Mindsensors NXTMMX-v2 User manual
What is NXTMMX-v2
NXTMMX is a multiplexer to
control additional NXT (or
EV3) Motors from your NXT
or EV3.
Connections and Placement
NXTMMX can be connected to any of the four sensor ports of NXT
or EV3 by using standard cables from NXT set or FlexiCable from
mindsensors.com.
Connect your motors to ports specified as M1 and M2.
Connect NXT or EV3 to port specified as ‘NXT’.
Additional Digital Sensors (or another NXTMMX) can be connected
to port specified as ‘Sensor’.
NOTE
Port specified as ‘Sensor’ on NXTMMX only supports I2C or Digital
sensors or multiplexers.
If you intend to daisy chain several NXTMMX’s or other digital
sensors please read the relevant section from the Advanced
Information Appendix of this doc.
Mounting NXTMMX on your contraption
The holes on the NXTMMX enclosure are designed for
tight fit of Technic pins (or axles) with ‘’ cross section.
The holes however are not designed for repeated
insertions/removals of these pins.
To mount NXTMMX on your contraption we suggest that you use two
dark gray ‘Technic Axle 3 with Stud’ as shown.
Insert axles from the top of the device and secure with a bushing on
the back or mount it on your contraption directly.
Alternately you may use blue ‘Technic Axle Pin with
Friction’ as shown.
While disassembling contraption leave the pins on the device.
Supplying power to your NXTMMX
The NXTMMX has Green terminals to connect external battery.
Copyright © 2016 mindsensors.com 1/14
NXTMMX-v2
User uide
NOTE
NXTMMX is rated for external power supply of 10 volts DC max.
Ensure to not exceed this value. While connecting external battery
ensure correct polarity.
Battery Options:
6AA batteries (rechargeable or non-
rechargeable).
To hold and mount these batteries you can
purchase a holder with NXT mounts from
the following location.
http://www.mindsensors.com/ev3-and-nxt/57-6aa-battery-holder-
with-ev3-mount
RC rechargeable battery
- 7.2Volts or 9.6Volts Ni-
CD or Ni-MH RC
rechargeable battery.
You can buy such battery
and it’s charger in local toy
store.
To connect these batteries to NXTMMX
you can purchase a connector cable from
the following location:
http://www.mindsensors.com/rpi/10-rc-battery-pack-connector-
cable
Lithiu -Poly er Battery (also known as
Li-Po or LiPo batteries)
With NXTMMX use 7.4 Volts battery.
Select the capacity based on your load
and anticipated duration of use. (For
nominal load we recommend 7.4Volts 800
mAh battery.)
You can purchase these batteries in electronic hobby stores or on-
line RC toys stores. An example url is here:
To connect these batteries to your NXTMMX you
can purchase connector pins from the following
location:
http://www.mindsensors.com/ev3-and-nxt/120-lipo-battery-adapter-
pins?search_query=lipo&results=1
Copyright © 2016 mindsensors.com 2/14
Feature Highlights
Table below lists the important features provided by the NXTMMX.
To use these features in your specific programming environment
please read your API help file (or NXT-G block help file) or program
header file.
Feature Description
Timed Control of each
motor
Each motor can be run for a specified
duration of time.
Encoder control of each
motor
Each motor can be run from its
current Encoder position to a new
position (with or without a specific
speed).
Speed control of each
motor
Speed of each motor can be controlled
in timed run or encoder based run.
Brake Vs Float while
stopping the motors
Each motor can be set to Brake (where
motor shaft can not be turned easily)
Vs Float (where motor shaft is free to
rotate by external force.
Holding Encoder position At the end of run hold the encoder
position (i.e. motor turned by external
force is restored to last set encoder
position).
Turning motor by degrees Move it in forward or reverse
direction.
Turning motor by
rotations
360 degrees makes one rotation.
Running operations
asynchronously
While a motor is running other
operations may be performed.
