Morning all
I am working on something a little unusual. I am using a number of LED's to show the amplitude of a signal.
Let's say 5 LEDs which each switch on when V>=x where x is different for each LED. Therefore as V rises each LED will switch on in turn and off as V falls.
Simple so far. However V is not only the variable to be measured but also the only voltage to the circuit. Therefore there is no stable power supply or voltage reference that could be used to compare V to.
The idea I am running with is to use an NPN in common collector configuration with a potential divider biasing Vbe so that each transitior switches on at a different level of V. A second NPN is used to current limit the stage so as V rises the current to the LED remains <~20mA.
I must admit this is my first foray into the practical applications of transistors. My spice simulations look promising but it is evident that, although the transistors turn on at different voltage levels the LED bank will look like it turns on as a group with LEDs individually getting brighter. I would like a more digital output. Any ideas for a second stage (current comparison maybe?)
The circuit below is repeated for each LED, with R46 controlling the voltage across Vbe.
Thanks for looking.
I am working on something a little unusual. I am using a number of LED's to show the amplitude of a signal.
Let's say 5 LEDs which each switch on when V>=x where x is different for each LED. Therefore as V rises each LED will switch on in turn and off as V falls.
Simple so far. However V is not only the variable to be measured but also the only voltage to the circuit. Therefore there is no stable power supply or voltage reference that could be used to compare V to.
The idea I am running with is to use an NPN in common collector configuration with a potential divider biasing Vbe so that each transitior switches on at a different level of V. A second NPN is used to current limit the stage so as V rises the current to the LED remains <~20mA.
I must admit this is my first foray into the practical applications of transistors. My spice simulations look promising but it is evident that, although the transistors turn on at different voltage levels the LED bank will look like it turns on as a group with LEDs individually getting brighter. I would like a more digital output. Any ideas for a second stage (current comparison maybe?)
The circuit below is repeated for each LED, with R46 controlling the voltage across Vbe.
Thanks for looking.