Matrix - Ball Rolling Switch

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1 Introduction

BAll Rolling Switch

• The Matrix-Ball_Rolling_Switch module is a ball switch. Its electrical characteristics are very similar to a mercury switch's however a mercury switch is easily broken, oxidized, leaking and not environment-friendly. This ball switch prevents all these issues.
• The switch is free to move any angle and if that angle is between 15 degrees and 45 degrees a signal will be generated and used as an input to a Schmitt trigger.

2 Features

• GPIO
• Small
• 2.54 mm spacing pin header
• PCB Dimension(mm):16 x 16

• Pin Description:

Pin	Description
S	Digital GPIO
V	Supply Voltage 5V
G	Ground

3 Basic Device Operation

Please connect Pin V to a power supply, Pin G grounded and Pin S to a digital output. When you move the switch pushing the internal metal ball to connect the trigger point a high level signal will be generated and output to a Schmitt trigger which reverses this signal to output a low level signal. When you move the switch pushing the internal metal ball away from the trigger point a low level signal will be generated and output to a Schmitt trigger which reverses this signal to output a high level signal.

4 Download Matrix Source Code

All the matrix modules' code samples are open source. They are maintained on GitHub: https://github.com/friendlyarm/matrix.git
Each branch in this hub contains the matrix modules' code samples for a board that the matrix modules can work with

• The matrix-nanopi branch contains the matrix modules' code samples for the NanoPi
• The matrix-nanopi2 branch contains the matrix modules' code samples for the NanoPi 2
• The matrix-tiny4412 branch contains the matrix modules' code samples for the Tiny4412;
• The matrix-raspberrypi branch contains the matrix modules' code samples for the RaspberryPi;

Please follow the steps below to get the source code:
Install the git utility on a PC running Ubuntu14.04

$ sudo apt-get install git

Clone the matrix code from GitHub

$ git clone https://github.com/friendlyarm/matrix.git

If this is successful a "matrix" directory will be generated, which will contain all the matrix modules' code samples.

5 Connect to NanoPi 2

5.1 Hardware Connection

Please refer to the following connection diagram to connect the Matrix-Ball_Rolling_Switch to the NanoPi 2:

Connection Details:

Matrix-Ball_Rolling_Switch	NanoPi2
S	Pin7
V	Pin4
G	Pin6

5.2 Compile Test Program

Please login the matrix hub and enter the nanopi2 branch

$ cd matrix
$ git checkout nanopi2

Compile the Matrix code

$ make CROSS_COMPILE=arm-linux- clean
$ make CROSS_COMPILE=arm-linux-
$ make CROSS_COMPILE=arm-linux- install

Note: please make sure to install the cross compiler "arm-linux-gcc-4.9.3" on your PC, which is used to compile files for the NanoPi 2.
Generated library files are under the "install/lib" directory. The test program is under the "install/usr/bin" directory. The modules are under the "modules" directory.

5.3 Run Test Program

Please insert a TF card which is flashed with Debian to a Linux host and mount its boot and rootfs sections.
We assume the rootfs is mounted to /media/rootfs then please run the following commands to copy the module, library and test program to the card.

$ cp modules /media/rootfs/ -r
$ cp install/lib/* /media/rootfs/lib/ -d
$ cp install/usr/bin/* /media/rootfs/usr/bin/

Insert this TF card to your NanoPi 2, power on and run the following commands to start the matrix-ball_switch program.

$ matrix-ball_switch

Here is what you should expect:

After you get the prompt "Lean the switch" please tilt the module to roll the ball making it touch the trigger point you will see "Switch[0]:1".

5.4 Code Sample

static struct sensor brSwitch[] = {
        {
                GPIO_PIN(7),
                IRQ_TYPE_EDGE_FALLING,
        }
};
 
int main(int argc, char ** argv)
{
    int i;
    int retSize = -1;
    char value[ARRAY_SIZE(brSwitch)];
    int devFD = -1;
 
    if (argc == 2) {
        brSwitch[0].pin = atoi(argv[1]);
    }
 
    printf("Using GPIO_PIN(%d)\n", brSwitch[0].pin);
    if ((devFD =sensorInit(brSwitch, ARRAY_SIZE(brSwitch))) == -1) {
        printf("Fail to init sensor\n");
        return -1;
    }
    printf("Lean the switch...\n");
    if ((retSize = sensorRead(devFD, value, ARRAY_SIZE(brSwitch))) == -1) {
        printf("Fail to read sensors\n");
    }
    if (retSize > 0) {
        i = 0;
        for (i=0; i<retSize; i++) {
            printf("Switch[%d]:%d\n", i, value[i]);
        }
    }
    sensorDeinit(devFD);
    return 0;
}