The Imperfect Bipolar Transistor

April 16, 2021 by Al Williams 15 Comments

We like to pretend that our circuit elements are perfect because, honestly, it makes life easier and it often doesn’t matter much in practice. For a normal design, the fact that a foot of wire has a tiny bit of resistance or that our capacitor value might be off by 10% doesn’t make much difference. One place that we really bury our heads in the sand, though, is when we use bipolar transistors as switches. A perfect switch would have 0 volts across it when it is actuated. A real switch won’t quite get there, but it will be doggone close. But a bipolar transistor in saturation won’t be really all the way on. [The Offset Volt] looks at how a bipolar transistor switches and why the voltage across it at saturation is a few tenths of a volt. You can see the video below.

To understand it, you’ll need a little bit of math and some understanding of the construction of transistors. The idea of using a transistor as a switch is that the transistor is saturated — that is, increasing base current doesn’t make much change in the collector current. While it isn’t perfect, it is good enough to switch a relay or do other common switching tasks.

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Detergent DRM Defeated On Diminutive Dishwasher

April 16, 2021 by Dan Maloney 71 Comments

Has it really come to this? Are we really at the point that dishwashers have proprietary detergent cartridges that you’re locked into buying at inflated prices?

Apparently so, at least for some species of the common kitchen appliance. The particular unit in question goes by the friendly name of Bob, and is a compact, countertop unit that’s aimed at the very small kitchen market. [dekuNukem] picked one of these units up recently, and was appalled to learn that new detergent cartridges would cost an arm and a leg. So naturally, he hacked the detergent cartridges. A small PCB with an edge connector and a 256-byte EEPROM sprouts from each Bob cartridge; a little reverse engineering revealed the right bits to twiddle to reset the cartridge to its full 30-wash count, leading to a dongle to attach to the cartridge when it’s time for a reset and a refill.

With the electronics figured out, [dekuNukem] worked on the detergent refill. This seems like it was the more difficult part, aided though it was by some fairly detailed specs on the cartridge contents. A little math revealed the right concentrations to shoot for, and the ingredients in the OEM cartridges were easily — and cheaply — sourced from commercial dishwashing detergents. The cartridges can be refilled with a properly diluted solution using a syringe; the result is that each wash costs 1/75-th of what it would if he stuck with OEM cartridges.

For as much as we despise the “give away the printer, charge for the ink” model, Bob’s scheme somehow seems even worse. We’ve seen this technique used to lock people into everything from refrigerator water filters to cat litter, so we really like the way [dekuNukem] figured everything out here, and that he saw fit to share his solution.

You Need An Automated Overhead Camera Assistant

April 14, 2021 by Kristina Panos 13 Comments

It’s 2021. Everyone and their mother is filming themselves doing stuff, and a lot of it is super cool content. But since most of us have to also work the video capture devices ourselves, it can be difficult to make compelling footage with a single, stationary overhead view, especially when there are a lot of steps involved. A slider rig is a good start, but the ability to move the camera in three dimensions programmatically is really where it’s at.

[KronBjorn]’s excellent automated overhead camera assistant runs on an Arduino Mega and is operated by typing commands in the serial monitor. It can pan ±20° from straight down and moves in three axes on NEMA-17 stepper motors. It moves really smoothly, which you can see in the videos after the break. The plastic-minimal design is interesting and reminds us a bit of an ~~ophthalmoscope~~ phoropter — that’s that main rig at the eye doctor. There’s only one thing that would make this better, and that’s a dedicated macro pad.

If you want to build your own, you’re in luck — there’s quite a lot of detail to this project, including a complete BOM, all the STLs, code, and even assembly videos of the 3D-printed parts and the electronics. Slide past the break to check out a couple of brief demo videos.

Not enough room for a setup like this one? Try the pantograph version.

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Gaming With 1 Horsepower Of Rumble Feedback

April 14, 2021 by Lewin Day 14 Comments

Force feedback took off in a big way in the late 90s, bringing a sense of realism to flight sticks and racing wheels that hadn’t been there before. Its cheaper haptic cousin was rumble feedback via vibration motors, which does add a little something but it’s more an idea of a feeling than anything relevant to real life. It’s also usually pretty weak, but [teenenggr] has a way around that.

The build takes a regular Playstation controller, and disconnects the internal rumble motors. The controller’s motor output is instead linked to an Arduino Uno’s digital input. When the Arduino detects the rumble motor signal switching on, it turns on a relay, supplying power to a hefty one horsepower induction motor, fitted with an eccentric weight.

What happens next is pure chaos. Essentially equivalent to throwing a brick in a washing machine, the motor shakes the entire desk at the slightest hint of rumble signals from the gain. Sustained vibration commands, such as when firing machine guns in Crysis, flung [teenenggr]’s monitor from the desk. Even with it taped down, game play quickly became impossible as he inadvertently hits ALT-Tab and leaves the game while trying to hang on to the desk for dear life.

