App note: Driving electronic paper displays (E-paper)

Silicon Labs’ app note on driving E-paper with their EFM32 micro. Link here (PDF)

Electronic Paper Displays (EPDs) are types of displays that are reflective and bistable. Reflective in this case means that they rely solely on ambient light and does not use a backlight. Bistable is the property of retaining an image even when no power is connected.
EPDs are commonly used in e-readers, industrial signage and electronic shelf labels. Their properties are ideal for applications which do not update the image frequently. Since the display draws no current when showing a static image, they allow for a very long battery lifetime.

App note: Designing with an inverted-F 2.4 GHz PCB antenna

PCB design guide for an inverted-F 2.4 GHz antenna from Silicon Labs. Link here (PDF)

One of the main reasons to use a PCB antenna is to reduce cost. Since the antennas are printed directly on the board, they are generally considered to be free. On boards with room to spare, this will be true. On boards that need to grow to account for the increased size of the printed antenna, you must include the added cost of the larger PCB when calculating cost savings.

App note: Secure hash algorithms back to basics

Maxim Integrated’s introduction to SHA security. Link here (PDF)

This application note goes over the basics of Secure Hash Algorithms (SHA) and discusses the variants of the algorithm. It then briefly touches on how the algorithm is used for authentication, including the concept of a Hashed Message Authentication Code (HMAC). It concludes by looking at some of the Maxim secure authenticators that can be used to very easily deploy SHA algorithms for security applications.

App note: Optocouplers in on-board chargers and battery monitoring systems

App note from Vishay on how optocouplers play a role on safety for Electric vehicles. Link here (PDF)

The number of electric vehicles on the roads is steadily growing, increasing the need for safe and reliable battery systems and high efficiency battery chargers. Modern electric vehicles use battery systems with voltages up to 1000 V and charge times down to a few hours. This application note uses two examples to illustrate how optocouplers play a major role in on-board chargers battery monitoring systems, and explores the benefits they provide to designers and drivers.

Reverse-engineering the classic MK4116 16-kilobit DRAM chip

Ken has written an article on reverse-engineering the classic MK4116 16-kilobit DRAM chip:

Back in the late 1970s, the most popular memory chip was Mostek’s MK4116, holding a whopping (for the time) 16 kilobits. It provided storage for computers such as the Apple II, TRS-80, ZX Spectrum, Commodore PET, IBM PC, and Xerox Alto as well as video games such as Defender and Missile Command. To see how the chip is implemented I opened one up and reverse-engineered it. I expected the circuitry to be similar to other chips of the era, using standard NMOS gates, but it was much more complex than I expected, built from low-power dynamic logic.

See the full post on Ken Shirriff’s blog.

FV-1 based mini SDR radio

FV-1 based mini SDR radio @

I have really enjoyed my FV-1 based mini SDR radio but it has one problem…its too small! I made the thing so small; it’s hard to operate and assemble. So I decided to make it a little larger, allowing for all the controls to be larger and more spaced out. It has a larger display and the circuit board layout provides for the switches, encoder, volume control and display all to be soldered directly to the board. All of the circuit components are now on the top side of the board as well. Along with these physical changes, I made some minor circuit changes.

Check out the video after the break.

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App note: Control solution using logic, analog switches, and discrete semiconductor devices for reversing a one-phase motor

App note from Littelfuse on solution to control split-phase motor using logic devices and triacs. Link here (PDF)

In the huge variety of the AC motors, one-phase motors are an excellent option when only the single-phase power is available to supply electrical energy which motors require to operate. One of the most common single-phase motors is the split-phase motor which is used in many applications, such as pumps, bench drills, compressors, vacuum cleaners, electrical sewing machines, etc.
In some if these applications it is necessary to reverse the motor which requires two conditions. The first condition is the removal of power to the motor in order to stop it. The second condition is to change the electrical connections between the mainand the start winding.

App note: Circuit protection solution for lithium cells

App note from Littelfuse on PolySwitch PPTC for lithium cells protection. Link here (PDF)

Primary lithium cells (i.e., AA and 2/3A) and rechargeable lithium cells (i.e., 18650, 17500, and prismatic) are used in many portable electronics applications, such as laptop or notebook computers. Their popularity is based on the fact that they offer high energy density, high capacity and long cycle life, with no memory effect.
Lithium cells are sensitive to faults caused by overcurrent and overtemperature conditions that may result from accidental shorting of the cell terminals and, in the case of rechargeable lithium cells, abusive charging or charger failure. For this reason, lithium cells generally require individual protection.

Reverse-engineering the carry-lookahead circuit in the Intel 8008 processor

Reverse-engineering the carry-lookahead circuit in the Intel 8008 processor:

The 8008 was Intel’s first 8-bit microprocessor, introduced in 1972. While primitive by today’s standards, the 8008 is historically important because it essentially started the microprocessor revolution and is the ancestor of the modern x86 processor family. I’ve been studying the 8008’s silicon die under the microscope and reverse-engineering its circuitry.

More details on Ken Shirriff’s blog.

App note: How to determine if an eFuse system can be safely hot−plugged

This app note from ON Semiconductors linked here (PDF)

System designers must account for voltage surges that occur when supplies or loads are connected. eFuses are integrated circuits with many features to protect loads from these surges. However, it is important to ensure that the eFuse itself will not receive excessive voltage on its input.
This application note uses mathematical calculations, simulations, and actual lab data to illustrate the voltage surge as an eFuse is suddenly connected on the input side. System designers can use this information to make certain that the eFuse will be within its limits.

