LDR Speed

Light dependent resistors are cheap and relatively wide-band light sensors, but they are a bit slow relative to photodiodes and phototransistors.

I used an AVR-based board to measure this, as follows:

* Put an LDR and 6.8k resistor in series between 5V and ground as a voltage divider.

* Attach the AVR's ADC pin to the connection between the resistor and LDR.
* Set another pin up to toggle an LED every 50msec.
* AVR samples ADConce each millisecond and spits out the value as a string on the RS232 port.

* PC logs serial port into file
*Use gnuplot to plot results.

As you can see, after approx 15msec the ADC value has settled quite well.


I don't quite know why the formatting got hosed.... but so be it.