Let's Make Robots!

555 chip and continuity

When I place probes on pin 1 and pin 8 of a 555 timer chip, should there be continuity?

I'm trying to put a circuit together, actually a circuit to test if a 555 is good or bad, and can not

seem to get it to work.  Wondering if the chip I'm trying to use is already bad....  


Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

along with trying to get the motor controller circuit working (the PWM approach), I've been trying to build this breadboard

which will test the 555 chip.  When you hook a 9 volt to it the LEDs are supposed to alternate blinking (if the chip is good).  I've only been able to get both LEDs to light up at the same time.  Attached is a link to the circuit I've been working with.  If you could take a look at it.... does it seem like it should work?  I guess maybe the next thing is I should upload a picture of my breadboard... kind of frustrating.... but thanks again.  Learning alot with this exercise... but still, frustating.


That circuit should work fine but try swapping C1 for a 10uF or even 100uF. You say both LEDs are on at once which indicates it may be working fine but just going too fast for you to see the LEDs turn off.

Are you using a CMOS or TTL 555 timer?

The TTL timer and sink / source about 200mA max.
The Cmos timer can sink 100mA, but can olny source 10mA which may not be enough and make both LEDs to appear on at once.

Pins 1 & 8 are the power pins. Trying to test if the chip is good by doing a continuity test on the power pins is pointless and it's possible you could damage the chip by doing this.


thanks very much for the replies, bdk6.  I spent most of yesterday afternoon and evening 

trying to get these circuits to work and no love.  I keep ripping the things apart and starting over :-(

I'll try your suggestion of swapping pin 3 for 7.... and I'll take a look at the link you provided.

Thanks, I appreciate the help.