Two Questions on Voltage

First off was wondering is it possible to measure voltage by using a set up of leds and resistors in a bread board... i have a  couple of stepper motors and i want to figure out what i can get them to generate .. what id like to do is set it up where leds will light at different voltages generated eg when generator hits 2v first led lights and next dosent light till i hit 4v  and next dosent light till i hit 6v 

Have one small stepper motor which might output 6ish volts and i have another which i managed to get up to 10v plus out of it ... it  has 25volts written on it and i want to see can i get at least 16v from it .....

 so trying to turn these and measure with multimeter is a bit tricky ... would be handier if connected to bread board and leds light at different voltage ....

 

Also wondering actual voltage required to work things in house that are electrical .. eg where i live i get 240 volts supply ... have a keyboard that plugs into wall and runs from that supply  ... but will also run on batteries for a total of 9v   .... so wondering what in house actually requires 240 v ... cant see a kettle needing 240 v to run ??? so what if it was to run on batteries would it require ..  and as there is no adaptor to drop voltage on kettle like on keboard whats used internally to change the voltage ... same with the tv ... 

anyway your thoughts please ... Ty ty

 

 

Thank you will read this and

Thank you will read this and hopefully get a better understanding … and if anybody has a answer to the first part id be very happy

There is a nice presentation

There is a nice presentation about voltage, current, resistance and power: http://www.wisc-online.com/Objects/ViewObject.aspx?ID=DCE8204

For the first part of your question you can check for “Schmitt trigger” or you just use a microcontroller and read the voltage at an analog input,. But take care that the voltage is n ot higher than 5V. If it’s higher you need to reduce it with e. g. a resistor bridge.