Frank Adams details this interesting project on Hackster:

Laptop Battery Charge Controller

his project is for those that want to turn an old laptop into a portable Raspberry Pi. My previous Hackster.io projects showed how to connect the keyboard and touchpad. The LCD is easy to convert to HDMI with a video card from EBay. The missing piece has been a way to charge the original lithium battery pack. To solve this problem, I designed a circuit board in Eagle that uses a Max1873 charge controller with an ATtiny85 as a supervisor. The board shown below was fabricated by OSH Park. The Eagle board and schematic files plus the ATtiny code can be downloaded below.

The Max1873 has been around a long time and needs a microcontroller to handle the tasks that a newer charger IC would have, built in. I have prior experience with this chip and found it to be fairly simple and easy to get working. The schematic below shows how the ATtiny85 is powered from the 5.4 volt regulator in the Max1873. This means the ATtiny is only operating if the wall supply is plugged in. The ATtiny outputs a logic signal that turns on an NFET which in turn disables the Max1873. This 5.4 volt logic signal is attenuated to a 3.3 volt level so it can be monitored by the Pi. If the ATtiny is not installed in it’s socket, the Max1873 will be enabled. The Pi could drive the “Charger_TP” signal to disable the charger if the battery values read over the SMBus show it’s necessary.

Now that it is relatively cheap and easy to create a PCB, it is a common occurrence for them to be used in projects. However, there are a lot of subtleties to creating high-performance boards that don’t show up so much on your 555 LED blinker. [Robert Feranec] is well-versed in board layout and he recently highlighted an animation on signal crosstalk with [Eric Bogatin] from Teledyne LeCroy. If you want a good understanding of crosstalk and how to combat it, you’ll want to see [Eric’s] presentation in the video below.

Simplifying matters, the heart of the problem lies in running traces close together so that the magnetic fields from one intersect the other. The math is hairy, but [Eric] talks about simple ways to model the system which may not be exact, but will be close enough for practical designs.

The models use inductors and capacitance to represent different modes of crosstalk, and it’s likely you already know how to deal with those quantities. The video shows some simulations and also suggests methods to control the problem.

Even though the topic is PC boards, some of the same ideas apply to cables. Ethernet cables, for example, have specifications for FEXT for similar reasons.

Read more on Hackaday…

Awesome project from the Technoblogy blog:

Frequency Probe

The Frequency Probe is a handheld tool designed to help you debug your circuits by giving a visual indication of the frequency or voltage at the probe. For a periodic waveform it gives a digital readout of the frequency, with a range of about 1Hz to 5MHz and an accuracy of better than 0.3%. For a voltage level it gives a readout of the voltage:

The obvious way to implement a frequency meter is to count the number of pulses within one second; this then directly gives the frequency. I refer to this as Frequency Mode. The disadvantage of this method is that a long sample time is needed to measure low frequencies accurately.

The other way is to measure the interval between two pulses of the input signal; the reciprocal of this then gives the frequency. I call this Interval Mode. For example, if the interval between pulses is one second the frequency is 1Hz. The disadvantage of this method is that for high frequencies you need to measure the interval very accurately.

The ideal solution is to use Frequency Mode for high frequencies, and Interval Mode for low frequencies, which is the approach I’ve adopted with the Frequency Probe. I explain below how to calculate the best point at which to switch between modes.

I originally started work on this project a couple of years ago, but it turned out to be a lot trickier than I anticipated, and so decided to put it to one side. I revisited it earlier this year, and fortunately managed to solve all the issues.

Cabe Atwell writes on Hackster about Open Authenticator by Vedant Parajape which uses an ESP32 to secure data and features an OLED display, 300mAh LiPo battery, and a USB Type-C port for charging:

TOTP-Based Open Hardware Authenticator Powered by an ESP32 Microcontroller_

“I fired up google and tried to search about it, and surprisingly it used a pretty amazing concept. It had a shared key with the server, and then it did some computation on the shared key and current UTC time to get a 6-digit number. So, the remote device just had to be accurate at timekeeping,” Parajape noted in his project log. He then took that information and designed his initial Open Authenticator prototype using a development kit he had on hand and an ESP32 module. It worked well enough, but he wanted a more streamlined platform, similar to RSA’s SecureID Key FOB.

Some people like to use hardware authenticators or security keys when working with public or company computers to keep their data private, certainly so when hackers can easily steal unprotected information. There are many great authenticators on the market that can be had for cheap, but others such as developer Vedant Parajape have designed their own platforms using readily-available hardware. Parajape became interested in authenticators after seeing his dad’s security keys and wondered how they could generate code without being connected to a network.

.@ve0x10's Open Authenticator is an open source, TOTP-based hardware authenticator powered by an ESP32: https://t.co/wHuKIRA8ZR pic.twitter.com/rJTxLR5lxy

— Hackster.io (@Hacksterio) January 26, 2021