Stepper Motor? Encoder? It’s Both!

July 15, 2018 by Al Williams 22 Comments

We always think it is interesting that a regular DC motor and a generator are about the same thing. Sure, each is optimized for its purpose, but inefficiencies aside, you can use electricity to rotate a shaft or use a rotating shaft to generate electricity. [Andriyf1] has a slightly different trick. He shows how to use a stepper motor as an encoder. You can see a video of the setup below.

It makes sense. If the coils in the stepper can move the shaft, then moving the shaft should induce a current in the coils. He does note that at slow speeds you can miss pulses, however. Again, the device isn’t really optimized for this type of operation.

The circuit uses an opamp-based differential amplifier to read the pulses from the coil. Two opamps on two coils produce a quadrature signal just like a normal encoder. When the shaft turns in one direction, one pulse will lead the other. In the other direction, the lead pulse will be reversed.

There’s code to let an Arduino read the pulses. And here’s plenty of code that will read quadrature on an Arduino or other processors. We’ve seen similar hacks done with hard drive motors which are quite similar, by the way.

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Mademoiselle Pinball Table Gets Rock ‘n Roll Makeover

July 13, 2018 by Kristina Panos 11 Comments

Once upon a time, there was a music venue/artist collective/effects pedal company that helped redefine industry in Williamsburg, Brooklyn. That place was called Death By Audio. In 2014, it suffered a death by gentrification when Vice Media bought the building that DBA had worked so hard to transform. From the ashes rose the Death By Audio Arcade, which showcases DIY pinball cabinets made by indie artists.

Their most recent creation is called A Place To Bury Strangers (APTBS). It’s built on a 1959 Gottlieb Mademoiselle table and themed around a local noise/shoegaze band of the same name that was deeply connected to Death By Audio. According to [Mark Kleeb], this table is an homage to APTBS’s whiz-bang pinball-like performance style of total sensory overload. Hardly a sense is spared when playing this table, which features strobe lights, black lights, video and audio clips of APTBS, and a fog machine. Yeah.

[Mark] picked up this project from a friend, who had already cut some wires and started hacking on it. Nearly every bit of the table’s guts had to be upgraded with OEM parts or else replaced entirely. Now there’s a Teensy running the bumpers, and another Teensy on the switches. An Arduino drives the NeoPixel strips that light up the playfield, and a second Uno displays the score on those sweet VFD tubes. All four micros are tied together with Python and a Raspi 3.

If you’re anywhere near NYC, you can play the glow-in-the-dark ball yourself on July 15th at Le Poisson Rouge. If not, don’t flip—just nudge that break to see her in action. Did we mention there’s a strobe light? Consider yourself warned.

Want to get into DIY pinball on a smaller scale? Build yourself a sandbox and start playing.

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Supersize DIY R/C Servos From Windscreen Wipers

July 13, 2018 by Ben James 26 Comments

We’re all familiar with the experience of buying hobby servos. The market is awash with cheap clones which have inflated specs and poor performance. Even branded servos often fail to deliver, and sometimes you just can’t get the required torque or speed from the small form factor of the typical hobby servo.

Enter [James Bruton] and his DIY RC servo from a windscreen wiper motor. Windscreen wiper motors are cheap as chips, and a classic salvage. The motor shaft is connected to a potentiometer via a pulley and some string, providing the necessary closed-loop feedback. Instead of using the traditional analog circuitry found inside a servo, an Arduino provides the brains. This means PID control can be implemented on the ‘duino, and tuned to get the best response from different load characteristics. There’s also the choice of different interfacing options: though [James]’ Arduino code accepts PWM signals for a drop-in R/C servo replacement, the addition of a microcontroller means many other input signal types and protocols are available. In fact, we recently wrote about serial bus servos and their numerous advantages.

We particularly love this because of the price barrier of industrial servomotors; sure, this kind of solution doesn’t have the precision or torque that off-the-shelf products provide, but would be sufficient for many hacks. Incidentally, this is what inspired one of our favourite open source projects: ODrive, which focuses on harnessing the power of cheap brushless motors for industrial use.

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Morphing Digital Clock Will Show You A Good Time

July 10, 2018 by Kristina Panos 27 Comments

A few weeks ago, [HariFun] set out to emulate a 7-segment display with an LED matrix. Seems easy enough, right? Right. He also wanted to come up with a new way to transition between digits, which is a much harder task. But he did it, and it’s really cool. At a viewer’s suggestion, [Hari] used the transition as the basis for a mesmerizing clock that brings the smooth sweep of an analog second-hand into the digital age.

This is the coolest way to watch the time pass since the hourglass. You can almost hear the light move as one digit slides into the next. Each transition is totally unique, so depending on the digit this involves one or more vertical segments sliding from right to left, or multiple segments moving in a counter-clockwise circle.

