Trying to understand behavior of Inverter bit ....?

Hi all … I’ve officially become obsessed with these modules :smile:

I’m playing with the inverter bit, trying to see what I can come up with, and I’m having some issues understanding some things.

I have power>keyboard>inverter>oscillator>bargraph.

I would assume that with no key pressed, the barograph would light up, but that is not the case … Why?

What does it do if you take the oscillator out?

Hi @eroxx,
Your thinking is correct, but you may have a few things going on. Like @chris101 said, try removing the Oscillator to see what the Bargraph does then. My guess would be that the Bargraph would light up. If this is the case, put the Oscillator back before the Bargraph and try adjusting the frequency of the Oscillator. It may be turned down really low or really high, causing the Bargraph to light up in an unpredictable way.

For those curious about the operation of the Inverter module. It is essentially an inverter logic gate. The truth table in this Wikipedia article should outline the expected behavior.

Have you tried putting the Inverter after the Oscillator? I think that when no keys are pressed the Oscillator outputs a LOW signal (zero), so the Inverter should flip that value around to a HIGH signal (in theory) and light up all the LEDs of the Bargraph.

Although, you should keep in mind that the Bargraph takes input from the bit immediately before - in this case the Oscillator. If you want the Bargraph to show the values produced by the Keyboard, then you should plug the circuit like this:

Power > Keyboard > Bargraph > Oscillator
or Power > Keyboard > Inverter > Bargraph > Oscillator


Just as an extra, the Inverter usually takes digital input but it can also be used as a cheap bitcrusher/distorter on sound data or analog signals. Check this thread for more info Favorite extra modules to use with the Synth Kit

So i played around and still confused … (not surprising)

with power>keyboard>oscillator>inverter>bargraph,

I would expect bargraph to light up when NOTHING is pressed (this is the case) on the keyboard,.

But, I would expect bargraph not to light up when a key is pressed. Instead, it pulses. This behavior does not make sense to me …?

Because the oscillator is ‘pulsing’ the voltage - it’s going high and low, over and over. So the inverter changes that to off and on.

  /|  /|  /|  /         _    __    __    __   LED on
 / | / | / | /   --->    |  |  |  |  |  |  |
/  |/  |/  |/            |__|  |__|  |__|  |_ LED off

The inverter switches when the voltages passes the halfway point, 2.5 volts.

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Ok, but when a key is pressed, doesn’t that send voltage to the oscillator and result in an “on” signal? I’d think the inverter would stop that.

When I add a speaker after the inverter, the sound does not seem to pulse, it seems constant …

The keyboard sends a voltage to the oscillator that sets the frequency of the oscillation. Different keys send different voltages. The speaker emits a sound, which is an oscillation.