# Pololu Blog

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.

# SK9822 LED jack-o-lantern

Posted by Jon on 15 October 2018

To kick off our 2018 mini-series of spooky Halloween projects, I’ll go over how I fixed and modified my family’s broken light-up jack-o-lantern, but first I want to remind you that our Halloween sale is still going on. Visit the sale page for more information, and if you are in need of some inspiration, check out our Halloween-tagged blog posts for some sample projects. Now, on to the jack-o-lantern…

The lantern suffered from a couple of burnt out incandescent bulbs and an unreliable power switch. The switch had a poor mechanical connection somewhere, which meant that in addition to sliding it into the “on” position, the case had to be pressed/squeezed in just the right spot to connect power. I absolutely needed to replace the switch, but in addition, this was a good time to upgrade from a bland set of incandescent lights to a more customizable lighting solution by adding some individually addressable RGB LEDs.

I wanted to preserve the battery-powered functionality of the lantern, and since it is powered by 4 C batteries, it has a supply voltage that could be anywhere between about 4V and 6V. The SK9822 LED strips that I wanted to use run on 5V, so I would need some kind of regulator to power them, as well as a microcontroller to send them control signals. Fortunately, our A-Star Mini microcontrollers have onboard regulators that allow them to work with a wide operating range of voltages, and provide ample current that can be used for other devices in the system, like the SK9822. In particular, the A-Star Mini LV was a good fit for a system like this with a voltage that started above 5V and could drop below it as the batteries were drained. (That A-Star’s regulator can also provide about 1A of current!)

Starting the upgrade was pretty straightforward: remove all of the old hardware (the mess of old rusty wiring, the incandescent bulbs, and the switch), and solder in the A-Star to the battery holder terminals. From there, I soldered in a rocker switch that was much more satisfying to flip on and off than the older nonworking slide switch. Finally, I soldered up the four connections to the LED strip.

The strip itself only used 4 LEDs, since the lantern illuminates well and I didn’t want to unnecessarily consume lots of power (especially because the lantern was battery powered). The 4 piece segment was cut from one of the low density 30 LEDs per meter strips. The lower density meant that the LEDs were spaced out farther apart, which was useful to spread the LEDs across the plastic tube on the inside of the lantern and more evenly distribute the light. Our LED strip library made it easy to get started programming!

Another benefit of this hardware upgrade is the ability to reprogram the lighting display to whatever I want. Also, since the LED strips use so few IO pins, the decoration is in a good state to add additional electronics (like a proximity sensor or MP3 trigger)!

# Polo-BOO! Halloween Sale

Posted by Ben on 10 October 2018

Looking to make an awesome Halloween costume or impressive yard display? Well, we want to help, so we’re having a sale through Wednesday, October 24 on hundreds of items you can use to make things that will impress or terrify your friends and neighbors! Visit the sale page for more information, and if you are in need of some inspiration, check out our Halloween-tagged blog posts for some sample projects.

By the way, we’d love to see more about the amazing things you all are building with our products, so please don’t hesitate to share them with us!

# New product: Mounting Bracket for Standard-Size Servos

Posted by Brandon on 1 October 2018
Tags: new products

We now have a new mounting bracket available, this time designed for standard-size servos. Servos are very versatile and often make for an easy way to add precise motion to your project, but they can sometimes be difficult to mount due to their shape and the orientation of their intended mounting holes. Our new Mounting Bracket for Standard-Size Servos aims to solve that problem.

Instead of using the servo’s intended mounting holes, this bracket clasps around the servo, capturing its mounting tabs and providing an easy way to mount a servo on its side. The mounting holes on the bracket are intended for use with M3 or #4 screws (sold separately).

As with the Romi Expansion Plate we just released, this bracket was originally designed as part of our Robot Arm Kit for Romi.

# New product: Romi Chassis Expansion Plate

Posted by Brandon on 21 September 2018
Tags: new products

The Romi Chassis Expansion Plate is now available and is a great way to add even more space to the Romi. It is designed to function as a modular expansion option for the Romi. In fact, if you have been following our new product announcements, you might have already seen this plate as part of the Robot Arm Kit for Romi. The expansion plate is a half circle with the same diameter as the Romi base plate, and it can be installed over either the front or rear half of the Romi chassis. Abundant mounting holes and slots cover the plate, matching the pattern used on the Romi chassis base plate and supporting various sizes of screws.

You can combine two plates to make a full-sized platform.

It is also possible to stack multiple expansion plates for even more versatility.