You too can watch time glide by with little more than a 64×32 RGB LED matrix, a NodeMCU, and [Hari]’s digit transition code. It only costs about $25 to build, and you really can’t beat the quality of instruction he’s put together. Take a second or two and check it out after the break.

If you prefer OLEDs and vertical transitions, there’s a clock for that, too.

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Vintage Headphones Bluetooth Conversion Goes The Extra Mile

July 9, 2018 by Ben James 2 Comments

[KaZjjW] wanted to retrofit a pair of nicely styled vintage headphones to be able to play wirelessly over Bluetooth. In principle this is an easy task: simply stick a Bluetooth audio receiver on the line-in, add a battery, and you’re all set. However, [KaZjjW] wanted to keep the aesthetic changes to the headphones at an absolute minimum, retaining the existing casing and volume control, whilst cramming the electronics entirely inside and out of sight.

With the inherent space constraints inside the cups of the headphones, this proved to be quite a challenge. The existing volume potentiometer which hung half outside the case was remounted on an ingenious hinge made of two PCBs, with the pot floating next to a surface mounted switch. This allowed it to not only control the volume, but also act as an on/off switch for the Bluetooth. The only other existing cuts in the casing were a circular hole for the audio cable, and a slit for the cable strain relief. These worked perfectly for an LED status indicator and micro-USB battery charging.

The main chip used for receiving audio over Bluetooth was the BM62 by Microchip. It’s a great all-in-one solution for this kind of project as it has built-in battery charging, an on-board DAC and audio amp, as well as a serial control interface. In part 2 of the project log, the process of programming the BM62 was documented, and it was painful – it’s a shame that the software support lets it down. But a hacker will always find a way, and we’ve seen some pretty neat hacks for reprogramming existing chips in off-the-shelf Bluetooth headphones.

Two PCBs for the pot button hinge, one for the LED and micro-USB connector, as well as one for the Bluetooth receiver and a PIC. That’s four PCBs in a pretty small space, enabled by some commendable design effort both electronically and mechanically. It certainly paid off, as the finished product looks very slick.

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A Peek Into A Weed-Eating Robot’s Test Fixtures

July 7, 2018 by Donald Papp 2 Comments

When it comes to production, fast is good! But right the first time is better. Anything that helps prevent rework down the line is worth investing in. Some of the best tools to catch problems are good test fixtures. The folks at Tertill (a solar-powered robot for killing weeds that kickstarted last year) took the time to share two brief videos of DIY test fixtures they use to test components before assembly.

The videos are short, but they demonstrate all the things that make a good test: on the motor tester there are no connectors or wires to fiddle with, the test starts automatically, and there is clear feedback via prominent LEDs. The UI board tester also starts automatically and has unambiguous LED feedback, and sports a custom board holder with a recess just the right shape for the PCB. Once the board is in, the sled is pushed like a drawer to make contact with the test hardware and begin the test. The perfectly formed recesses in both units serve another function as well; they act as a go/no-go test for the physical shape of the components and contacts being tested.

Both videos are embedded below; and while there isn’t much detail on the actual test hardware, we do spy a Raspberry Pi and at least two Adafruit logos among other hacker-familiar elements like laser-cut acrylic, 3D printed plastic, pogo pins, and a PVC junction box.

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Junk Bin Self Balancing Bot With ESP8266

July 5, 2018 by Tom Nardi 10 Comments

As we all know, sometimes the projects we plan simply never materialize. You have an idea, maybe even buy some of the parts you need, and then…nothing. Maybe you changed your mind, or maybe the idea was never that good to begin with. In any event, time marches on, the parts pile up, and the ideas come and go. Such is the life of the hacker.

[Andrius Mikonis] writes in to tell us how his graveyard of abandoned projects ended up providing exactly what he needed to embark on a project he’s been fascinated with for years: the two-wheel self balancing robot. He started with a motor and wheel set that was originally intended to be part of a rover, added an accelerometer, and tied the whole thing together with an ESP-01 he had lying around. The final result certainly looks the part, and goes to show that projects don’t always need to be 1000 hour labors of love to accomplish their goals.

The construction of this little bot is simple in the extreme. A piece of plywood makes up the primary structure, with the wheels glued to the bottom and the electronics taking up residence in the top. It’s powered by two lithium battery cells that were salvaged out of an old laptop, with a DC-DC buck converter to provide a stable 3.3 VDC for the ESP-01 and MPU6050 accelerometer. To control the motors themselves, [Andrius] is using a cheap L293 controller that he found on eBay.

For interactive control, [Andrius] is making use of the ESP’s Wi-Fi to provide a web-based interface. This lets you control the bot from essentially any device that has a browser, rather than having to use a dedicated hardware transmitter.

Self-balancing robots of various levels of complexity are a relatively common project in the hacker world. There’s just something magical about the way they scoot around, seeming to defy gravity.