# Making a electrical signal detector (Inputs from multiple source)

I am working on an electrical project that, actually works something like a touchscreen digitizer, where I have to generate multiple inputs from over 50-100 sources, and I need to check from which sensor or a group of sensors (probably 3-5) are giving the signals, and then which sensor among the group has the highest electrical signal.

So I would like to know, if there is some way to do this. It has a lot of resemblance with the a resistive touch-screen digitizer, where there are many points that can send the signals, but the digitizer works by detecting exactly where the pressure has been exerted, and then it is sent to the micro-processor which calculates it according to the actual lcd screen.

A basic diagram, or a similar microprocessor reference will be appreciated.

My sensor are basically LDR's (or probably Photo Diodes), and I need to sense light intensity on a specific group of sensors. I am working on an academic project related to robotics.

The LDR's are placed at a distance of 10 mm from each other and arranged in the form of a matrix. So if I take a laser pointer and point to a specific LDR, I should get the reading (may be in number, count) of the active LDR sensor.

• What are the sensors and the signals? Are they voltage or current based? Are they resistive? Can you power them off while not measuring? How fast do you need to acquire the data? May 27, 2013 at 9:41
• The sensors are LDR's/photo diodes and the data must be acquired on regular intervals, it can be say 5-10 min, but at the same time I am not bound by time constraints, it can depend on a specific sensor being less resistive in case of LDR and voltage dependent in case of a photo diode, on any given time instant. May 27, 2013 at 9:48
• It might also be worth adding the rough distance between each group of sensors. Sometimes a multi-drop bus is a good way to do this sort of thing but options will depend on the distance. May 27, 2013 at 9:53
• Ok, that's a good idea (Thanks @PeterJ). Now I'll assume that the sensors are placed on a circular disc, in a matrix form, with all sensors placed at a distance of say 5-10 mm away from each other. But, now how do I process and find, the exact sensor sending in the signals. May 27, 2013 at 10:03
• I think you want a diode matrix combined with the multiplexer like this: leobodnar.com/products/BU0836/6x6.png , but the switches replaced with sensors. May 27, 2013 at 19:17

I'd use an analog multiplexer in combination with a 2D matrix. An example:

• Matrix of 64 sensors in an 8*8 configuration
• An eight-channel analog multiplexer with three-bit address input, each input channel connected to a row of the matrix
• A means of applying a voltage to each column in turn (for example, an 8-bit shift register and some transistors)
• A microcontroller with built-in ADC

1. Connect output pins of the uC to the address pins of the multiplexer and the input, shift, reset pins of the shift register.