Hello All
I am about to embark on what is allegedly the Hello World project of the breadboard beginner.
The Flashing LED project.
I have looked around the net and there are a couple of "recipe" based solutions eg: take these resistors, this transistor, this capacitor, this LED, this battery, put them all together like that hey presto the LED flashes.
Simply making an LED switch on and of is not all I want to achieve.
What I do want to achieve is an understanding of the physics at the fundamental level so that I can produce the outcome using any appropriate combination of components.
So far this is what I have gleaned from what knowledge I already have of the components involved.
First of all I know I don't necessarily need a transistor in this solution nor a capacitor. There are other ways of producing a pulsing voltage. eg: relays.
But for now I want to focus on an RC circuit solution. No transistor.
So that would be resistors, a capacitor, an LED an a power source.
Put simply I figure that what I need to do is attach a supply current to the capacitor anode and the LED to the capacitor cathode.
I then need to create a situation, using the resistors where the charge rate of the compacitor is less than it's discharge rate.
That way the capacitor will continue to charge from V=0 to the threshold voltage of the LED.
When the LED threshold voltage is reached the LED will then discharge the capacitor down to its threshold, the LED that is.
When the voltage in the capacitor falls to the threshold voltage of the LED the LED will turn off.
This is in effect your flash event.
The cycle is then repeated.
The duration of the flash event will be determined by the capacitor time constant as it discharges.
The frequency of the flash event will be determined by the difference between the charge rate and discharge rate of the capacitor.
All of these parameters will deteremine which components to use in the project. ie: capacitor and resistors.
In order to calculate these parameters for any given flash duration and frquency I am looking at the following formulae:
Charging : V = E(1 - e^(-t/RC)) where E = Charging source voltage volts; t = time seconds; R = resistor ohms; C = cap capacitance Farads; e = Eulers number
Discharging : V = V0 * ( e^(-t/RC)) where V = Capacitor charge volts; t = time seconds; R = resistor ohms; C = cap capacitance Farads; e = Eulers number
Time constant tau = RC where R = resistor ohms; C = cap capacitance Farads;
How does that sound? Am I missing anything?
Thanks
I am about to embark on what is allegedly the Hello World project of the breadboard beginner.
The Flashing LED project.
I have looked around the net and there are a couple of "recipe" based solutions eg: take these resistors, this transistor, this capacitor, this LED, this battery, put them all together like that hey presto the LED flashes.
Simply making an LED switch on and of is not all I want to achieve.
What I do want to achieve is an understanding of the physics at the fundamental level so that I can produce the outcome using any appropriate combination of components.
So far this is what I have gleaned from what knowledge I already have of the components involved.
First of all I know I don't necessarily need a transistor in this solution nor a capacitor. There are other ways of producing a pulsing voltage. eg: relays.
But for now I want to focus on an RC circuit solution. No transistor.
So that would be resistors, a capacitor, an LED an a power source.
Put simply I figure that what I need to do is attach a supply current to the capacitor anode and the LED to the capacitor cathode.
I then need to create a situation, using the resistors where the charge rate of the compacitor is less than it's discharge rate.
That way the capacitor will continue to charge from V=0 to the threshold voltage of the LED.
When the LED threshold voltage is reached the LED will then discharge the capacitor down to its threshold, the LED that is.
When the voltage in the capacitor falls to the threshold voltage of the LED the LED will turn off.
This is in effect your flash event.
The cycle is then repeated.
The duration of the flash event will be determined by the capacitor time constant as it discharges.
The frequency of the flash event will be determined by the difference between the charge rate and discharge rate of the capacitor.
All of these parameters will deteremine which components to use in the project. ie: capacitor and resistors.
In order to calculate these parameters for any given flash duration and frquency I am looking at the following formulae:
Charging : V = E(1 - e^(-t/RC)) where E = Charging source voltage volts; t = time seconds; R = resistor ohms; C = cap capacitance Farads; e = Eulers number
Discharging : V = V0 * ( e^(-t/RC)) where V = Capacitor charge volts; t = time seconds; R = resistor ohms; C = cap capacitance Farads; e = Eulers number
Time constant tau = RC where R = resistor ohms; C = cap capacitance Farads;
How does that sound? Am I missing anything?
Thanks