Port Expander by Mindsensors.com
Tuesday, June 5th, 2007
Mindsensors.com now sells a port expander. It allows either running 3 motors together (no separate control over each motor speed or encoder readout) and multiplexing several digital (I2C) sensors on single input ports. You can order it via mindsensors.com NXT Accessories page.
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A Solenoid-Triggered Gun
Monday, June 4th, 2007
The NXT servos and other Lego motors are useful actuators, but it’s interesting to explore other actuators. The “Extreme NXT” book by Michael Gasperi, Philo, and Isabelle Hurbain shows how to use many more actuators with the NXT: LED’s, lamps, relays, motors, and a really exotic one called a muscle wire. But it’s always an interesting challenge to find out how to control new kinds of actuators, and it’s often even more interesting to find out ways to integrate them into the Lego/Technic/NXT building system.
In this project I tried to use a solenoid, which is basically an electromagnet that pulls a metal plunger when current flows through it. There were three main challenges in this project: to integrate the solenoid into a Technic mechanism, to find a good use for it in spite of the very short stroke (length of movement), and to drive it either from a motor port or from a sensor port. The difficulty in using a sensor port is that sensor ports cannot provide the high current required to activate the solenoid.
A web page describes the project with pictures and a short video. If you are interested, you may also want to join the lively discussion on actuators in the hardware forum.
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Toy Piano Interfaced to NXT
Sunday, June 3rd, 2007
Gasperi does it again! Here’s a toy piano with 23 ’switches’ (i.e. keys) interfaced to one NXT port, using two PCF8574s. More info here.
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Mindsensors.com Port Expander
Friday, May 11th, 2007
Here’s an image of the prototype port expander of mindsensors.com. As you can see, it will allow connecting 3 digital sensors to one port. I’m not sure, but it probably can connect multiple expanders to connect even more sensors. I’ll post more details on availability and use when I get them.
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News of the Month!
Thursday, May 10th, 2007For those who are not very familiar with the nitty-gritty of the NXT digital I2C bus, I wish to highlight the significance of the ‘Homebrew NXT port expander’ published on NXTasy.
As many have experienced the major limitation in the NXT is the number of sensor and motor ports. The only solution so far was using another NXT, communicating with Bluetooth with the first NXT (or RCX communicating with other means, like published a while ago). HiTechnic has been developing an active sensor multiplexer for some time (a picture of the prototype is here). This multiplexer will allow connecting 4 sensors – either passive (e.g. touch sensor), active (e.g. light sensor) or digital (e.g. sonar), to a single NXT port.
The solution presented by xw25adc is different – his port expander connects in series just the four ‘digital’ wires from the 6-wire NXT port – the +4.3V, the ground and the two digital I2C wires. Well, I’m getting too technical… Let’s stop that.
So what this so innovative about xw25adc work? To connect more then one digital sensor to a one port (i.e. a common ‘I2C bus’) you must have the sensor recognize that other sensors are connected. Why? Because the total of all sensors’ pull-up resistors must equal 82kOhm. If you naively connect two digital sensors, the pull-up resistance equals to two 82kOhm resistors in parallel which gives 82kOhm/2=41kOhm and the sensors will not function.
Anyone who read mindsensors.com manuals might notice a feature called ADPA: Supports Auto Detecting Parallel Architecture (ADPA) for sensors. This means that ACCL-Nx can coexist with LEGO or third party digital sensor on the same NXT port. This enables user to employ several sensors on the same port without the need of external sensor multiplexer, reducing the overall size.” This feature is just what one need to solve the previous problem – activating the ADPA on mindsensors.com sensors (it is shipped turned off) make them sense and recognize if more sensors are wired to the same port, and change the pull-up resistance to compensate this. xw25adc MUST have activated the ADPA feature, and used the compass sensor “advanced” I2C commands to change his ‘address’ from the default value 2 to 4. As far as I know, this is the first demonstration of this feature in action. Now some may ask - Wow! Can I do it too? Well, I can tell you that mindsensors.com have a prototype of a similar port expander in hand. In a few days I will post an image of this prototype when it reaches me. I’m currently working on a simple PC/Mac application that will ‘manage’ sensors – change ADPA on and off, change address etc. If I get some help from Lego/NI this application might even incorporate into the ‘Tools’ menu in NXT-G (no promises…).
