Pololu Blog (Page 62)
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 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.
We’ve started selling USB versions of these two RoboClaw motor controllers from Orion Robotics:
These new RoboClaws add a USB serial interface to the other three control interfaces available (TTL serial, RC, and analog inputs), but are otherwise identical to the V4 RoboClaw 2×15A and 2×30A controllers that we previously offered. Like their predecessors, they can drive a pair of brushed DC motors with up to 15 A or 30 A, respectively, at voltages from 6 V to 34 V. Integrated dual quadrature decoders make it easy to create a closed-loop speed control system; analog feedback is also supported for closed-loop position control.
We have added a compact, powerful new NEMA 17-size stepper motor to our wide selection of stepper motors. This 42×38 mm stepper motor is available with a standard 5 mm D-shaft for general-purpose use, but perhaps more exciting is the version with a 28 cm threaded rod, which turns it into a linear actuator capable of precision open-loop position control. This latter version has the stainless steel lead screw built right into the stepper motor, so there is no need to deal with extra hardware such as shaft couplers and set screws, and the copper alloy traveling nut with mounting holes is included. Raise your next project to new heights with the precision (40 µm per full step) and control of a stepper motor!
Please see the product pages for more information:
- Stepper Motor: Bipolar, 200 Steps/Rev, 42×38mm, 2.8V, 1.7 A/Phase
- Stepper Motor with 28cm Lead Screw: Bipolar, 200 Steps/Rev, 42×38mm, 2.8V, 1.7 A/Phase
For other options, you can take a look at our full selection of stepper motors.
This data logger shield from Adafruit provides an easy way for your Arduino to save data so you can process and analyze it later. It accepts any SD card formatted with a FAT16 or FAT32 file system, and it includes a real-time clock (RTC) for accurate timestamping of your data. Lots of documentation and resources are available from Adafruit to help you get started with the shield.
For more information, see the Adafruit Data Logging Shield for Arduino product page.
This UL-certified AC-to-DC converter gives you an easy way to deliver up to 1 A to your USB-powered device from a US-style AC electrical socket. It has been specifically designed to supply 5.25 V instead of 5 V to help ensure that the device it is powering receives close to 5 V even when the current draw is high. This converter is safe for use with USB-compliant devices.
This adapter does not include a USB cable, but it features a USB “A” port that you can plug a standard USB cable into, which makes it great for transitioning your project from USB to wall power.
For more information, see the 5V wall power adapter product page.
The Hydra is a triple-output power converter from CH Robotics designed to make it easier to get the power you need for your next project. The Hydra can quickly give you access to three independent, software-configurable DC output voltages to power your system. The easy-to-use Smart Power Supply Control Software makes it quick and simple to configure and control the Hydra’s outputs from your computer via USB. Bench-top power supplies can be large and bulky, but the Hydra fits in the palm of your hand and can also be configured from a user-programmable microcontroller via serial. This flexibility makes the Hydra a great fit for a large variety of projects, whether you are building an industrial system or a small mobile robot.
For more information, see the Hydra product page.