I’ve ordered some photoresistors from Adafruit.com (and my 2×16 LCD screen). Materials arrive on 9/16/16.
Never used them before, but I’ll get familiar with them.
- Dark resistance is quite high (20K ohms or greater)
- Light resistance is somewhere in the (1K – 10K ohms range)
- Either analog input pins will be needed or a tuned comparator circuit will be used off board
- Look at expense, dev Arduino has resources, but was hoping to use a cost reduced version for the real thing
- UPDATE: I found a cost reduced Arduino at $1.60 each on eBay.
Simple evaluation circuit
I’m expecting the trip point to be somewhere around 30% of Vdd, but will update this article to reflect when I find out.
Let’s breadboard it!
I ended up using 2.4K resistors and ditching the pot in the circuit. I created a simple auto-calibration routine to set the trip point at the mid-point value on the ADC of the arduino.
I’ve built the LCD port expander as I need the “select” button to perform the calibration sequence for the photoresistors. Working on the calibration routines now.