Multiple Sensors and Remote Sensors

Multiple Sensors - Multiplexing Any number of sensors can be grouped and read. This process is called "multiplexing" and I have experimented with both signal multiplexing and digital (ADC output) multiplexing and my preference is to multiplex at a digital level (ADC output) which reduces signal noise but requires a separate ADC for each sensor. I found that a low level analog signal required a small amount of time to settle at high read speeds before it is read which can cause a noise spike or misread signal value. Although the multiple ADC, digital multiplex circuit is more expensive, it is much less noisy at very low signal levels unless you use the Linear Technology (or other ADC manufacturers) ADCs with multiplexing built into the ADC chip. The multiplexed ADC chip is more complex to code and I prefer to use the simplest possible code in on this website. I have an example of a LTC2400 digital multiplex schematic below. This schematic can easily be adapted to most single channel ADC chips including the LTC2440. In this circuit, a standard multiplex "breakout board" is used and available at "Spark Fun". This board is available here: https://www.sparkfun.com/products/9056 Or go to the "Spark Fun" website and search for "Analog/Digital MUX Breakout" here: https://www.sparkfun.com The breakout board and chip is available for about $5.00 (US) Remote Sensors - WIRELESS The schematic/wiring diagram below is a remote sensor or wireless design. It uses a high quality XBee transceivers. I have wired and used this arrangement and it works well. It is important to understand that XBee wireless devices are powerful and reliable at long distances but you must buy the transmitter power that is right for you. When XBee says 300 feet in a spec, they mean 300 feet. A lot of the XBee components and Arduino code can be found at Adafruit - here: http://www.adafruit.com/ And the XBee preducts are here : http://www.adafruit.com/search?q=xbee Adafruit is one of the best DIY electronics sites on-line  -  their prices, products, and documentations are exceptional.