Assorted electronic circuits
Ultrasonic atomizer circuits
Homemade ultrasonic humidifier (ultrasonic atomizer)
Ultrasonic Atomizer Circuit
Multi-purpose ultrasonic atomizer circuit
Using an optical mouse CCD as a sensor reader
Optical mice often contain small CCD sensors:
A2051 chip, 16×16 sensor, datasheet
ADNS2610, 18×18 CCD, serial interface, datasheet
Mouse with an A2051 chip with a 16×16 sensor and PIC18 code
ADNS2610 read through a parallel port
Interfacing an optical mouse (USB) with a PIC sensorweb.c
PIC interface project
Idea–solar powered camera / wifi board:
Use an ESP8266 for WiFi / microcontroller (<$4).
Add a OV7670 camera module (<$5)
LiPo battery 100-600 mAh, 3.7v - 11v (<$2)
Solar panel ($1-$5), (http://www.aliexpress.com/item/2015-New-Mini-Portable-Solar-Power-3LED-Light-Keychain-Torch-Flash-Flashlight-Key-Ring-Gift-Rechargeable/32428752751.html?spm=2114.031010208.3.2.ZvUcW9&ws_ab_test=searchweb201556_9_71_72_73_74_75,searchweb201527_1,searchweb201560_9)
Or better, a supercapacitor, 2 in parallel for higher voltage (<$5), holds enough charge for a single round of wake up, snap picture, connect to wifi, send picture, sleep.
All together, < $15.
Universal battery eliminator circuit (UBEC), step down buck converters
MP2307
Adafruit page describing it.