Using Grove devices to the EV3

After David Lechner announced ev3dev support for it I’ve been planning to offer myself a couple of BrickPi 3 from Dexter Industries (just one is not enough since the BrickPi 3 suports daisy chaining).

While I wait for european distributors to sell it (and my budget to stabilize) and since I’m also playing with magnets, I ordered a mindsensors.com Grove adapter so I can start testing Grove devices with my Ev3. Also got two Grove devices from Seeed Studio at my local robotics store, will start with the easiest one: Grove – Electromagnet.

ev3dev doesn’t have a Grove driver yet but since the adapter is an I2C device it recognizes it and configures it as an I2C host:

[  563.590748] lego-port port0: Added new device 'in1:nxt-i2c-host'
[  563.795525] i2c-legoev3 i2c-legoev3.3: registered on input port 1

Addressing the Grove adpter is easy, just need to follow the ev3dev documentation (Appendix C : I2C devices):

robot@ev3dev:~$ ls /dev/i2c-in*
/dev/i2c-in1

robot@ev3dev:~$ udevadm info -q path -n /dev/i2c-in1        
/devices/platform/legoev3-ports/lego-port/port0/i2c-legoev3.3/i2c-3/i2c-dev/i2c-3

So the Grove adapter is at I2C bus #3. According to mindsensors.com User Guide, it’s address is 0x42. That’t the unshifted address but fot i2c-tools we need to use the shifted address (0x21 – at the end of the ev3dev Appendix C doc there is a table with both addresses).

robot@ev3dev:~$ sudo i2cdump 3 0x21

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 56 31 2e 30 32 00 00 00 6d 6e 64 73 6e 73 72 73    V1.02...mndsnsrs
10: 47 61 64 70 74 6f 72 00 00 00 00 00 00 00 00 00    Gadptor.........
20: 4a 61 6e 20 30 34 20 32 30 31 35 00 31 32 46 31    Jan 04 2015.12F1
30: 38 34 30 00 00 00 00 00 00 00 00 00 00 00 00 00    840.............
40: 00 97 03 32 00 00 00 00 00 00 00 00 00 00 00 00    .??2............
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................

Acording to the User Guide, this is the expected content of the first 24 registers:

0x00-0x07: Software version – Vx.nn
0x08-0x0f: Vendor Id – mndsnsrs
0x10-0x17: Device ID – Gadptor

So I have a v1.02 Grove adapter.

To use the Grove – Electromagnet I just need to send a “T” (0x54) to the Command Register (0x41) to set the Grove Adapter into “Transmit” mode and next set the Operation Mode, which can be “Digital_0” (sending 0x02 to the Operation Mode register at 0x42) or “Digital_1” (sending 0x03 to the Operation Mode register).

So to turn the electromagnet ON:

sudo i2cset -y 3 0x21 0x41 0x54
sudo i2cset -y 3 0x21 0x42 0x03

And to turn it OFF:

sudo i2cset -y 3 0x21 0x41 0x54
sudo i2cset -y 3 0x21 0x42 0x02

Just a warning: with an operating current of 400 mA when ON the electromagnet gets hot very quickly – not enough to hurt but don’t forget to switch it OFF after use to prevent draing the EV3 batteries.

The same method (“T” + “Digital_0” / “Digital_1”) can be used with several other Grove devices, like the Grove – Water Atomization:

(a great way to add fog effects to our creations – just be careful with short circuits; if you add some kind of parfum you can also have scent effects)

Final note: you can use the mindsensors.com Grove Adapter with native EV3 firmware (just import the available EV3-G block) but if you are using ev3dev like me be sure to use a recent kernel (as of today, “4.4.61-20-ev3dev-ev3”) because older versions had a bug that caused some communication problems with I2C devices (the Grove Adapter is an I2C device).

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