Hands can grab things, build things, communicate, and we control them intuitively with nothing more than a thought. To those who miss a hand, a prosthesis can be a life-changing tool for carrying out daily tasks. We are delighted to see that [Alvaro Villoslada] joined the Hackaday Prize with his contribution to advanced prosthesis technology: Dextra, the open-source myoelectric hand prosthesis.
Dextra is an advanced robotic hand, with 4 independently actuated fingers and a thumb with an additional degree of freedom. Because Dextra is designed as a self-contained unit, all actuators had to be embedded into the hand. [Alvaro] achieved the necessary level of miniaturization with five tiny winches, driven by micro gear motors. Each of them pulls a tendon that actuates the corresponding finger. Magnetic encoders on the motor shafts provide position feedback to a Teensy 3.1, which orchestrates all the fingers. The rotational axis of the thumb is actuated by a small RC servo.
In addition to the robotic hand, [Alvaro] is developing his own electromyographic (EMG) interface, the Mumai, which allows a user to control a robotic prosthesis through tiny muscle contractions in the residual limb. Just like Dextra, Mumai is open-source. It consists of a pair of skin electrodes and an acquisition board. The electrodes are attached to the muscle, and the acquisition board translates the electrical activity of the muscle into an analog voltage. This raw EMG signal is then sampled and analyzed by a microcontroller, such as the ESP8266. The microcontroller then determines the intent of the user based on pattern recognition. Eventually this control data is used to control a robotic prosthesis, such as the Dextra. The current progress of both projects is impressive. You can check out a video of Dextra below.
In this day and age we’re consistently surrounded with portable electronic devices. In order for them to be called “portable”, they must run on batteries. Most, if not all, use rechargeable batteries. These batteries have a finite lifespan, and will eventually need to be replaced. UCI chemist [Reginald Penner] and doctoral candidate [Mya Le Thai] have been hard at work on making rechargeable batteries that last forever.
Nanowires are great candidates for rechargeable battery technology because the wires, thousands of times thinner than a human hair, are great conductors of electricity. The problem is repeated charging and discharging makes them brittle, which causes them to eventually fail. Typically, the researchers at UCI could get 5000 to 7000 cycles in before they failed. After some trial and error, they found that if they coat a gold nanowire with an acrylic-like gel, they can get up to 200,000 charge/discharge cycles through it before failure.
Before the Commodore 64, the IBM PC, and even the Apple I, most computers took input data from a type of non-magnetic storage medium that is rarely used today: the punched card. These pieces of cardstock held programs, data, and pretty much everything used to run computers in the before-time. But with all of that paper floating around, how did a programmer or user keep up with everything? Enter the punch card sorter and [Ken Shirriff[‘s eloquent explanation of how these machines operate.
Card sorters work by reading information on the punched card and shuffling the cards into a series of stacks. As [Ken] explains, the cards can be run through the machine multiple times if they need to be sorted into more groups than the machine can manage during one run, using a radix sort algorithm.
The card reader that [Ken] examines in detail uses vacuum tubes and relays to handle the logical operation to handle memory and logic operations. This particular specimen is more than half a century old, rather robust, and a perfect piece for the Computer History Museum in Mountain View.
It’s always interesting to go back and examine (mostly) obsolete technology. There are often some things that get lost in the shuffle (so to speak). Even today, punched cards live on in the automation world, where it’s still an efficient way of programming various robots and other equipment. Another place that it lives on is in voting machines in jurisdictions where physical votes must be cast. Hanging chads, anyone?
Crystal radios are old news, but great fun. What would happen if a PhD designed a crystal set? By PhD we mean Pizza Hut Deliveryperson and [John Greenlee] (who may not actually be a PhD of either kind; we don’t know) gives us a good idea with his crystal radio in a pizza box.
Pizza boxes aren’t the only food-related material in this radio. [John] makes a tuning capacitor out of cake rounds. Coincidentally, he decorates the tuning capacitor to look like a pizza.
The schematic itself is unremarkable–just a common crystal set. But the construction of the chassis and the capacitor make it an interesting project. If you know a young person that has any interest in radio, a crystal receiver is a rite of passage you shouldn’t deny them and this one is certainly a novelty. The picture of a pizza takes it even one step further than this YouTube build, which is nonetheless a good resource.
The instructions are well done, although some of the parts may be slightly hard to find. Germanium diodes and high-Z earphones are not as plentiful as they used to be, although you can still find them if you look.
Last weekend was Hamvention, the place you want to be on the third weekend in May. It is the world’s largest gathering of amateur radio enthusiasts, and an exceedingly large flea market containing all sorts of electronica.
The booths of Hamvention include a few notable Open Hardware folk, but for the most part, you’re looking a few big booths from Yaesu, an entire section dedicated to everything ARRL, and a few pop-ups from the usual suspects. Rigol was there, showing off their test equipment and selling the DS1052E oscilloscope for far more than it’s worth. The Rigol Zed is a much better buy, anyway.
As with any gathering of hams, antennas are everywhere. The largest by far was the tower at right. With a little more equipment, this antenna could do a moon bounce. It’s a shame the moon was full this weekend, and everyone went to bed early.
Giant antennas and an amateur radio trade show notwithstanding, the biggest draw is the flea market. You’re looking at about two football fields worth of parking spaces, filled with cars, tents, and collapsible tables and the strangest electronic devices you’ve ever seen. What was that like? Read on below.
If you’ve been to an apartment complex with a locked front door, you’ve seen the buzzer systems. You press the corresponding button for the apartment you want and can talk to the resident. They can press a button to unlock the door briefly, and then you go up to their apartment and they don’t have to come down to let you in. But what if you’re the resident and you want to go for a run without your keys jingling in your pocket? What if you want to open it using just your smartphone?
I knew this was a silly problem, and everyone I told about it thought that for the amount of time and effort it might save, it was hardly worth it.
How fast can I put this together using only parts I have around the apartment? Turns out about 2 hours.
[Thomas] loves his Logitech MX Master mouse, which has a pretty elaborate scroll-wheel mechanism. Perhaps too elaborate; it broke on him after a week of use, just when he was getting used to the feature. So what did he do? Took it apart and fixed it, naturally. And as a bonus, we get a guided tour of the interesting mechanism. Check out his video below to watch it in action.
The weighted scroll wheel switches between two different modes, one with a detent like you’re probably used to, and one where the wheel is allowed to spin freely for long-distance travel. And to do this, it’s actually got a little motor inside that rotates a cam and throws a lever into the side of the scroll wheel for the detent mode, and pulls the lever out of the way for free spins. It must also have some logic inside that detects how quickly the scroller is spun because it re-engages as soon as the scroll wheel stops.