App note: Analysis of power dissipation and thermal considerations for high voltage gate drivers

App note from ON Semiconductors on ways to dissipate thermals or reduce junction temperature of HVIC. Link here (PDF)

Gate drivers used to switch MOSFETs and IGBTs at high frequencies can dissipate significant amount of power depending on the operating conditions. It is important to determine the driver power dissipation and the resulting junction temperature in the application to ensure that the part is operating within acceptable temperature limits.

Low-cost open source ventilator-ish device

Johnny made a low-cost ventilator-ish device, that is available on GitHub:

In the event that COVID-19 hospitalizations exhaust the availability of FDA approved ventilators. This project documents the process of converting a low-cost CPAP (Continuous Positive Airway Pressure) blower into a rudimentary non-invasive pressure support ventilator that could help with breathing during respiratory distress. It’s an evolving project, but in it’s current form, it most aligned with the definition of a non-invasive pressure support BiPAP ventilator.
This same project can also be used to create a reasonable low-cost Powered Air Purifying Respirator (PAPR) with filter adapter and mask.

See the full post on Johnny Chung Lee’s project blog.

Check out the video after the break.

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App note: Termination recommendations for single-ended oscillator driving single or multiple Loads

Proper clock signal terminations app note from SiTime. Link here (PDF)

Clock signals with fast edges see traces on Printed Circuit Boards (PCB) as transmission lines rather than simple wire connections. If the length of PCB trace exceeds certain limit it requires matching of the trace impedance to one or both of the source and load impedances. Impedance mismatch causes signal reflections travelling back and forth the transmission line causing signal distortions such as ringing, overshoots, and undershoots.

App note: Interfacing an STM32L1xx microcontroller with an external I2S audio codec to play audio files

I2S protocol interfacing with an STM32 microcontroller app note from ST Microelectronics. Link here (PDF)

The I2S protocol is widely used to transfer audio data from a microcontroller/DSP to an audio codec in order to play melodies (stored in a memory) or, to capture analog sound (from a microphone).
The STM32L1xx allows I2S audio communication using the SPI peripheral, and implements specific functionalities for this communications mode.

App note: Is the lowest forward voltage drop of real schottky diodes always the best choice?

App note from IXYS about the pros and cons of different forward voltage drop of real shottky diodes. Link here (PDF)

According to the thermionic emission model, pure Schottky barriers exhibit a forward voltage drop, which decreases linearly as the barrier height diminishes; whereas the reverse current increases exponentially as the barrier height decreases. Consequently, there exists an optimum barrier height, which can minimize the sum of forward and reverse power dissipation for a particular application.
However, discussions with the users of Schottky diodes reveal that they do not search for the minimum of forward and reverse power dissipation but always for the minimum forward voltage drop. Values of reverse current are very rarely asked for. One must know how the Schottky diode is being applied in order to objectively select the most appropriate part.

App note: Voltage vs. output speed vs. torque on DC motors

App note from Precision Microdrives about DC motor capabilities and their uses. Link here

Why Change Torque?
The most obvious benefit of varying the torque is to maintain a constant speed when the motor’s load varies, keeping in mind the interdependent nature of speed, torque, and voltage.

Although this example may be outdated, audio cassettes are a great way of explaining how some applications need to vary the torque to match a changing load. As the cassette plays and the audio tape moves from one spindle to the other, the driving motor will experience a change in load. However, the playback must remain at a constant speed throughout – otherwise the audio pitch would be affected.

Why Change Speed?
The ability to vary motor speed whilst maintaining a steady torque is essential to many applications for a variety of reasons.

An example of an application that requires a variable speed and steady torque is an audio CD player as it is commonly observed that the CD will rotate faster at certain points than others. This is because the information is stored in spiralled circular tracks on the disk and the length/circumference of the track is directly proportional to the amount of information stored on them. This means that the speed must be decreased as the laser is reading from the outermost tracks because there is more information per revolution. Inversely, the speed is increased as the laser reads from the innermost tracks as the spiral circumferences are smaller and therefore contain less information per revolution.

ClockSquared Mini

Willem has been working on a tiny word clock, the Clocksquared Mini:

Summer break is here, and with some time to spare I decided to challenge myself with a project that I call “Clocksquared Mini”. It is Clocksquared, but in a tiny wristwatch package. This gives rise to a major challenge, as everything has to be shrunk down approximately ten times from a 300x300x50 mm to an approximately 35x35x7 mm package. Moreover, running everything off a tiny battery whilst maintaining an acceptable battery life also turns out to be quite difficult.

Project info at

Designing a Memory/IO (ETA-3400) addon for the ET-3400 trainer

Dr. Scott Baker designed and built an ETA-3400 Memory/IO accessory for the vintage Heathkit ET-3400 trainer, that is available on GitHub:

I’ve always wanted one of these Heathkit microprocessor trainers, and finally one caught my eye on eBay and I pulled the trigger. The basic interaction with the trainer is through the onboard keypad and LED displays, but Heathkit also made an accessory that added additional ROM, RAM, serial port, and a cassette interface.
This allowed you to use a machine monitor over the serial port, and even featured a Tiny Basic interpreter in ROM that allowed the trainer to be programmed in Basic.

See the full post at

Check out the video after the break.

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App note: TQFN package thermal pad via design guide

TQFN footprint pad via design guide for proper thermals from Diodes Incorporated. Link here (PDF)

TQFN packages have exposed pads to provide excellent electrical grounding paths to the PCB and transfer the device heat through thermal vias on the PCB thermal landing to the internal copper planes. In order to maximize the removal of heat from the package, the number of vias, the size of the vias, and the construction of the vias must be considered for the thermal landing pattern. The exposed pad must be soldered down to ensure adequate heat conduction from the package.