The DST1020 targets the market for inexpensive digital thermostats, the most popular being the STC1000. There are two novel features to the DST1020:
- uses DS1820B digital temperature sensor (well probably a Chinese clone);
- two line display shows PV and SV simultaneously.
The DS1820B should be considerably more accurate and overcome the significant error in the conversion of NTC resistance to temperature in the other thermostats (experience is that the approximation used for the NTC characteristic is simple and inaccurate).
It is sold with brief and inadequate / incorrect user instructions.
Above, the front of the DST1020.
Above, the label of the DST1020.
Above, the interior front PCB of the DST1020.
Above, the topside of the main PCB of the DST1020. Note the relays.
The keen observer will note it uses a switched mode power supply (bottom left), implied by the voltage rating.
I could not find an English language datasheet on the JEP3F-12VDC-A relays. The label on the relays claims 10A AC current rating, it is almost certainly for resistive loads, and motor loads might be more like 4A. The relays are physically small compared to those in many of this sized thermostat.
Above, viewed from 15° above, the top line of LCD segments is obscured by the escutcheon. A similar problem exists viewing from below, the display must be read within about 5° of right angles to the front face, quite limiting and worse than bad LCDs.
The picture above from the Aliexpress item listing is not consistent with the display cutoff in the previous picture, typical Chinese deception.
The DUT was powered and the temperature calibration checked at 12° and 77°, and it was within 1° of correct, quite good for most purposes and far better than NTCs tend to be.
Having powered it radiated RF interference was evaluated. It is rotten with RFI, much like the STC1000 (which was banned from sale by the regulator in NZ due to RF emissions). The device takes a couple of seconds from power on before the display lights up, and the RF noise starts at the moment that the display lights.
The 12VDC version may not have a switched mode power supply, and might not have the RF noise associated with such, but the delay in the start of the noise hinted it is from the microcontroller and display… which exist in the DC version.
For my purposes, I usually use Inexpensive Chinese thermostat – MH1230A. It does not use a switched mode power supply, it does not make substantial RF interference, it has a large relay, they have proven reliable but accuracy of the NTC characteristic curve is wanting.
In summary, the DST1020 is
- without clear instructions;
- more accurate than similar NTC based thermostats;
- rotten with RFI;
- more difficult to read the display;
- no mention of the controls you may need if controlling a compressor.