Archive for January 22nd, 2019

Astable Multivibrator: DSO150 vs. Capacitor Voltage

With the astable blinking green, I had to do this:

DSO150 - 2N7000 astable cap voltage
DSO150 – 2N7000 astable cap voltage

It blinks every two seconds because it uses 1 MΩ timing resistors, rather than the 2 MΩ resistors in the first version.

Because the DSO150 runs from the internal battery, you can clip it anywhere with few ill effects. The blinky runs from a battery, too, but connecting a high-impedance node to what’s basically the power line common may lead to heartache and confusion; it’s generally a Bad Habit.

A closer look at the DSO150 screen shows the expected bipolar exponential waveform across the 1 µF timing cap:

DSO150 - 2N7000 astable cap voltage - screen detail
DSO150 – 2N7000 astable cap voltage – screen detail

The scope triggering seems iffy, as the trace capture pauses every now and again for no apparent reason. This may have something to do with the very slow sweep speed; at 500 ms/div, the complete waveform takes forever to accumulate.

At least we know the signal lies well within the DSO150’s bandwidth!

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