Raspberry Pi camera module has pretty good characteristics and with software support you can do lots of interesting stuff. This is OK until you need more than one camera. What if you need more than one camera? There can be few solutions to problem – use another Pi per camera and join them with some webserver, use USB based webcams or try thing differently and multiplex multiple cameras to this single CSI connector. IVPort selected third option where he build camera interface multiplex module.
Multiplex module is designed as stack-able, so you can connect 4 cameras with single module and 3 GPIO control pins, 8 cameras with two modules that require 5 control pins and max of 16 cameras with 9 control pins. Of course cameras aren’t displaying all at once. Through software or manually you can select which camera to turn on while other are off. This solution is great for monitoring things around, building self aware robot platforms when cameras are stacked in cube. Other uses might be for building bullet time camera setup, because switching time between them is about 50ns.
Raspberry is a great small Linux machine which is ideal for connecting things to internet. Bunch of O/I pins allow connecting peripherals and sensors that can be accessed via web interface. Ferran Fabregas has been building a weather station with Raspberry Pi which sends data using Twitter application.
Currently his set up reads temperature and humidity data from DHT11 sensor and light intensity with LDR photocell. Raspberry Pi runs a python script which takes care of reading data from sensors. He also runs a local webserver where data can be loaded in nice graphical format which is updated in real time.
Very often analog gauges are used to measure some rate parameters. In most cases they are based on voltmeters where needle position is driven with PWM signal. Pat found a tachometer from old car lying around and decided to use it for displaying something useful – CPU usage. He starter building this project on Raspberry where tachometer would display its CPU usage.
First of all he had to figure out the signals needed to drive tachometer from 0 to full scale. He found a table with frequencies and PWM values on Tekronix 3252 information site. Then another issue was the signal level. Tachometer needs 5V to drive it while Raspberry Pi signal level is 3.3V, he used 7404 buffer to bring that level. The rest is Python code running on Raspberry Pi, which reads CPU value and then sends driving signal on pin 11.