I have been intrigued by the huge number of sellers of very low cost 18650 Li-ion cells on eBay.
Could they be any good?
As a reality check, Panasonic cells around 3000mAh sell through traditional channels here in Australia for around A$20 per cell, there are Australian eBay sellers selling cells advertised as Panasonic for around A$22 per pair posted.
Above, the GTL red LS18650 5300mAh Li-ion cell purchased in a lot of five for $1.30 each (inc post from China). The rated capacity is more than 50% higher than the maximum from brand name products. Continue reading 18650 Lithium Ion cells on eBay
I have recently installed the Threshold 2 update to Win 10, and apart from a number of small issues, it seriously broke my grabber environment on a 64 bit machine.
The error messages:
5 [main] lftp 2944 C:\bin\lftp\bin\lftp.exe: *** fatal error in forked process - fork: can't reserve memory for parent stack 0x600000 - 0x800000, (child has 0x400000 - 0x600000), Win32 error 487
1481 [main] lftp 2944 cygwin_exception::open_stackdumpfile: Dumping stack trace to lftp.exe.stackdump
6 [main] lftp 5008 fork: child -1 - forked process 2944 died unexpectedly, retry 0, exit code 0x100, errno 11
For that environment, I use an lftp port to Windows (https://nwgat.ninja/lftp-for-windows/), and had installed the 64bit verion which is essentially a cygwin compilation packaged with the necessary DLLs. (This issue probably more widely affects cygwin, or perhaps just the bash shell under cygwin.) Continue reading Win 10 Threshold 2 issues
I have successfully implemented a few projects on the STC 15F104E, a Chinese 8051 architecture MCU.
The chip includes EEPROM, and some flexible extensions to the timers which potentially make it more useful than a standard 8051.
I have previously observed that the documentation is poor, and the programming tool is poor.
The project that led to the latest observations was an attempt to implement RC PWM – ON/OFF switch originally on one of these chips as it contained sufficient resources to suit the application. One of those resources was an +/- edge triggered INT0.
The code worked fine, but for only a short and variable period. Essentially, the the main loop was executing fine, the chip stopped triggering the interrupt service routing for INT0 after a variable time from 10s to 1000s… but it ALWAYS stopped working. Cycle the power and the same thing is observed. Continue reading Revised thinking on STC chips
This article describes a remote ON/OFF switch which uses an RC receiver and adapter chip to convert the RC PWM signal into an ON/OFF output. (Suitable RC transmitters are on hand.)
The immediate application is for remote ON/OFF PTT or KEY of a transmitter for field strength testing at various locations.
Remote control hobbies have long used a multi channel digital proportional protocol for control of planes etc. The simplest multi channel receiver has an independent PWM output for each servo.
The PWM signal is a 1000-2000µs pulse with a repetition rate from about 50Hz up to 500Hz or so, the duration of the pulse conveys the information.
The converter chip is a ATTiny25 MCU with firmware that monitors the PWM stream and provides ON/OFF and OFF/ON output pins. For the immediate application, the ON/OFF (or non inverted) output drives a 2N7000 FET with ‘open collector’ output suited to the PTT and KEY lines of most modern transceivers.
The firmware ignores PWM signals with duration outside the range 900µs to 2100µs, and switches ON at 1600µs, and OFF at 1400µs to provide some hysteresis. If PWM input is lost for 125ms, the output will fail safe OFF.
Above is the schematic. The 2N7000 is good for 60V, can handle up to 100mA without a heat sink, and had a body diode to absorb transients if the load is a relay. Continue reading RC PWM – ON/OFF switch
An upcoming project calls for a stand alone GPS logger.
The requirement is for a GPS stream that allows correction using RTKLIB, but this trial is of a lesser GPS as proof of concept.
