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

Last update: 10th December, 2022, 3:44 PM

(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

Last update: 13th December, 2022, 8:40 AM

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

Last update: 20th December, 2022, 7:15 AM

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)

Last update: 29th January, 2023, 7:38 PM

A Simsmith model of a Ruthroff 1:4 voltage balun – 2843009902 (BN43-7051)

A correspondent asked whether I had a tool similar to An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03) to assist in the design of a ferrite cored Ruthroff 1:4 balun for HF.

In fact, the problem is the same as the one discussed in the article above, and the model is suited to application to the ferrite cored HF Ruthroff 1:4 balun case.

This analysis applies to a Fair-rite 2843009902 but may not apply to other manufacturer’s BN43-7051.

Above is a screenshot of the model calibrated against measurement. The magenta curve is the prediction and the blue curve is the measurement. Note that very small differences in measured value result in apparently large changes in InsertionVSWR, these two curves reconcile very well, especially considering the tolerances of ferrite material. Continue reading A Simsmith model of a Ruthroff 1:4 voltage balun – 2843009902 (BN43-7051)

Last update: 24th November, 2022, 3:32 PM

Another small efficient matching transformer for an EFHW – 2 x 5943000601 (FT82-43) – VK4JJ build and measurement

The transformer is an autotransformer of 3+21 turns single layer close wound on a ‘stack’ of two Fair-rite 5943000601 cores (FT82-43?). Note that these were genuine Fair-rite stock, other #43 mix products in the market place may be significantly different (see Ferrite cored RF chokes in Class-E RF power amplifiers – core material issues for more discussion).

There are a plethora of designs using FT82-43 published on the ‘net, most of them have appalling loss.

Above is a Simsmith model and measurement of the transformer for reconciliation. The blue VSWR curve is the measurement and the magenta curve is the calibrated model, they agree well considering the tolerance of ferrite materials. Continue reading Another small efficient matching transformer for an EFHW – 2 x 5943000601 (FT82-43) – VK4JJ build and measurement

Last update: 17th November, 2022, 10:37 AM

Another small efficient matching transformer for an EFHW – LO1238 – VK3PY, VK3TU build and measurement

This article documents the process of design, prototyping, measurement and final build of a 1:49 impedance ratio (1:7 turns ratio) EFHW transformer, exploring some alternative designs along the way, a collaboration between VK3PY and VK3TU with a little guidance.

The transformer is wound on a Jaycar LO1238 35x21x13mm toroid of L15 material (L15 appears to be a NiZn ferrite based on its very high resistivity), they sell at $7 for a pack of two.

2:14 winding

The first test was of a 2:14 turn winding terminated in a 2450Ω load. The transformer is an autotransformer of 2+12t with 91pF compensation capacitor installed in shunt with the 2t winding.

As expected, |s11| is pretty poor at the low end, corresponding to an InsertionVSWR=1.7 @ 3.5MHz.

Design rejected due to high InsertionLoss, magnetising admittance too high.

3:21 turn windings

The transformer is an autotransformer of 3+18t with 91pF compensation capacitor installed in shunt with the 3t winding. Continue reading Another small efficient matching transformer for an EFHW – LO1238 – VK3PY, VK3TU build and measurement

Last update: 16th November, 2022, 10:17 AM

An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03)

The article A simple Simsmith model for exploration of a common EFHW transformer design – 2t:14t proposed a simple model.

The previous proposal

Above is the equivalent circuit used to model the transformer. The transformer is replaced with an ideal 1:n transformer, and all secondary side values are referred to the primary side.

The model works quite well for low leakage inductance / low ratio transformers but falls down for the higher leakage inductance / higher ratio transformers.

An improved model

The improved model is similar, but Cse in the model above is distributed to the outer sides of the lumped constant model.

Above is the equivalent circuit used to model the transformer. The transformer is replaced with an ideal 1:n transformer, and all secondary side values are referred to the primary side. Continue reading An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03)

Last update: 1st June, 2023, 3:46 AM

Modelling an antenna as a simple two terminal resistance is often naive

in the article A simple transformer model of the Guanella 1:4 balun – some further observations I stated:

Note that a two terminal impedance is a naive representation of many if not most antennas, popular, but a naive over simplification that does not facilitate evaluation of current balance.

An example was a recent posting above that used the model to make assertions about the behaviour of a Guanella 1:4 balun.

This article reports results of two experiments with NEC to model an ‘imperfect’ half wave dipole. It is not exactly resonant, but the main issue is that it is tilted from one end to the other, it is not parallel to the ground surface. Continue reading Modelling an antenna as a simple two terminal resistance is often naive

Last update: 12th November, 2022, 7:52 AM

Garden environmental telemetry project – part 4

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 in preparation for another RS485-LN.

The sensors are now:

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

The payload  contains a 8bit payload version number then four 16bit values for the four sensors. This is parsed by the TNN uplink formatter.

function decodeUplink(input) {
  var payver=input.bytes[0];
  switch(payver){
    case 1:
      return {
        data: {
          field3: ((input.bytes[3]<< 8)|input.bytes[4])/10,
          field4: ((input.bytes[1]<< 8)|input.bytes[2])/10,
          field5: ((input.bytes[7]<< 8)|input.bytes[8])/10,
          field6: ((input.bytes[5]<< 8)|input.bytes[6])/10
        },
      warnings: [], // optional
      errors: [] // optional (if set, the decoding failed)
      };
    case 2:
      break;
    }
  }

Above, is the Custom Javascript formatter which writes the measured values into variables fields3-field6 of the data object.

To be continued…

Last update: 9th November, 2022, 8:09 AM