Running motors for
unlimited duration.
While motors are running you can also
perform other operations. NOTE:
When motors are set to run for
‘Unlimited Duration’ they will continue
to run until a Stop command is issued
(or power is disconnected). In other
words after starting the motors for
‘Unlimited Duration’ if your program
exits without stopping the motors
they will continue to run.
Stopping motors abruptly.
Reading Motor Encoders You can read the value of each
encoder from the NXTMMX.
Copyright © 2016 mindsensors.com 3/14
Programming Techniques for NXTMMX
EV3 Method:
To use capabilities of the sensor please download EV3
blocks available at the following URL:
http://www.mindsensors.com/index.php?
controller=attachment&id_attachment=156
Installation instructions for EV3 block are available at:
http://www.mindsensors.com/content/13-how-to-install-blocks-in-
ev3
Download EV3 sample program from following URL and modify it to
suit your needs.
http://www.mindsensors.com/index.php?
controller=attachment&id_attachment=155
NXT-G Method:
Please download custom NXT block from following
URL and import it into your NXT-G IDE.
http://www.mindsensors.com/index.php?
controller=attachment&id_attachment=96
If you need instructions on how to import this block in NXT-G visit
following url:
http://www.mindsensors.com/content/21-nxt-g-blocks-how-to-
install-blocks
Also download sample NXT-G programs from following URL and
modify them to suit your needs:
http://www.mindsensors.com/index.php?
controller=attachment&id_attachment=106
NOTE
Ensure to use latest LEGO firmware on NXT (1.29 or higher).
RobotC Method:
Download the library file from following URL and at the top of your
RobotC program file include it with following directive:
#include "NXTMMX-lib.h"
Copyright © 2016 mindsensors.com 4/14
Download library file and sample program from following URL:
http://sourceforge.net/projects/rdpartyrobotcdr/
Also ensure to download the help file
NXTMMX-README-RobotC-api.ht l, this file explains various
functions available for your program.
NXC Method:
Download the library file from following URL and at the top of your
NXC program file include it with following directive:
#include "NXTMMX-lib.nxc"
Library file URL:
http://www.mindsensors.com/index.php?
controller=attachment&id_attachment=68
Ensure to download the help file NXTMMX-README-nxc-api.ht l,
this file explains various functions available for your program.
You can also download sample program from this location and modify
it to meet your needs.
Current Characteristics
Average current consumption of this device is about 5.0 mA.
NXTMMX can deliver upto 1 Amp current per NXT Motor attached.
Drawing of excessively large current (such as incorrect motors or
stalled motors) will result in internal shutdown until the situation is
corrected.
I2C Bus address
Factory Default Address: 0x06
Changing the I2C Bus Address:
The I2C bus address of NXTMMX can be changed. To set an address
different from default address send sequence of following
commands on the command register:
0xA0 0xAA 0xA5 <new I2C address>
Note: Send these commands with no break/read operation in
between. This new address is effective immediately. Please note
down your address carefully for future reference.
Instructions for changing the I2C address can be found at:
NXT and EV3
Copyright © 2016 mindsensors.com 5/14
APPENDIX A - Advanced Information
I2C Registers:
The NXTMMX appears as a set of registers as follows:
Register Read Write
0x00-
0x07
Firmware version –
Vxxxx
-
0x08-
0x0f
Vendor Id –
mndsnsrs
-
0x10-
0x17
Device ID – NxTMMX -
0x41 You can read the NXTMMX
battery voltage at this
register.
(voltage in milli-volts =
register value * 37).
for EV3 compatible firmware
voltage is relocated to
register 0x90
Command
Motor 1 Write Para eters
0x42 Encoder Target for Motor 1
(long)
0x42: Least Significant Byte
0x43: Byte 2
0x44: Byte 3
0x45: Most Significant Byte
Encoder Target of Motor 1
(long)
0x46 Speed for Motor 1 (byte) Speed for Motor 1 (byte)
0x47 Time to run in seconds for
Motor 1 (byte)
Time to run in seconds for
Motor 1 (byte)
0x48 Command register B for
Motor 1
Command register B for
Motor 1 (set this value to 0 as
this is for future use)
0x49 Command register A for
Motor 1 (read the description
below for details of this
register).
