multivibrator ringing ?

[Bazukaz]

Hi,
I have built this multivibrator :
http://www.interq.or.jp/japan/se-inoue/e_ckt5_1.htm

I wanted to use it to test amplifiers.But in scope , i see some small ringing at edges of square wave! I used 100nF supply bypass cap directly at ICs pins.PSU is regulated with 7805.there is no supply noise. I thought it was my error , so i built the same cirtuit again , but the problem remains.
How can this be fixed ?

Best regards,
Lukas.

[mzzj]

Originally posted by Bazukaz
Hi,
I have built this multivibrator :
http://www.interq.or.jp/japan/se-inoue/e_ckt5_1.htm

I wanted to use it to test amplifiers.But in scope , i see some small ringing at edges of square wave! I used 100nF supply bypass cap directly at ICs pins.PSU is regulated with 7805.there is no supply noise. I thought it was my error , so i built the same cirtuit again , but the problem remains.
How can this be fixed ?

Best regards,
Lukas.

Try better bypassing, for example remove that 100nF and use only 220uF electrolytic cap. and/or use cmos-version of 555, LMC555 for example.

And, have you calibrated your scope probes?

[Eva]

Either follow mzzj advice or solder the 100nF directly on the leads of the electrolytic. You have just discovered that 100nF decoupling capacitors are a two edged solution.

[clem_o]

Where are you putting the ground line of the 'scope probe? The ground reference is critical; if it's a significant length from pin 1 of the 555, you'll get wiggles in the waveform... You could also put a little bit of resistive load on the output to ground to see if that clears up the ring... (i.e. 100 ohms?)

Cheers