In a few weeks the Hackaday community offline password keeper will reach a crowdfunding platform. This is a necessary step as only a high production volume will allow our $80 early bird perk target. We’ll therefore need you to spread the word.
Thanks to the Chromium development team, a few days ago the Mooltipass installation process became as simple as installing our app & extension. As you may remember, our device is enumerated as composite HID proprietary / HID standard keyboard. This makes it completely driverless for all operating systems and enables standalone operation as the Mooltipass can type logins and passwords selected through its user interface. Management communications are therefore done through the Mooltipass HID proprietary interface, which Chrome 38 now natively supports through its chrome.hid API. The simpler our installation process is, the more likely the final users will appreciate the fruit of our hard labor.
A few months ago Hackaday covered the xNT crowdfunding campaign which aimed at making an NTAG216 based NFC implant for different purposes. I actually backed it, found that standard NFC readers don’t perform well and therefore decided to try using a standard coil as an antenna for better reading performances.
Most NFC readers typically only have a small sweet spot where implant reading is possible. This is due to what we call coupling factor which depends on the reading distance and reader & NFC tag antenna geometries. Having a smaller antenna diameter increases the coupling factor and makes implant positioning easier.
In my detailed write-up you’ll find a good introduction to impedance matching, a process where a few passive components are added in series/parallel with an antenna to bring its complex impedance close to a RF signal transmitter’s. This usually requires expensive tools but allows optimal power transmission at a given frequency.
You may find our xNT coverage here.
The development of the Hackaday community offline password keeper has been going on for a little less than a year now. Since July our beta testers have been hard at work giving us constant suggestions about features they’d like to see implemented and improvements the development team could make. This led up to more than 1100 GitHub commits and ten thousand lines of code. As you can guess, our little 8bit microcontroller’s flash memory was starting to get filled pretty quickly.
One of our contributors, [Miguel], recently discovered one compilation and one linker flags that made us save around 3KB of Flash storage on our 26KB firmware with little added processing overhead. Hold on to your hats, this write-up is going to get technical…
Many coders from all around the globe work at the same time on the Mooltipass firmware. Depending on the functionality they want to implement, a dedicated folder is assigned for them to work in. Logically, the code they produce is split into many C functions depending on the required task. This adds up to many function calls that the GCC compiler usually makes using the CALL assembler instruction.
This particular 8-bit instruction uses a 22-bit long value containing the absolute address of the function to call. Hence, a total of 4 flash bytes are used per function call (without argument passing). However, the AVR instruction set also contains another way to call functions by using relative addressing. This instruction is RCALL and uses an 11-bit long value containing the offset between the current program counter and the function to call. This reduces a function call to 2 bytes and takes one less clock cycle. The -mrelax flag therefore made us save 1KB by having the linker switch CALL with RCALL instructions whenever possible.
Finally, the -mcall-prologues compiler flag freed 2KB of Flash storage. It creates master prologue/epilogue routines that are called at the start and end of program routines. To put things simply, it prepares the AVR stack and registers in a same manner before any function is executed. This will therefore waste a little execution time while saving a lot of code space.
More space saving techniques can be found by clicking this link. Want to stay tuned of the Mooltipass launch date? Subscribe to our official Google Group!
[Kalle] tipped us about a quick project he made over a couple of evenings: an inductor saturation current tester. All the components used for it were salvaged from a beefy telecom power supply, which allows the tester to run currents up to 100A during 30us in the inductors to be characterized.
Knowing the limits of an inductor is very convenient when designing Switch Mode Power Supplies (SMPS) as an inadequate choice may result in very poor performances under high loads. [Kalle]’s tester simply consists in a N-Mosfet switching power through a load while a shunt allows current measurements. The saturation point is then found when the current going through the inductor suddenly peaks. As you can see from the picture above, 16 4700uF electrolytic caps are used to compensate for the sudden voltage drop when the Mosfet is activated. A video of the system in action is embedded after the break.
Continue reading “Making an Inductor Saturation Current Tester”
[Eswar] is not an ordinary 16 years old boy. He figured out a noninvasive way to measure breathing in hospitals for less than $50. He is using a theremin to measure the rise and fall of a patient’s chest. For our curious readers, this touch-less instrument was invented back in 1929 by the Russian inventor [Leon Theremin]. It uses the heterodyne principle and two oscillators to generate an audio signal. One electronic oscillator creates an inaudible high pitch tone while another variable oscillator is changed by adding capacitance to an antenna.
As you can guess the space between the patient’s chest and the antennas placed around the bed forms a tiny capacitor which varies when exhaling. With three simple TTL chips and a little guessing [Eswar] had a working prototype ready to be implemented in the real world. If you’re interested in theremin, we invite you to see one of our previous articles on how to make one in a few minutes with a soda can.
Some of our dear readers may already have an infallible system to remember different complex passwords for the different websites they visit daily. This is why they may have not been following the offline password keeper that the Hackaday community is building.
The Mooltipass has a characteristic that may regain their interest: it is possible to connect Arduino shields to it. In the video embedded below you can see the Arduino conversion process our development team imagined a few months back. The operation simply consists in using a knife to remove plastic bits on top of standard Arduino headers. We also embedded a few use cases with their respective sketches that may be downloaded from our official GitHub repository.
As with stacking several shields, a little tweaking may be required to keep the functionalities from both the Mooltipass and the connected shield. We therefore strongly welcome Arduino enthusiasts to let us know what they think of our setup.
In the meantime, you may want to subscribe to our official Google Group to stay informed of the Mooltipass launch date.
Continue reading “Developed on Hackaday: Mooltipass Arduino Shields Compatibility”
We’re quite sure that all hobbyists have used the 7805 voltage regulator at least once in their lives. They are a simple way to regulate 7V+ voltages to the 5V that some of our low power projects need. [Ken Shirriff] wrote an amazingly detailed article about its theory of operation and implementation in the silicon world.
As you may see in the picture above such a regulator is composed of very different elements: transistors, resistors, capacitors and diodes, all of them integrated in the die. [Ken] provides the necessary clues for us to recognize them and then explains how the 7805 can have a stable output even when its temperature changes. This is done by using a bandgap reference in which the difference between transistor base-emitter voltages for high and low current is used to counter the effects of temperature. As some elements looked a bit odd during [Ken]’s reverse engineering process, he finally concluded that what he purchased on Ebay may be a counterfeit (read this Reddit comment for another opinion).