1. BE Lesson 7: Make an automatic nightlight What is a Light Dependent Resistor (LDR) photocell? Use a photocell to make an automatic nightlight. Solder the nightlight circuit onto a protoboard. © 2012 C. Rightmyer, Licensed under The MIT OSI License, 20 July 2012

2. What is an Light Dependent Resistance (LDR) photocell? physical appearance electronic symbol more input light = less resistance = more current through it

3. Photocell allows hot water circulation only during the daytime (unless tank temperature is too hot) photocell

4. BE ckt 7-1. Automatic nightlight using Jameco #202403 photocell +  v LED 2N 3904 B C E Q1 photocell 330  100K  pot P1 Adapted from Electronic Kourseware Interactive, Discover Electronics, www.eki.com

5. BE ckt 7-1. Hookup diagram LED Photocell 2N 3904 (face down) 100K  pot + 9.0 volts 330  Jameco #202403 photocell

6. BE ckt 7-2. Automatic nightlight soldered on protoboard +  v LED 2N 3904 B C E Q1 202403 Photocell 330  16K  P1 Adapted from Electronic Kourseware Interactive, Discover Electronics, www.eki.com

7. Protoboard version of ckt 7-2

8. Front of protoboard (ckt 7-2) 16k = Orange-Orange-Orange 330 ohm = Orange-Orange-Brown PC = photocell 202403 16k16k + 330  LED + - 2N3904 PC

9. Front of protoboard (ckt 7-2) 16k = Orange-Orange-Orange 330 ohm = Orange-Orange-Brown PC = photocell 202403 16k16k + 330  LED + - 2N3904 PC