Pololu Blog (Page 55)
Welcome to the Pololu Blog, where we provide updates about what we and our customers are doing and thinking about. This blog used to be Pololu president Jan Malášek’s Engage Your Brain blog; you can view just those posts here.
We are excited to welcome several new distributors that have joined Pololu over the past few months!
To start with, we have gained two new distributors in the United States. We have been following Adafruit Industries (New York, NY) for a long time – I remember receiving a SpokePOV kit as a birthday present back in 2007 – so we are particularly excited that they will now be selling some of our products. They are starting with the Zumo, which they featured in a recent new product video. We will also be distributing some of their products, such as the Adafruit Data Logging Shield for Arduino. Is there anything from Adafruit that you would like to see at Pololu? Please let us know in the comment section.
Anibit Technology (Cary, NC) is another new US distributor, founded in 2013 by engineer Jon Wolfe, who is marketing his own designs along with parts from Pololu and Adafruit. We are looking forward to seeing what else he will create!
Next, MiniRobot (Azcapotzalco, Mexico City, Mexico), joins a number of other Mexican distributors. They carry a large selection of parts, including many Pololu items, as well as Arduinos, components, and prototyping supplies.
Continuing south, we have a new distributor in Viña del Mar, Chile: Zambeca. In addition to carrying a number of Arduino, Lilypad, and robotics-related products, they have been posting some interesting-looking project videos on their blog (in Spanish). We have one other distributor in Chile, MCI Ltd – Olimex Chile, who has been with us since 2009.
We now have a distributor in China, ALSRobotBase, located in Harbin, Heilongjiang province. They have a whole “Pololu” category and are also offering to help customers in China with special orders.
For distributors in your area, you can check out our complete list of almost 200 distributors.
Get a FREE copy of Elektor magazine’s March issue with your order while supplies last. To get your free issue, enter the coupon code ELEKTOR0314 into your shopping cart. The magazine will add 6 ounces to the package weight when calculating your shipping options.
For other issues and more information, see our Free Elektor Magazine Offers page. All issues are now available for shipping worldwide!
Forum user solderspot recently posted on our forum about some modifications he’s been making to his Zumo robot. First, he added our optical encoders for micro metal gearmotors to his robot, which required using motors with extended back shafts and cutting holes in the chassis to route the wires from the encoders.
This allows his Zumo to navigate by dead reckoning, using just the information from the encoders.
He also mounted a sonar sensor on a servo to his robot, which enables it to find its way around a room by following the walls.
A series of articles on solderspot’s blog, starting with this one, covers his experience building and programming his robot. It looks like solderspot has further plans for the Zumo, including more sophisticated autonomous navigation, so watch his blog if you want to keep up with the latest developments.
We have new gyros fresh out of the oven. No, I’m not talking about a Greek dish. I’m talking about our new L3GD20H 3-axis gyro carrier.
One of the most important measures of a rate gyroscope’s performance is the amount of noise in its output, which is indicated by its noise density specification. Too much noise means that the gyro will be prone to spurious indications of rotation, and if the gyro readings are integrated to track orientation, noise will cause the calculation to drift over time.
Although sensor fusion can help compensate for this drift by combining the gyro data with an absolute reference (like magnetometer data), using a lower-noise gyro is likely to be a more effective way to improve orientation tracking accuracy. In that respect, one of the biggest improvements of the L3GD20H over its predecessor is that it has a 60% lower rate noise density (0.011 dps/√Hz compared to 0.03 dps/√Hz on the L3GD20).
In addition to accuracy and stability improvements, the L3GD20H offers other advantages. Its power consumption is lower and its start-up time is much shorter. A wider range of user-selectable output data rates is available, including lower frequencies that are appropriate for human gesture detection, and a data enable (DEN) pin allows readings to be synchronized with external triggers. The L3GD20H makes all of these features available in a smaller package than previous gyros, which has allowed us to design a correspondingly smaller carrier board for it while still keeping it breadboard-friendly. For more information, see the L3GD20H carrier product page.
If you don’t need the latest and greatest, the L3GD20 is still a nice sensor, and it’s a good time to grab one now that we’ve lowered the price of our L3GD20 carrier to only $14.95 until stock runs out.
Local indie artist and Pololu employee Tracey, intent on reviving her programming skills and exploring her budding interest in electronics, shed some light on her creative personality by making an LED banner for her band, Hope’s Edge. The banner is a briefcase-sized container that uses an addressable LED strip to shine through a stencil of the band’s logo in a wave of brilliantly changing colors. The stencil and the rest of the panels in the container are made from 1/16" black ABS, all of which were cut with our custom laser cutting service, and a sheet of gift-wrap tissue paper is taped to the inside of the front panel to act as a diffuser. The banner runs off of a 5V wall wart, which is boosted to 9V to power an Arduino Uno that runs Ben’s Christmas light LED code.
We are now carrying the latest version of SparkFun’s Inventor’s Kit (V3.1), which adds a mini screwdriver and replaces the translucent red breadboard from version 3 with an opaque white one that is easier to read. Version 3.1 includes everything else that was part of the previous version, such as the Arduino-compatible RedBoard and all of the additional components needed to build the 15 basic electronic circuits detailed in the guide.