One final technical detail – what differs between HiTechnic sensor multiplexer and mindsensors.com multiplexer? The former also allow connection of passive and active sensors, while the later supports only digital sensors (actually, only digital sensors which do not require 9V supply). This requires active components to regulate which sensor’s analog readout is transfer to the NXT at any moment. For these reasons, the HiTechnic multiplexer is expected to be more expansive (and it require 9V supply) then the passive mindsensors.com ‘I2C expander’.
Guy Ziv
NXTasy.org
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Perfect Pitch: Accurately Recognizing Tones
Sunday, April 29th, 2007
This home-made device allows the NXT to accurately recognize tones, as well as to produce a fairly strong tone at a particular frequency. Click on the image for details.
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Keep the volume down, or this robot will turn off the TV
Saturday, March 17th, 2007
This home-made i2c-controlled infrared remote control can turn off the TV (or give it other commands, like lowering the volume or change channels). It is used in this robot to turn the TV off if the sound is too loud.
The most interesting aspect of this project is the use of a microcontroller in the circuit. The microcontroller listens to i2c transmissions that the NXT sends via one of the sensor ports. The transmission from the NXT contains the infrared command to send. Once such a transmission is received, the microcontroller generates the appropriate infrared signal.
The full description of the project describes how to program a low-cost microcontroller ($20 will buy both the microcontroller and the device to program it) and how to interface it to the NXT. The full description also includes a short video showing the robot actually turning of a TV with this home-made remote.
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Sensor Building Kit for NXT with PCF8574 IC
Wednesday, March 14th, 2007
Here’s a new product from mindsensors.com. This kit is an ideal platform for you to design and build your own sensor. The kit comes with all the necessary parts to do Input/Outputs with NXT brick.
The kit contains:
- PCB
- PCF8574 IC
- appropriate capacitors
- appropriate resistors
- NXT type socket
- 10 pin header
Note: requires soldering.
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NXT Compatible Sockets and Plugs
Wednesday, February 7th, 2007
For a long time, the NXT style RJ12 plugs and sockets were unavailable in market. They are now sold by mindsensors.com. The order page is here (it is not accessible from their main webpage for some reason).
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New Gyro Sensor announced by HiTechnic
Wednesday, February 7th, 2007
A new product announcement by HiTechnic:
“The HiTechnic Gyro is a single axis gyroscopic sensor that measures the rate of turn in the plane of the sensor. Using the HiTechnic Gyro Sensor Block for Mindstorms NXT-G, the program will get a signed value that represents the rotation rate in approximate units of one degree per second. The maximum rotation rate which can be measured is +/- 360 degrees per second.
The sensor is housed in a standard LEGO sensor housing.”
Together with the other products announced earlier this week (IR sensor, IR link and motor and sensor multiplexers), it seems there will be a lot more options for NXT in the near future!
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NXT-G blocks for Mindsensors.com products
Monday, February 5th, 2007Mindsensors.com has started a repository for NXT-G blocks. These blocks allow NXT users having mindsensors.com PSPNx PS2 controller interface sensor, or the mindsensors motor multiplexer, to use these devices in NXT-G. The blocks are available for download here.
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Bigger Font for NXT LCD Display
Saturday, January 6th, 2007The standard font for the NXT is 6W x 8H pixels per character. The RobotC development system now supports a larger font where characters are 12W x 16H. Here’a a photo of the NXT LCD comparing the standard and expanded font sizes.
The font file was developed by Jason Rail…. Thanks.
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