Is it a useful hack? No, but it would make an excellent prank if bolted underneath your friend’s gaming rig for a laugh. With that said, the intense vibration probably won’t do any good for mechanical hard drives, anything with edge connectors, or just their computer in general. It’s a big step up from the last [teenenggr] project we featured – a rumble feedback mouse. Video after the break.
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Sanity Check Your Engines With This Dynamometer

April 14, 2021 by Sonya Vasquez 2 Comments

As you get ready to pop the hood of your RC car to drop in a motor upgrade, have you ever wondered how much torque you’re getting from these small devices? Sure, we might just look up the motor specs, but why trust the manufacturer with such matters that you could otherwise measure yourself? [JohnnyQ90] did just that, putting together an at home-rig built almost from a stockpile of off-the-shelf parts.

To dig into the details, [JohnnyQ90] has built himself a Prony Brake Dynamometer. These devices are setup with the motor shaft loosely attached to a lever arm that can push down on a force-measuring device like a scale. With our lever attached, we then power up our motor. By gradually increasing the “snugness” of the motor shaft, we introduce sliding friction that “fights” the motor, and the result is that, at equilibrium, the measured torque is the maximum amount possible for the given speed. Keep turning up that friction and we can stall the motor completely, giving us a measurement of our motor’s stall torque.

Arming yourself with a build like this one can give us a way to check the manufacturer’s ratings against our own, or even get ratings for those “mystery motors” that we pulled out the dumpster. And [JohnnyQ90’s] build is a great reminder on how we can leverage a bit of physics and and a handful of home goods to get some meaningful data.

But it turns out that Prony Brake Dynamometers aren’t the only way of measuring motor torque. For a disc-brake inspired, have a look at this final project. And if you’re looking to go bigger, put two motors head-to-head to with [Jeremy Felding’s] larger scale build.

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New HackadayU Classes: Antenna Basics, Raspberry Pi Pico, And Designing Complex Geometry

April 13, 2021 by Mike Szczys 4 Comments

Get ’em while they’re hot: a new session of HackadayU just opened with classes from three fantastic instructors and seats are filling up fast.

Introduction to Antenna Basics — Instructor Karen Rucker teaches the fundamentals of antenna design as if it were your first year on-the-job. She’ll cover the common types of antenna designs and the fundamentals of radio frequency engineering that go into them. Begins Thursday, May 6th.

Raspberry Pi Pico and RP2040 – The Deep Dive — Instructor Uri Shaked guides the class through the internals of the RP2040 microcontroller, covering system architecture, hardware peripherals, and dipping into some ARM assembly language examples. Begins Wednesday, May 5th.

Designing with Complex Geometry — Instructor James McBennett helps you up your 3D modelling game with a course on using complex geometries in Grasshopper3D (part of Rhino3D). Dive into Non-uniform rational B-spline (NURBS) and go from simple shapes to incredibly complex objects with a bit of code. Begins Tuesday, May 4th.

Each course includes five weekly classes beginning in May. Being part of the live class via Zoom offers interactivity with the instructor and other attendees. All tickets are “pay-as-you-wish” with a $20 suggested donation; all proceeds go to socially conscious charities.

For the benefit of all, each class will be edited and published on Hackaday’s YouTube channel once this session has wrapped up. Check out our playlists for past HackadayU courses, or watch them all in one giant playlist.

You might also consider becoming an Engineering Liaison for HackadayU. These volunteers help keep the class humming along for the best experience for students and instructors alike. Liaison applications are now open.

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Alien Art Drawn With Surprisingly Simple Math

April 13, 2021 by Michael Shaub 20 Comments

Programmer [aemkei] Tweeted the formula (x ^ y) % 9 alongside code for more “alien art”. But how can a formula as simple as (x ^ y) % 9 result in a complex design? The combination of Bitwise XOR (^) and Modulo (%) generate a repeating pattern that’s still complex enough to satisfy the eye, and it’s ok if that doesn’t sound like an explanation. Bitwise operations are useful when working with memory and shift registers, but also worth learning if you want to drive lines or matrices of LEDs or interpret combinations of multiple switches, or in this case a great way to throw an interesting test pattern up on a new flip-dot display or low-res LED matrix. Are you into it? We are, so let’s jump in.

XOR Truth Table
	0b00	0b01	0b10	0b11
0b00	0b00	0b01	0b10	0b11
0b01	0b01	0b00	0b11	0b10
0b10	0b10	0b11	0b00	0b01
0b11	0b11	0b10	0b01	0b00

Bitwise XOR compares each binary digit of the two inputs. The XOR returns a 1 when only one of the two digits is a 1, otherwise, it returns a zero for that position. Let’s say the coordinates were 3, 2. Converted to binary we have 0b11 and 0b10. From this truth table, we can see the most-significant digits are both 1, returning a 0, while only one of the least-significant digits is a 1, so the comparison returns a 1.

Moving onto the %, which is the Modulo operator has nothing to do with percentages. This operator divides two numbers and returns the remainder if any. Take 9 % 5. When dividing 9 by 5, 5 goes in once with a remainder of 4 so 9 % 5 = 4. Now our original formula from the top will draw a black box for every ninth number except that the bitwise XOR throws a wrench into that count, varying how often a number divisible by 9 appears and supplying the complexity necessary for these awesome patterns.