for example the maximum current at pin7 will have even for short to Vcc a limit and wont damage the 555. Anyway, i would not connect it to Vcc because its waste of current and does heat up the overall maximum of 555 power dissipation.

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