For more information see the SparkFun Inventor’s Kit – V3.1 (with Arduino-Compatible RedBoard) product page.
When we designed the first version of the Pololu USB-to-serial adapter way back in 2004, using a USB Mini-B receptacle was an obvious choice: it was much smaller than the standard B-type connector, allowing us to keep the board compact, and it was readily available in surface-mount configurations that facilitate automated printed circuit board assembly.
We went on to use the Mini-B connector in lots of products, like our Maestro servo controllers and Wixel. Although the even smaller Micro-B connector became part of the USB specification in 2007, it didn’t seem to offer enough of an advantage over the Mini-B connector for us to immediately switch over. Continued…
Do you want to build your own weather monitoring station? This weather shield from SparkFun might be what you are looking for. In the form of an Arduino shield, this easy-to-use weather board can measure relative humidity, temperature, barometric pressure, and luminosity.
For more information, see the SparkFun Weather Shield for Arduino product page.
Forum user Hardsuit posted in this thread about the hub adapters he 3D printed for his robot, which is a roughly 1/4 scale RC Tachikoma from the Ghost in the Shell: Stand Alone Complex anime series. The adapters allow some of our universal mounting hubs to be used with VEX 4″ Mecanum wheels. You can find and download his STL file on Thingiverse.
The previous version of forum user Hardsuit’s Tachikoma.
The Tachikoma, which he has named Sapporo, also uses our Simple Motor Controller 18v15 and 29:1 Metal Gearmotor 37Dx52L mm. Some of the engineers here are GITS fans, and we are definitely looking forward to seeing it completed!
Here at Pololu we love USB and put a USB port on most of the microcontroller boards that we make. One of the lovable things about USB is that it provides a convenient power supply, but making good use of USB power presents a board design challenge: many of our products can be powered from either USB or an external source (e.g. batteries) and require a circuit to select between the two power sources. We call this circuit a power multiplexer, or just power mux.
A simple power mux like the one we use on the Wixel consists of a pair of diodes with a MOSFET that automatically disconnects the less-preferred power source. You can see another instance of the diode mux in the Orangutan SVP schematics (99k pdf). This works, but the forward voltage drop of the diodes can cause the output of the mux to be too low to power 5 V devices.
In the maker community, 5 V is very popular since it is the voltage standard used by numerous devices from Arduinos to Sharp Distance Sensors. Unfortunately for us, 5 V is not important for modern consumer devices like mobile phones, which operate at much lower voltages, so there is not much reason for semiconductor manufacturers to build the kind of devices that we need for good 5 V power multiplexers.
The USB power mux on many Arduinos uses a MOSFET, and does not suffer from the forward voltage drop problem, but it allows current to flow into the USB port in some situations, a potentially dangerous violation of the USB specifications.
So we were excited to find the FPF1320, a chip from Fairchild that implements a better MOSFET-based power mux circuit. The FPF1320 switches up to 1.5 A of current at 1.5 V to 5.5 V with an insignificant voltage drop, and it blocks reverse current into either of the sources. This chip seems like a great solution for USB power and other power-switching situations. Its tiny size, however, makes it inaccessible to most hobbyists:
Three FPF1320 BGA parts (two with solder balls facing up) among grains of rice and components in 0603, 1206, and SOT-23 packages.
That’s where we come in! We have made the FPF1320 available on a carrier board that breaks out all of its lines onto breadboard compatible pins and implements a minimal circuit to support automatic power switching. Our carrier board also breaks out a USB Micro-B connector to support USB power-switching applications. This diagram shows how the carrier would be used in a typical USB application:
Typical connection diagram for using the FPF1320 power multiplexer carrier with USB as the preferred supply.
Power multiplexers are useful for more than just USB. For example, many devices can be powered by both batteries and an external power jack, with external power preferred when it is available. Our FPF1320 carrier can be connected to two non-USB power supplies:
Typical connection diagram for using the FPF1320 power multiplexer carrier without USB.
Building a good power mux is a challenge, and the FPF1320 is not a perfect solution. One frustrating thing about it is that it is disabled (powered off) by default, and enabling it required us to build an additional power mux into the circuit! As you can see in the schematic below, we used the double-diode technique to drive the EN line high:
The diodes, unfortunately, take up more board space than the FPF1320 itself.
While typical applications involve USB and 5 V, our carrier is designed to work over the full range of input voltages supported by the FPF1320; therefore, extra consideration might be required to ensure glitch-free transitions between power sources. Specifically, we designed it to “prefer” one of the power supplies whenever it is present. The board will allow the preferred supply (and hence the output) to drop to 1.5 V or lower before switching, even if a better alternate source is available. Unfortunately, this guarantees that the voltage will always drop to below 1.5 V when switching from the preferred to the alternate source. The chip is capable of a seamless transition, and a more sophisticated application might involve monitoring the levels of both input voltages and switching in an intelligent way. You can also adjust the behavior to match typical applications using a few additional resistors or other components. Our carrier brings out the SEL line to make these kinds of modifications possible in your application.
For more information, see the FPF1320 Power Multiplexer Carrier product page.