Command register A for
Motor 1 (read the description
below for details of this
register).
Motor 2 Write Para eters
0x4A Encoder target for Motor 2
(long)
0x4A: Least Significant Byte
0x4B: Byte 2
0x4C: Byte 3
0x4D: Most Significant Byte
Encoder Value of Motor 2
(long)
Copyright © 2016 mindsensors.com 7/14
0x4E Speed for Motor 2 (byte) Speed for Motor 2 (byte)
0x4F Time to run in seconds for
Motor 2 (byte)
Time to run in seconds for
Motor 2 (byte)
0x50 Command register B for
Motor 2
Command register B for
Motor 2
0x51 Command register A for
Motor 2 (read the description
below for details of this
register).
Command register A for
Motor 2 (read the description
below for details of this
register).
Motor Read Para eters
0x62 Encoder position of Motor 1
(long)
0x62: Least Significant Byte
0x63: Byte 2
0x64: Byte 3
0x65: Most Significant byte
-
0x66 Encoder position of Motor 2
(long)
0x66: Least Significant Byte
0x67: Byte 2
0x68: Byte 3
0x69: Most Significant Byte
-
0x72 Status Motor 1 (byte). See
section below for details of
this register.
0x73 Status Motor 2 (byte). See
section below for details of
this register.
0x76 Tasks Running for Motor 1
(byte)
0x77 Tasks Running for Motor 2
(byte)
Registers for Advanced PID
control
Writing these registers has
i ediate effect on
operation. These registers
will be reset to factory
default values upon power
cycle.
0x7A Kp for Encoder Position
Control (int)
0x7A: Least Significant Byte
0x7B: Most Significant Byte
Kp for Encoder Position
Control (int)
0x7C Ki for Encoder Position
Control (int)
0x7C: Least Significant Byte
0x7D: Most Significant Byte
Ki for Encoder Position
Control (int)
Copyright © 2016 mindsensors.com 8/14
0x7E Kd for Encoder Position
Control (int)
0x7E: Least Significant Byte
0x7F: Most Significant Byte
Kd for Encoder Position
Control (int)
0x80 Kp for Speed Control (int)
0x80: Least Significant Byte
0x81: Most Significant Byte
Kp for Speed Control (int)
0x82 Ki for Speed Control (int)
0x82: Least Significant Byte
0x83: Most Significant Byte
Ki for Speed Control (int)
0x84 Kd for Speed Control (int)
0x84: Least Significant Byte
0x85: Most Significant Byte
Kd for Speed Control (int)
0x86 Pass Count – The PID
controller repeatedly reads
internal encoder ticks this is
the number of times the
encoder ticks reading should
be within tolerance. (default
5)
Pass Count – Higher Pass
count gives more time to
position internal encoder thus
providing better accuracy in
positioning but will take
longer time. Change this only
if you need different motor
positioning speeds and
accuracy. (For normal usage
default values will be OK).
0x87 Tolerance – The Tolerance (in
ticks) for encoder positioning.
(default 80).
Tolerance – the accuracy you
desire while positioning. Low
number will position the
encoders more accurately but
may take longer time. Change
this only if you need different
motor positioning speeds and
accuracy. (For normal usage
default values will be OK).
0x90 Voltage value
Supported I2C Commands:
CMD Hex Description
R 0x52 Reset all Encoder values and motor parameters. (This
does not reset the PID parameters).
S 0x53 Issue commands to both motors at the same time for
Synchronized starting of both motors.
