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, 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
I was intrigued by the seemingly endless stream of stories of woes with the DYS SN20A (eg RCTimer / DYS Mini SN20a / SN30a / SN40a esc), so I purchased one to see if they are all bad. Of course, impressions of a sample of size one are of somewhat limited value, but it seemed like an interesting thing to do.
Some reports of problems seem to relate to use of BLHeli on the ESCs, and it seems at least one beta release of BLHeli v14 had defects that resulted in serious damage in unprotected tests.
Discussion blames problems on front ends, flight controllers, wiring, motors, ESCs hardware, firmware, and bootloaders… but all these possible causes evident more so with this one ESC does not seem likely or logical. With the quest for more rapid FC loop response, there is a risk of instability and the drive may be working harder with oscillating demand, only logs from a flying craft will reveal what may be happening in that respect.
The test ESC
The DYS SN20A was purchased 14/06/2015 from RCTimer for about US$19 inc post. Not an inexpensive ESC by any means.
The DYS SN20A is described as an “opto” but I doubt it is optically coupled, it is probably just another instance of the fraud in terminology where opto refers to a BECless ESC. (If it were optically coupled, it would almost certainly not be a bidirectional servo interface and the SimonK bootloader would not work… but it did.)
Above, the top view of an unwrapped SN20A. Continue reading DYS SN20A out of the box
At Characterising an unknown ferrite toroid an ‘unknown’ ferrite toroid was characterised. This article uses that information for design of a Guanella 1:1 current balun.
The proposed design uses 11t of small coax wound in the Reisert ‘cross-over’ style.
The impedance of a single turn vs freq was used to predict the impedance of an 11t choke. Such a choke exhibits a self resonance that can be represented as due to an equivalent shunt capacitance. This equivalent capacitance is not easily estimated, and can best be determined by calibrating an analytical model of the choke for the same self resonance as exhibited by a real choke.
Above is common mode impedance from an analytical model of the choke, assuming an equivalent self capacitance of 11pF.
Continue reading Designing a Guanella 1:1 balun using the ‘unknown’ ferrite toroid
The ‘unknown’ toroid is wound with a single turn and measured with a VNA, an AIMuhf in this case.
Of interest in the first instance is the apparent inductance of the single turn winding at low frequencies where typically permeability µ is fairly constant and core loss is fairly low. Continue reading Characterising an unknown ferrite toroid
There seems a never ending stream of low end antenna analysers appearing.
The Mini60 antenna analyser is one in that vein, and is sure to prove popular because of its low price. As is common, there does not appear to be an English language user manual and the specifications in eBay ads are not very reliable (eg weight: 200kg).
Above is a screenshot from an online demo of the Mini60 on a 7MHz antenna. Continue reading Mini60 antenna analyser
I bought a USBTiny AVR programmer on eBay for about A$8 posted.
Above, the seller’s pic of the package.
It is almost always the case that the ISP headers on the programmer use the standard pinout published by Atmel, and in that case the supplied ISP cables need to be pinned pin for pin, ie pin 1 to pin 1 etc.
If you look carefully at the pic, the key is towards the top of the pic which means pin 1 on the right hand plug is towards the viewer and pin 1 on the left hand plug is away from the viewer. The cable does not connect pin 1 to pin 1, and as a consequence the package did not work.
There is more than one way to connect these plugs, and above is one way that does connect pin 1 to pin 1, and the cable and USBTiny work. Though the seller has been told of this defect, he continues to sell the item with the pic of the defective cable.
One wonders how many thousands of these things are and will be sold with this defect.
There are a number of USB-RS232 adapters available, among them Silabs, FTDI, Prolific and WCH.
The Silabs CP series adapters have been reliable but not very widely used.
The Prolific adapters are, well, prolific… but given their major compatibility problems and poisoned drivers, they are not a good choice.
FTDI was a good choice until they distributed through Microsoft Windows Update their device poisoning trick to disable chips they thought counterfeit… though they seemed to have backed away from that action.
The new kid on the block is an adapter by Chinese company WCH, chips that appearing in lots of low cost devices, eg Arduino Nano clones with WCH adapters instead of FTDI selling for around A$3+ on eBay whereas the FTDI equipped Nanos are more like A$12.
This article compares the WCH CH340G and FTDI FT232RL.
Above are two inexpensive adapters for Arduino boards, the upper one is FTDI based at A$8 each (inc post), and the lower one WCH based at 3 for $3.60 (inc post). Continue reading A tale of two USB-RS232 adapters