How to place 70 sensors - reed switches on arduino?

Question

Do it yourself

In the same place, only 14 can be on one piece, but you don’t want to overpay ...

Answer 1

arduino.ru/Tutorial/registr_74HC595 - may help

Answer 2

Lots of options. For example, shift registers 74LS165, we hang the required number in a chain, we send a latch signal from the arduino (1 output), then we issue clock pulses (another output) receiving the state of each of the inputs in sequence (1 input).
Or a matrix can be built, on the 74LS154 we display the number of one of the 16 lines (4 outputs), at the inputs we receive response lines (5 inputs will give 80 sensors).
I will add that the matrix has the advantage that it is necessary to pull much fewer wires to the sensors (16 + 5 = 21) in it than with multiplexing.

Answer 3

There is a special chip that interrogates a number of "dry contacts" and issues it in SPI. Can be cascaded. SN65HVS882 .

Answer 4

You need, judging by your question, a multiplexer. Although if you wrote more about your project, then it turned out to advise more specifically.
By the way, here is a similar project about "expanding" the number of inputs on arduino.ru is being discussed.
And here you can pick up different multiplexers Digital demultiplexers for GPIO expansion and decoding
Take a look at this project On the basis of 16×64 dot matrix LED design on dis...
In fact, in order to receive signals, you can use the matrix principle, like polling keyboard signals. Here Matrix keyboard , by the way, I also recommend looking here .
But if you take a look atATMEL Application Note AVR240 , creatively modify the circuit by adding multiplexer(s), get the result. But still, there are features with the receipt of multiplexed signals. Therefore, it is better to describe your task in more detail.