Multiple sensor outputs through 1 line??

Hey guys,

I am making an 8x8 array of IR sensors and want to scan over them in a keyboard arrangement. So basically I want to power up the rows one at a time and check the value of each sensor in the row (column values). Doing this quickly allows me to check over the whole array and require only a small amount of driving current.

I am controlling the power to the array using the arduino and a 4051 demux connected to 8 transistors feeding in 5V. The part I am a little confused about is how to connect the output of 8 sensors (one row) into one input of a 4051 mux.

I want to have simply 8 inputs and 8 outputs from the array. The inputs is easy but is it possible to tie the output of 8 sensors to one input? Bearing in mind that only 1 of the 8 sensors will be powered on.

I hope I have explained what I am trying to achieve.

Any help would be great. Cheers,

Jon.

do the IR sensors provide an 0..1 ON/OFF info or do they provide an analog voltage 0..5V ?

DO you have a link to the datasheet of the sensor?

The sensor arrangement is simply and IR emitter / photo-transistor pair and I am reading an analogue value from the transistor.
The emitter is a TSAL4400 and the transistor is TEFT4300. Easier to smack that into google and grab the info.

Cheers!
Jon.

The problem with this is that the sensors that are not powered will take their power from the powered sensor. Draw the wiring diagram and see. Yes the current will be going through two resistors but that is just a resistor of twice the value. You could isolate them by using a series diode before the input but that would require the sensor to develop at least 0.7V to overcome the forward bias drop of the diode. This would result in a great loss of sensitivity. Your best bet is to use analogue multiplexers to select the appropriate sensor.

Edit - forgot the 4051 link...

Not sure if you saw the playground page for the 4051, but it has a (blurry) schematic for..

The right image above is an example how to use two 4051 (one as demultiplexer and one as multiplexer) in a 8x8 Matrix to check 64 buttons or other digital Inputs just with one digital-In-Pin on the arduino

http://www.arduino.cc/playground/Learning/4051

I know you have the sensors already and I'm not sure of your application, but you might find it helpful to look at some of the projects based around using LEDs as sensors since a lot of the projects seem geared towards using matrices of detectors.

See the video on this page for a general example of the typical application of a matrix of light sensors: http://cs.nyu.edu/~jhan/ledtouch/index.html

Arduino Playground page for using an LED as a sensor: http://www.arduino.cc/playground/Learning/LEDSensor

Or if you really want to get crazy check out a commercial version from Sensacell: http://www.youtube.com/watch?v=xPgPYloUBdo&feature=player_profilepage

willnue