Above, the equipment consists here of a Ublox NEO-6M based GPS module (~A$15 incl on eBay) at left, an Openlogger (~A$15 incl post on eBay) at right, and a 12V-5V converter (~A$7 from Hobbyking) at bottom. The latter is a 5A converter, way overkill, but it was on hand. The GPS module has a 3V regulator on board for the NEO-6M chip.
Continue reading Trial of prototype stand alone GPS logger
A drive test of the OpenLog logger collecting raw NMEA data in parallel with the TinyTrak (VHF) was conducted. To maximise the performance of APRS, a fill-in digi / iGate was run at my home. The tracker used a 65W transmitter with quarter wave vertical in the centre of the car roof.
Above is an overview of the APRS and OpenLog tracks. Click on the image for a scaleable / zoomable view in Google Maps. Continue reading OpenLog for TinyTrak – drive test
There are a host of factors that contribute to data loss in APRS, to name just some:
- non-standard / sub-standard / poorly configured digipeaters;
- defect ridden iGates that lose, duplicate and corrupt packets;
- poorly configured mobiles;
- network congestion and interference;
- unpredictable equipment failures;
- basic geographical coverage of the network; and
- dependence on the ionosphere for HF APRS.
This article describes an enhancement to the popular TinyTrak (and its clones) to also capture the GPS stream to an inexpensive local data logger.
The logger does not interfere with normal radio APRS, it coexists with it and creates a properly timestamped fine detail log of positions over a very long time, a log that can be post processed into a range of graphic / map and tabular reports.
The datalogger used in an OpenLog. It is a simple logger that writes data to a micro SD card formatted FAT16/32 up to 32GB, costs about $A12 (inc post) for the logger and about A$10 (inc post) for a 16GB Class 10 micro SD card. (A slower card could be used, but they aren’t much cheaper.)
Above, the OpenLog data logger.
Continue reading OpenLog for TinyTrak
This article describes an enhancement to the DIY USB password generator, a small USB HID keyboard device that types a password stored in EEPROM automatically when it is attached.
The implementation was on a Digispark ATTINY85 General Micro USB Development Board which was purchased on eBay for a few dollars. The board uses different pin connections to USB to the original. Continue reading DIY USB password generator – (USB PRC) enhanced #1
This article describes an implementation of the DIY USB password generator. It is a small USB HID keyboard device that types a password stored in EEPROM every time it’s attached.
The implementation was on a Digispark ATTINY85 General Micro USB Development Board which was purchased on eBay for a few dollars.
The board uses different pin connections to USB to the original, and requires a hardware jumper from D+ (PB4) to INT0 (PB2).
In the process of changing the code, I updated the V-USB driver. That necessitated quite a few changes to source code.
The updated code was compiled, and tested just fine.
Changed / updated code (includes hex): usb_tiny85_passgen.zip.
In designing a Guanella 1:1 balun, selecting a ferrite core that has been characterised by the manufacturer simplifies the design process greatly.
The manufacturer’s full characterisation includes curves for complex permeability vs frequency and from these the magnetising impedance of the core can be calculated. Note though that tolerances on magnetics are usually fairly wide and they can be quite temperature dependent.
The inductor will usually exhibit a self resonance that is not revealed by the above calculation, but can be reasonably well modelled by adding a small equivalent shunt capacitance, see (Knight 2008). This equivalent capacitance is usually very important and not so easy to estimate, and is often best estimated by careful measurement of the self resonant frequency of the inductor (taking care to back out fixture effects). With experience, one can make a fairly good first guess so that the process is not too iterative.
Some writers say that Cs increases as turns are increased, but (Knight 2008) shows quite the opposite.
Controlling inductor self resonance is a lot about controlling added stray capacitance, eg connecting wires, encapsulation in conductive boxes etc.
Above is a plot of common mode impedance of a FT240-43 ferrite toroid with 11t wound in Reisert cross over style and Cs=3pF. Different scenarios will give different results, but the form will tend to be similar to above. Continue reading Some tools for designing a Guanella 1:1 balun using ferrite toroids