Motor Stopping Co ands
a 0x61 Motor 1: Float while stopping.
b 0x62 Motor 2: Float while stopping.
c 0x63 Motor 1 and 2: Float while stopping.
A 0x41 Motor 1: Brake while stopping.
Copyright © 2016 mindsensors.com 9/14
CMD Hex Description
B 0x42 Motor 2: Brake while stopping.
C 0x43 Motor 1 & 2: Brake while stopping.
Encoder Reset Co ands
r 0x72 Motor 1: Reset Encoder to zero
s 0x73 Motor 2: Reset Encoder to zero
These commands are issued on command register (0x41).
Motor Command Register Explained
Each motor has two command registers (Register A and Register B).
In current release Register B is reserved for future use and must be
set to zero.
Bits in Register A should be set to 1 to avail functionality as
described below.
Register
Bit
Turn this bit to 1 for following functionality
Least
significant
bit (bit 0)
Speed control of your otor. The NXTMMX will
honor speed values specified in the speed register for
the respective motor.
Bit 1 Ra p the speed up or down. While starting the motor
or changing speed the NXTMMX will ramp up or ramp
down the power to new value.
If this bit is zero the power changes are sudden e.g.
full power is applied to motors as they start.
Bit 2 Relative change based on encoder values. This is
useful when Bit 3 is turned on and in this case the
NXTMMX will make a relative movement from last seen
Encoder position (it will add the new Encoder position
to old position and move to that resulting position).
Useful when turning by degrees or rotations.
If this bit is 0 the Encoder positions are taken as
absolute values.
Bit 3 Encoder control of your otor. The NXTMMX will
honor Encoder values specified in Encoder position
register for respective motor. If speed values are also
specified and speed bit is set on motors will rotate to
new encoder position with the specified speed.
Bit 4 Brake or Float at the co pletion of otor
ove ent. If this bit is 1 motor will Brake at the
completion otherwise it will float.
Bit 5 Encoder active feedback. This bit is used when
Encoder control is used. If this bit is set to 1 at the
completion of motor movement the NXTMMX will
continue to hold the Encoder position (i.e. if motor is
Copyright © 2016 mindsensors.com 10/14
Register
Bit
Turn this bit to 1 for following functionality
turned by external force NXTMMX will try to restore
it to last specified Encoder position). If this bit is
zero the motor may float.
Bit 6 Ti ed control of your otor. The NXTMMX will
honor the time specified value in ‘Time to run’ register
and run the motor for specified time. (If Time control
bit as well as Encoder Control bit is on the Timed
control has precedence over encoder control).
Most
significant
bit (bit 7)
GO. When this bit is set to 1 all above bit values are
brought into effect. This is useful to synchronized
starting of both motors. As it takes some time to write
each motor’s register values. The I2C command ’S’ can
be used to change these bits to 1 for both motors at
once.
Motor Status Register Explained
Each motor has one status register. Each bit in status register
indicates various situations with the motor as explained below.
Register
Bit
Value 1 indicates the situation is true
Least
significant
bit (bit 0)
Speed Control is ON. Motor is programmed to move
at a fixed speed.
Bit 1 Motor is Ra ping (up or down). If the Power ramp is
enabled this bit is 1 while the motor is ramping (while
changing its speed).
Bit 2 Motor is powered. (This may not mean motor is
moving.)
Bit 3 Positional Control is ON. The motor is either moving
towards desired encoder position or holding its
position.
Bit 4 Motor is in Brake ode. (0 value of this bit means
motor is floating).
Bit 5 Motor is overloaded. If the external load prevents
motor from achieving desired speed this bit is set to
1.
Bit 6 Motor is in ti ed ode. This bit is 1 while the motor
is programmed to move for given duration.
Most
significant
bit (bit 7)
Motor is stalled. The external load caused the motor
to stop moving.
Running Motors for Unli ited Duration
Copyright © 2016 mindsensors.com 11/14
Not specifying Encoder Control or Timed Control bit will result in
unlimited running of motor (the speed control is honored if
specified). To stop motors started with ‘Unlimited Duration’ use
respective Stop command from the command set.
