I've been searching for some time on projects with LED strips and I'm having trouble with some calculations.
1. How can I calculate which resistor and which transistor (using the direct connection or Darlington connection) should I use for an unaddressable LED strip of given length?
In a simple RGB LED strip, that is not addressable, we have 4 lines (VIN, R, G, B). The lines R, G and B will be controlled via an ESP8266. The ESP8266 is a 3.3V device that can only provide 12mA on GPIO pins. To be able to provide enough current to fully light up a channel (~20mA for every 3 LEDs) I need to use transistors to raise the current to the point I need.
These are the calculations I already know:
- amps needed: (#LEDS / 3) * 20mA
- watts needed: V * I => 12V * (#LEDS / 3) * 20mA
What I still don't know how to calculate:
- With an NPN transistor's datasheet, find the base resistance I need to use that will make the emitter output enough current to fully light up a channel in the LED strip
- If a single transistor will not be able to achieve the desired current, how do I calculate the same as above but using a Darlington pair?
2. How many LEDs can 1 Arduino (specifically an ESP8266) control before we see some kind of lag?
An addressable LED strip has 3 lines (VIN, GND, DATA), VIN and GND can be wired in parallel but DATA needs to be wired in series if we have one single controller. I'm tasked with building a LED panel that would have more than 2000 LEDs (yes, that massive) and I'm a little afraid one data source will make the last LEDs take too long to receive the command and lag behind.
This is what I have researched so far:
My question on StackExchange that confused me more than helped: https://arduino.stackexchange.com/questions/52532/rgb-led-strip-is-too-dim
My topic on power supply that cleared how to calculate the power needed: http://forum.arduino.cc/index.php?topic=546221