What is the impact of oscilloscope bandwidth on the observed signals? Does a bandwidth of 25 MHz mean that a scope will display a 30 MHz signal only with a lower amplitude? Can oscilloscopes work around Nyquist with equivalent sampling? Is a scope four times the bandwidth worth four times the price? Let’s have a look! (spoiler: it is complicated)
Beware of JDY-30 Bluetooth SPP modules
Bluetooth to serial modules have been around almost forever. Just connect power, ground, RXD, TXD, maybe a config pin and you have a trivial way to transmit data wirelessly from an embedded system to a PC or Android device.
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Disk space monitoring & e-mail notifications with Bash
Running out of disk space is a common problem for unattended Linux boxes like database servers or backup storage servers. Usually I would use Zabbix (or Nagios) do to the monitoring, but it would be an overkill for a Raspberry Pi or a single NAS, so I made a small Bash script. This script runs df, checks disk usage and sends mail in case the free space is running low.
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Waveshare ePaper display library
I bought a pair of ePaper displays from Waveshare with the intent to use them in a wireless sensor network for displaying slowly changing data. The reference code from Waveshare is quite clunky and not so easy to re-use, so I made my own small, portable graphics library and display driver (with ARM Cortex-M in mind).
The library is available on Github.
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Making graphics and fonts for embedded systems
Microcontroller systems with graphical displays require a way to display text. In case of alphanumeric displays (like HD44780) it is easy – just send your ASCII bytes to the display. Graphical displays operate on individual pixels, so firmware must generate the graphics and texts on the fly.
In this post I show the complete multi-step process from a TrueType (.ttf) font file to autogenerated C code that can be used by a graphics library to display texts on a microcontroller. All code (including the embedded graphics library) is available on Github.
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The Youkits TJ5A is now my primary transceiver. I bought it with portable operation in mind (I do not have much space for decent antennas at home). Read more for high-resolution photos.
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Small, cheap power supply modules from Aliexpress
I have recently bought a BananaPi with the intent of making a automotive datalogger. I needed a simple power supply that would work reliably in my car. I found some nice looking modules in “The Thick Electronic” store on Aliexpress.
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B6AC battery charger teardown
I recently got some discarded NiCd batteries from emergency lighting fixtures (5 cells, 7 Ah) and I started looking for a way to check if they might still work. While searching for chargers I found model B6AC that: charges automatically almost any battery chemistry (various lithium, NiCd, NiMH, lead-acid), can discharge batteries in a controlled way, balance li-ion battery cells, can cycle the battery through several charges and discharges, indicates the charge and discharge capacity (and probably some more features I still do not realize).
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