ISDT – Chinese junk

I bought two ISDT Q6 Plus battery chargers over some months, and they both quickly developed the same fault symptoms:

  • jog wheel unreliable / skips; and
  • jog switch unreliable, eventually failing totally.

The worst one was disassembled. These are build a bit like mobile phones, the manufacturer did not want them being disassembled.

Here are pics of the evidence of the problem.

Above is the component side of the PCB, the right hand side is opposite to the rotary encoder for the jog wheel. The PCB around the hand soldered terminals of the encoder has a large amount of flux residue which is usually corrosive to a greater or lesser extent. Over time with atmospheric humidity, this spreads wider and wider, and in this case has penetrated both the encoder and the switch which is to the right of the PCB opening. Continue reading ISDT – Chinese junk

tinyPFA – a set of Allan Deviation plots

TinyPFA is firmware from Erik Kaashoek for NanoVNA-H4 hardware for accurate measurement of oscillator and clock source stability.

This article documents an experiment to measure the Allan Deviation of several sources:

  • Trimble Thunderbolt GPSDO;
  • Motorola R2009D service monitor; and
  • Rhode & Schwarz SML01 signal generator.

So, to make a two way comparison or three sources, there are C(3,2)=3 difference combinations, and a fourth test to document the instrument noise floor (connect the same source to both inputs).

TinyPFA and Timelab were used to make the measurements.

The GPSDO reference used was a Trimble Thunderbolt GPSDO which is locked. Continue reading tinyPFA – a set of Allan Deviation plots

tinyPFA – first experience

TinyPFA is firmware from Erik Kaashoek for NanoVNA-H4 hardware for accurate measurement of oscillator and clock source stability.

This article documents a first experience with it performing a quite simple operation, calibrating the internal 10MHz reference oscillator of two devices:

  • Motorola R2009D service monitor; and
  • Rhode & Schwarz SML01 signal generator.

The calibration reference used was a Trimble Thunderbolt GPSDO which is locked. Continue reading tinyPFA – first experience

(tr)uSDX unauthorised product and countermeasures

It has been interesting to observe takeup of the (tr)uSDX project.

The project is released under a quite restrictive licence.

Whilst the developers do not make or sell hardware, they exercise control over the hardware and offer hardware manufacturers an opportunity to have their implementation “approved” or “authorised”.

It is not surprising that a number of implementations have appeared that the IP owner regards as infringing his licence, inevitable really as Chinese copyists have little regard for intellectual property.

Who’da thought that “unauthorised” products would appear?

One of the developers posted those rigs will be banned from Firmware updates, so don’t buy that.

My correspondent asked how can he do that? Continue reading (tr)uSDX unauthorised product and countermeasures

Comparing RF Power Amplifier Tube Performance Computer and Calculate initial load line of valve RF amplifier on the AL811H

A correspondent wrote to me about Ameritron AL811H tube selection. The article contained a table of performance figures derived from RF Power Amplifier Tube Performance Computer calibrated for measured supply voltages and power output in the various modes.

Above is the table, Table 1 `from the article. Continue reading Comparing RF Power Amplifier Tube Performance Computer and Calculate initial load line of valve RF amplifier on the AL811H

Review of inexpensive Chinese thermostat – DST1000

The DST1000 targets the market for inexpensive digital thermostats, the most popular being the STC1000. The novel features to the DST1000 is that it uses  a DS1820B digital temperature sensor (well probably a Chinese clone).

The problem with thermistor based thermostats is that they commonly have significant error, and although most firmware allows the user to enter a calibration adjustment, it is a fix at one temperature and does not solve the problem that the thermistor equation implemented in the firmware does not match the behavior of the thermistor. In my experience, calibrating at 20° might result in an error as much as 5° at 80°, unacceptable for lots of wide ranging applications.

It is sold with brief and inadequate / incorrect user instructions. Two were purchased to give a good chance one would work, and you guessed it, only one worked. The lower display segment of the first digit did not work on the fautly one, and the seller thought that was not a problem. The seller frustrated attempts to obtain a refund for the faulty unit.

Above, the seller’s pic of the DST1000. Continue reading Review of inexpensive Chinese thermostat – DST1000

(tr)uSDX bootloader woes

A reader of my article WriteOptiBoot.bat asked about application to the (tr)uSDX project.

The first point to note is that the (tr)uSDX project uses its own bootloader, and it would appear it is proprietary code (ie secret), and one is entirely dependent on their published information.

A common user problem reported on the the (tr)uSDX project forum is inability to either:

  1. program the bootloader; and / or
  2. program the application code.

Continue reading (tr)uSDX bootloader woes

Garden environmental telemetry project – part 5

Garden environmental telemetry project – part 1 laid out plans for a simple maker / DIY IoT garden environmental telemetry system.

This article documents a change to the sensor configuration and payload formatter adding another temperature and humidity sensor for the greenhouse.

The sensors are now:

  • ID=1 air temperature and humidity;
  • ID=2 soil temperature and humidity.
  • ID=3 greenhouse temperature and humidity.

The payload contains an 8bit payload version number then six 16bit values for the six sensors. This is parsed by the TTN uplink formatter.

RS485-LN firmware has been upgraded to v1.4. Continue reading Garden environmental telemetry project – part 5

Another small efficient matching transformer for an EFHW – 2643251002 – #5 – improved Simsmith model (v1.03)

This article applies the improved model: An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03) to the design at Another small efficient matching transformer for an EFHW – 2643251002 – #1 – design workup.

Above is the prototype transformer wound with 14t of 0.71mm ECW tapped at 2t. The mm rule gives some scale. The turns are close wound, touching on the inner diameter of the core. Continue reading Another small efficient matching transformer for an EFHW – 2643251002 – #5 – improved Simsmith model (v1.03)