Array of hall sensors

Projects General Guidance
1

Hi folks,

I'm new to arduino. I read everything available about multiplexing and led-arrays and think I fully understand it.
What I want to do next is to build a hall-sensor matrix (8x8). Therefore I want to alter the led array in that way that I change the leds to normal diods and put a hall sensor behind each (with the needed resistor, like described here demonstration of Hall Effect Switch)

I want to add a multiplexer to the output (I need the other ports for other project based outputs). That output I want to put on the matrix row. For the input a multiplexer is added, too (columns of the matrix).

Now I want to multiplex through the outputs and set them in high and check all possible input for a sensor signal to clearify which hall sensor switch is activated.

Does that sound like a feasable plan or won't it work?

Thank for you help and guidance.

Best,

Simon

2

http://playground.arduino.cc/learning/4051

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

Ray

3

The resistor isn't needed in that tutorial, because you can use the internal pin pullup resistor instead.

4

The resistor isn't needed

Wasn't it Ohm that said, "A resistor saved is a resistor earned."?
XD

Ray

I rarely use the weak internal oull-up resistors because their value is not guaranteed. I'd rather put a physical component on the board for a nickel and know what I'm doing can be exactly modeled within the range precision of the component. At today's prices, I always buy 5% or 1% for metal film resistors.

But, yes, I suspect the internal pull-up would be appropriate in this case.

Ray

5

For this application, I think I would use a 74HC138 3-to-8 line demultiplexer, with each output driving a PNP transistor that switches the +5V supply to one column of Hall sensors (sadly, as each sensor need 4mA of supply current, you can't power 8 of them from a single demultiplexer output). I would connect the Hall sensor outputs together in rows (they are open-collector outputs) and use a 74HC4051 multiplexer chip to connect one row at a time to an Arduino input.

After selecting the column, you need to allow 25us (the power-up time of the sensor) before reading the input.