# New products: 1- and 31-channel QTR HD reflectance sensor arrays

Posted by Jan on 31 August 2018

This week, we released what we expect to be the extremes of our new line of QTR HD reflectance sensor arrays, with two sizes of a single-sensor board on the small end and a massive 31-sensor array for the maximum size. This picture shows the relative sizes of the boards, along with some of the intermediate sizes we have available:

We made the two single-sensor sizes because we could make good arguments for each one. Part of the point of doing a single-sensor board is to make it really small, so you can fit it into tight spaces. But “really small” means different things depending on the dimensions you care about. So we have one version that is only 5 mm (0.2") wide, with components on both sides of the PCB, and one version that is 7.5 mm (0.3") wide, with components on just one side. The 7.5 mm wide version is a little thinner and flatter because it doesn’t have parts on one side, can be used with a 3×1, single row connector, and costs slightly less because of the single-sided assembly.

As I mentioned in some of my earlier posts (here and here) about this new line of sensor arrays, we are using two sensor types: more economical units we are calling “QTR”, and higher-performance units with lenses that we are calling “QTRX”. The main appeal of the QTRX sensors is that they can give the same readings at much lower IR emitter currents, which can really make a big difference for big sensor arrays. But if you crank up the current in those QTRX sensors, you can also get more distance. We did not do that on the QTRX arrays because the sensor modules leak light out the sides and interfere with each other when they are closely spaced, but with these single-channel boards, we are also making available the QTRX sensors with the higher 30 mA maximum emitter current, which allows for a range of up to about 8 cm (about 3 inches). We are calling these sensors QTRXL.

This video (taken with an old camera that does not have as much IR filtering as most newer cameras) shows the IR light leakage around the side of the QTRX sensor module:

I should point out that all of these new QTR modules offer variable brightness control by varying the current through the emitter using the control pin. However, if you want to take advantage of the maximum brightness and range, and have several sensors close to each other, you will need some barriers between them to prevent them from blinding each other (or just turn on one emitter at a time).

The 31-sensor arrays are huge! Well, at least compared to the tiny single-sensor boards.

The routing on those boards is quite complex because adjacent IR emitters are not just wired in series (because we want to have separate even/odd emitter control, plus the alternate density population options I discussed in this post), so we ended up having to go to a 4-layer PCB to route it. This did let us make the vertical dimension a little lower, so the board is just 16.5 mm tall, compared to the 20 mm board height for the versions with 15 and fewer sensors. The 31-channel board is also 0.062" (1.6 mm) thick, compared to the thinner 0.040" (1 mm) boards we use for the lower channel counts. You can compare all the dimensions of the various boards in the detailed dimension diagram (1MB pdf).

The sixteen new boards we released this week brings the total available in this new QTR HD product line to 40. You can see the options neatly summarized in the tables below to pick the best array for your application.