NOTE
When motors are set to run for ‘Unlimited Duration’ they will
continue to run until a Stop command is issued (or power is
disconnected). In other words after starting the motors for
‘Unlimited Duration’ if your program exits without stopping the
motors they will continue to run.
How to detect if motor is moving or not moving:
In General:
Anytime when the ‘Stalled’ bit is 1 the motor is not moving.
Running in encoder ode:
During moving:
Position Control bit (bit 3) is 1
‘Motor is Powered’ bit (bit 2) is 1
Finished moving normally:
All bits are zero
Stopped due to stall:
Position Control bit (bit 3) is 1
‘Motor is Powered’ bit (bit 2) is 1
Stalled bit (bit 7) is 1
Running in ti ed ode:
During moving:
Timed Mode bit (bit 6) is 1
‘Motor is Powered’ bit (bit 2) is 1
Finished moving normally:
All bits are zero
Stopped due to stall (while time is not over):
Timed Mode bit (bit 6) is 1
‘Motor is Powered’ bit (bit 2) is 1
Stalled bit (bit 7) is 1
Stopped due to stall (after time is over):
All bits are zero.
Connecting other sensors on daisy chain port of NXTMMX:
You can connect only I2C digital sensors (or controllers) to the daisy
chain port of NXTMMX.
In other words you can not connect Touch sensors (which are
Analog) or most of the LEGO EV3 sensors (which are UART).
Copyright © 2016 mindsensors.com 12/14
Daisy chaining NXTMMX:
If you are daisy chaining upto 5 NXTMMX you should change I2C
address of all but one NXTMMX.
For example change the second NXTMMX to address to 0x08 third
to 0x10 and so on. (or something that does not conflict with any
other device address that you are attaching on the same port).
See the 'I2C Bus Address' section above for information on
changing the I2C address.
Install the program on your NXT attach the NXTMMX to Port 1
(attach only the NXTMMX for which you need to change the
address) and run the program follow on screen instructions to
select new address and update it.
(With a pencil make a note of the new address on the NXTMMX).
While using this NXTMMX in your program use the new address
(picture below shows where to use the new address in NXT-G
program):
If you are using any other programming environment the API
reference should indicate where to specify the new address.
If you are daisy chaining 5 or more NXTMMX or other digital
sensors you may have to disable Pull up resistors in some of the
devices. The Pull up resistors in NXTMMX can be disabled by
installing a special firmware.
For special firmware with pull ups disabled write an e-mail to
Follow the firmware upgrade procedure mentioned below.
Upon upgrade the NXTMMX must always be used with a device with
Pull up resistor in it. (e.g. Ultrasonic Sensor)
TIP
Upon upgrade write on the NXTMMX with a pencil that pull ups in it
are disabled.
Theory behind this:
Copyright © 2016 mindsensors.com 13/14
The I2C specification specifies that there be only one pull up
resistor on the I2C bus. The specs also recommend that the pull up
resistor be in the master device and slave devices should not have
pull up.
In case of NXT the pull ups are in sensors. When you daisy chain
multiple sensors on one I2C bus the pull ups start to add up and
that deteriorates the quality of communication between the NXT
and the sensors. On a smaller scale (usually up to 5 devices) this
deterioration has no effect on I2C network performance however
when you add more devices you may encounter data errors.
Upgrading NXTMMX firmware:
The NXTMMX is shipped with latest stable firmware if you need to
change/upgrade the firmware follow the procedure described at
URL below.
http://www.mindsensors.com/content/62-firmware-upgrader-for-
compatible-devices
If the Firmware Upgrader doesn’t detect your NXTMMX try this:
When the firmware Upgrader is looking for device attach the
device remove it momentarily and attach it again.
Copyright © 2016 mindsensors.com 14/14
Table of contents
