| Electronics > Beginners |
| Interpreting results from my scope |
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| iamseth:
I have a 555 setup in monostable mode. I probed the output (pin 3) and the capacitor (pins 6 &7) to channels 1 and 2 respectively. The waveform looks like the one in the datasheet except I get some noise after the capacitor is charged up. I've attached the scope output image. My values for R1 and C1 are 1M and .1uF. Is this a concerning result and if so, what should I change to fix the issue? |
| StillTrying:
It looks like the triggering pulse on pin2 is longer than the monostable time, and it needs 100n across its supply pins. I think the GND is rising when the DIS pin starts to discharge the cap. |
| vk6zgo:
--- Quote from: iamseth on October 09, 2019, 11:19:15 pm ---I have a 555 setup in monostable mode. I probed the output (pin 3) and the capacitor (pins 6 &7) to channels 1 and 2 respectively. The waveform looks like the one in the datasheet except I get some noise after the capacitor is charged up. I've attached the scope output image. (Attachment Link) My values for R1 and C1 are 1M and .1uF. Is this a concerning result and if so, what should I change to fix the issue? --- End quote --- It is not unusual to get a bit of "overshoot" or "undershoot" with fairly sharp transitions in "real life". If you reduce the time/div & just look at the transitions, you will probably find they are sinusoidal. Because you are using a fairly long time/div setting, the 'scope makes a sort of "best guess"of the waveshape, hence the "squarish" look . On reflection, they are also low amplitude, so accurate representation of them will also be limited by the resolution of your ADC, so you will probably need to reduce the volts/div control as well. |
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