Wiring it up!

Now we'll wire up the sensor to the Feather ESP8266. I used a half-size breadboard for this, but if you're feeling bold you can solder the components together directly, or use an Adafruit perma-proto board.


Note that the sensor shown in this diagram (ALS-PT19)  is different from the one specified in this tutorial; we don't have the log-scale light sensor in Fritzing yet. The wiring is identical, though, so it shouldn't matter. In fact, you can use this sensor instead of the log light sensor and it'll work fine.

First, we need to build the voltage divider out of 1M Ohm (R1) and 470K Ohm (R2) resistors. 3.3v is connected from the ESP8266 to Vcc on the light sensor. The ground pin is connected to, of course, ground. The "out" pin is wired to the voltage divider (more on the voltage divider below).

Of course, if you know the formula for the calculation, you can just use that directly. I'm not a EE, though, so I'd have had to look it up anyway. Incidentally, the voltage divider is the first "project" in Hayes and Horowitz's classic "Learning the Art of Electronics" (Adafruit Product ID 3066) - it starts on page 11.

Test the voltage divider by applying 3.3v to Vin and measuring the voltage between the two resistors with your meter. It should read about one volt. Once that's working correctly, connect 3.3v to Vcc on the sensor and connect the other side to Vin of the voltage divider. Connect one side of R2 to R1 and the other to ground. Finally, connect Vout (the connection between the two resistors) to the single Analog pin on the ESP8266. The voltage divider assures that we will not exceed the ESP8266's input voltage restriction on the analog pin, which is one volt. Remember to connect the GND pin to ground.

Now we're ready to program the ESP8266!


This guide was first published on Aug 20, 2016. It was last updated on Aug 20, 2016. This page (Wiring it up!) was last updated on Jun 16, 2019.