I saw this schematic and I had problems finding out how it works:

As the voltage increases from zero, the first LED grows in brightness. Just when that LED is fully lit, the next LED begins to glow slightly. Each LED represents about 1 volt of change, when the circuit is operating from 9 volts.

according to the 4069 datasheet, the gates are not Schmidt triggers nor buffered, and the diagram for a gate seems quite simple:

If I'm right, the resistors form a voltage divider and just drive the LEDs. now I have these questions:

1. how the schematic works? why the next LED doesn't light up until the previous one is fully lit?
2. what does the first gate (left most gate, with two 1Mohm resistors) do  ?
3. what kind of modifications do I have to do, to make it work with 5V supply (the supply would be a constant 5V and the input would be a variable 5v)?

regards.

I saw this schematic and I had problems finding out how it works:

As the voltage increases from zero, the first LED grows in brightness. Just when that LED is fully lit, the next LED begins to glow slightly. Each LED represents about 1 volt of change, when the circuit is operating from 9 volts.

According to the 4069 datasheet, the gates are not Schmidt triggers nor buffered, and the diagram for a gate seems quite simple:

If I'm right, the resistors form a voltage divider and just drive the LEDs. 

I have these questions:

1. How does the circuit work? Why doesn't the next LED light up until the previous one is fully lit?
2. What does the first gate (left most gate, with two 1Mohm resistors) do?
3. What kind of modifications do I have to do, to make it work with a 5V supply? The supply would be a constant 5V and the input would be a variable 5V.

regards.