I thought the idea and approach looked interesting and decided to do a mini-project to test it out.
Diodes isolate the 4017 counter outputs in the event that two or more switches are closed at the same time, allowing simultaneous presses to be detected properly. The number of switches connected can be increased by cascading multiple CD4017 or by using a matrix style arrangement. The nice thing is that at all times the interface to the Arduino remains just 3 pins (Clock, Reset and the digital output from the matrix). Two counters in a matrix arrangement can be used to monitor up to 100 switches, still just using 3 interface pins.
According to the articles, Reset can be omitted but I decided to leave it in because reliable operation following the initial power-up reset depends on the CD4017 counter’s remaining synchronized with the Arduino counter. This is easiest done by resetting the 4017 at the start of every scan.
I have also implemented a scalable library to read the key matrix using the 4017 IC. The library
Allows definition of the size of the keyswitch matrix
Manages the scanning of the 4017 to read the matrix
Detects the transition from OFF state to ON state for each key
Implements software debounce and software auto repeat
Allows detection of multiple simultaneous key presses.
As a proof of concept, and to test the software, I implemented a 3x3 matrix. Attached are JPG images for the circuit, board layout and final product. It works really well and I can see that this keyboard matrix arrangement has the potential to save a lot of I/O pins. Scaling my circuit up to more switches should be straightforward.
The library and all associated documentation, including Eagle CAD files, can be found at my code repository in the signature block below.
I agree some of the suggestions were a bit 'dodgy', but the basic idea has merit. And yes, the switches can/should be soldered to the other side to make a usable keyboard :).
I used the 4017 matrix to control 37 keys of a small piano. I used your code but i dont know if i have to connect the reset output from arduino and where to connect.
For this reason I get different values for the pressed key if i switch off and then on the whole circuit.
Can you give any advice. I use 2 4017 connected as on the edn article.
Your are right.
To your example using one 4017 it is obvious how you done it.
But if you see the matrix example of the first edn article 4x3_matrix_2_4017
both reset are connected to outputs of 4017. If library can handle this i ll give a try connect both reset to arduino output.
The point of reset is to return the scanning to the zero position, so all 4017 resets need to be connected to the same Arduino output pin, as you seem to be now doing.
I had connect both MR (master reset) pins of 4017's to pin 10 of Arduino (i did changes today, to late for yesterday).
Now seems that every time finds the right key pressed but i dont know how to connect clock pins.
Acording to article with 2 4017's first ic clock comes form MCU and the last output goes to clock pin of second 4017.
Maybe I have to arrange different the connections. If I let it as is I got 2 issues.
Fisrt is that keys starts from number 4 and i dont have all numbers, last key doesnt work.
The clock signal should go into the clock of the first chip. The output on pin 12 of the 4017 is the clock for the next chip. Do you have a datasheet for the IC or are you just relying on the article? You should always get a datasheet for the chip you are using and get used to reading how to use the chips from the sheets (not always easy!).