QTR sensors
2.9 V to 5.5 V; 30 mA max LED current(1); 5 mm optimal range
Board
width
Configuration Max board
current(2)
Max range Output
type
Name 1-piece
price
5.0 mm 1 sensor (HD)
32 mA 30 mm analog QTR-HD-01A $1.79 RC (digital) QTR-HD-01RC 7.5 mm 1 sensor (MD) 32 mA 30 mm analog QTR-MD-01A$1.61
RC (digital) QTR-MD-01RC
10.2 mm 4 mm × 2
32 mA 30 mm analog QTR-HD-02A $2.12 RC (digital) QTR-HD-02RC 17.0 mm 4 mm × 4 62 mA 40 mm analog QTR-HD-04A$3.26
RC (digital) QTR-HD-04RC
29.0 mm 8 mm × 4
62 mA 40 mm analog QTR-MD-04A $3.44 RC (digital) QTR-MD-04RC 4 mm × 7 125 mA 40 mm analog QTR-HD-07A$5.40
RC (digital) QTR-HD-07RC
61.0 mm 8 mm × 8
125 mA 40 mm analog QTR-MD-08A $6.39 RC (digital) QTR-MD-08RC 4 mm × 15 250 mA 50 mm analog QTR-HD-15A$10.82
RC (digital) QTR-HD-15RC
125.0 mm 4 mm × 31
495 mA 50 mm analog QTR-HD-31A $21.66 RC (digital) QTR-HD-31RC QTRX sensors 2.9 V to 5.5 V; 3.5 mA max LED current(1); 10 mm optimal range Board width Configuration Max board current(2) Max range Output type Name 1-piece price 5.0 mm 1 sensor (HD) 5 mA 30 mm analog QTRX-HD-01A$2.17
RC (digital) QTRX-HD-01RC
7.5 mm 1 sensor (MD)
5 mA 30 mm analog QTRX-MD-01A $1.99 RC (digital) QTRX-MD-01RC 10.2 mm 4 mm × 2 5 mA 30 mm analog QTRX-HD-02A$2.88
RC (digital) QTRX-HD-02RC
17.0 mm 4 mm × 4
9 mA 40 mm analog QTRX-HD-04A $4.78 RC (digital) QTRX-HD-04RC 29.0 mm 8 mm × 4 9 mA 40 mm analog QTRX-MD-04A$4.96
RC (digital) QTRX-MD-04RC
4 mm × 7
17 mA 40 mm analog QTRX-HD-07A $8.06 RC (digital) QTRX-HD-07RC 61.0 mm 8 mm × 8 17 mA 40 mm analog QTRX-MD-08A$9.43
RC (digital) QTRX-MD-08RC
4 mm × 15
34 mA 50 mm analog QTRX-HD-15A $16.52 RC (digital) QTRX-HD-15RC 125.0 mm 4 mm × 31 68 mA 50 mm analog QTRX-HD-31A$33.44
RC (digital) QTRX-HD-31RC
QTRXL sensors
2.9 V to 5.5 V; 30 mA max LED current(1); 20 mm optimal range
Board
width
Configuration Max board
current(2)
Max range Output
type
Name 1-piece
price
5.0 mm 1 sensor (HD)
32 mA 80 mm analog QTRXL-HD-01A $2.17 RC (digital) QTRXL-HD-01RC 7.5 mm 1 sensor (MD) 32 mA 80 mm analog QTRXL-MD-01A$1.99
RC (digital) QTRXL-MD-01RC
1 Can be dynamically reduced to any of 32 available dimming levels.
2 With all LEDs on at max brightness setting.

Our introductory promotions are still going strong! Be one of the first 100 customers to use coupon code QTRINTRO and get any of these new sensors at half price! (Limit 3 per item per customer.)

# New products: Robot Arm Kit for Romi (and also just the gripper)

Posted by Jan on 30 August 2018

I’m super excited to announce our newest product, the Robot Arm Kit for Romi. The Romi arm is designed to mount to the back half of a Romi chassis with two fixed servos controlling the height and angle of the gripper through a nifty linkage system.

The gripper itself uses a micro servo with two parallel fingers or paddles that open and close through a rack and pinion arrangement. Here is a quick video demonstration of a Romi chassis with the arm attachment:

You can see the available range of motion in the drawings below:

The kit ships with all mechanical parts, including special servos with a fourth wire for reading the position of the output shaft:

We are also making the gripper used on the arm available as a standalone Micro Gripper Kit with Position Feedback Servo. Here is a picture of the assembled gripper:

Products like this arm kit, with many injection-molded components, are some of the most complicated and time-consuming products we make. As those of you who have followed our growth over the past decade are probably aware, we try to develop our more complete robot kits incrementally, starting with components like just a wheel or a motor bracket, and then using those components in the more integrated robots. For example, we came out with this line of wheels in 2010:

The Romi and Balboa robots, which use those wheels, did not come out until 2016 and 2017.

If you look at the parts that go into just the gripper portion, you can see that each of the components is roughly as complicated as one of those wheels, and you can’t really do much with just one of those parts:

So, a lot of work goes into designing these kits. We also do not machine the molds or do the injection molding in-house (we did that on the first few parts for the 3pi robot), so that adds a lot of delays compared to our electronics boards, which we make in the same building that we design them in. We do 3D print prototypes to maximize the chances that we get the designs right, but there are invariably little modifications that we end up having to make when the components are this complicated, which is why it takes us years to go from the initial idea to the released kit.

We are at least sticking to our incremental product release approach as far as integration with electronics goes: at the time of the Romi arm attachment release, we do not have a specific solution for controlling the robot, which we will be working on next. Therefore, this kit is currently intended for advanced users who are comfortable powering and controlling several servos on their own.

As with all of our new product releases this year, we are offering substantial introductory discounts for the first customers to try out our new designs. You can use coupon code ROMIARMINTRO to get the whole arm for just $49 and code GRIPPERINTRO to get just the gripper for only$13. Each coupon is limited to 100 uses and 3 units per customer.

(702) 262-6648
Same-day shipping, worldwide