SCT-010-000 current transformer protection

The YHDC SCT-010-000 clip-on or non-invasive current transformer is widely used in DIY energy monitor applications, and is readily available on eBay for A$6 including post.

A key issue with current transformers is that current in the primary winding will cause excessive voltages in the secondary winding unless the secondary winding is suitably loaded. The broad rule of thumb is NEVER disconnect the output connections whilst current flows through the primary.


YHDC’s website is typical of Chinese web sites, and I could not find a datasheet for information on the internal circuit and possibly internal protection.
Continue reading SCT-010-000 current transformer protection

Review of Hantek DSO8102E hand held oscilloscope

This article is a brief review of some issues that were found with initial testing of a Hantek DSO8102E two channel 100MHz hand held oscilloscope.

The DSO8102E is a member of the DSO8000 series (DSO8060, DSO8070E, DSO8100E, DSO8150E, DSO8200E), and shares most specifications across the series.

The specifications are very impressive, and price at just under $1000 for a Chinese brand seemed reasonable (hand held oscilloscopes are expensive compared to bench oscilloscopes).

The test scenario was a practical application, observation of the data traffic to/from a DHT22 temperature and humidity sensor in the project ESP8266 IoT DHT22 temperature and humidity – evolution 2. Continue reading Review of Hantek DSO8102E hand held oscilloscope

ESP8266 IoT DHT22 temperature and humidity – evolution 3

This article documents a first project with the Espressif ESP8266 in its third evolution (based on ESP8266 IoT DHT22 temperature and humidity – evolution 2).

The objective is a module that will take periodic temperature and humidity measurements, and in this evolution publish them using a RESTful API.

Evolution 3

The example platform used in this article is a Wemos D1Pro. In this case, the D1Pro is configured for an external antenna, and a modification is made to the board to add a 1N34A diode for the deep sleep reset circuit (NodeMCU devkit V1 deep sleep). A three pin right angle header to the top of the board (as seen) and another on the underside on the opposite edge to get GND, +5, +3, and D4 for the DHT22 data wire. There is less than $20 in parts in the pic above. Continue reading ESP8266 IoT DHT22 temperature and humidity – evolution 3

High gain external antenna for Wemos ProMini

I have some IoT projects that would benefit from range afforded by a better antenna than the on-board antennas in most ESP8266 modules.

The Wemos ProMini has an on-board IPX socket for an external antenna so it is a candidate. Note that a 0R 0603 resistor needs to be removed and another or a wire link soldered in to route the RF to the IPX socket.

Above the Wemos ProMini with a 7dBi SMA-RP antenna ($1.80) and flylead SMA-R(F) to IPX (M) ($1.00).  Continue reading High gain external antenna for Wemos ProMini

A search for some mid power white wide angle LEDs

I have a project which needs some mid power (~3W) white wide angle (120+°) LEDs.

The obvious source ie eBay which means running the gamut of Chinese sellers, sellers who rarely understand the product they sell and probably expect the same of buyers.

Buying electronic components on eBay

Component sales tend to fall into categories:

  1. those with headline descriptions that have very brief description of characteristics; and
  2. those whose descriptive content claims well known part numbers for which datasheets can separately be found;
  3. those with detailed specifications offered.

In the case of category 1, it is very hard to have confidence that the components will deliver required performance, and headline descriptions on eBay are often used as competitive search keywords and do not apply to the goods on offer. These are probably best skipped unless they are the only option.

Category 2 provides a better option, and the question then on delivery is whether the goods are compliant with the part number offered. There is a considerable risk of counterfeit or fake parts that are not equivalent to the claimed part number, even where brand names are cited.

The third category can provide suitable product, but it takes some leg work, more than ‘due diligence’ to check the description for consistency and form an idea about its reliability, fit to the requirements and then value for money, seller reputation etc. This can be a lot of work for a few dollars worth of parts, but is a better option than category 1.  Continue reading A search for some mid power white wide angle LEDs

ESP8266 relay module review – Yunshan WiFi relay

After scouring eBay for a packaged esp8266 with 220V 10A relay, two products were identified:

  • Yunshan WiFi relay; and
  • LC Technology relay.

As is usually the case, finding a schematic and specifications is very difficult and the sellers were of no help (no surprises).

The LC Technology device was offered with indistinct pics that hinted it had a 8Mb flash chip, ESP8266EX processor, and a STC 15F104 8 bit processor on board for some unidentified purpose.

A schematic was eventually located for the Yunshan board, and from pics it appeared to have a 12E module on it which hinted the flash size.

A Yunshan module was purchased for about $10 posted, and it was indeed a 12E with flash-id 4016, so 4MB of flash memory.

The board does not incorporate a USB-TTL adapter which is a nuisance not just requiring an external adapter for programming, but there is no integration of the RTS and DTR signals as in the NodeMCU devkit. Adding a quality USB adapter (eg CP2102) would not increase the price a lot, you can keep the CH340G etc). Continue reading ESP8266 relay module review – Yunshan WiFi relay

Reset helper for NodeMCU ESP8266 modules

A common scheme for Lua scripted NodeMCU modules with automaticlly start the script init.lua is to incorporate some logic to test the condition of a GPIO pin to determin wether to boot to the application or drop to the lua prompt for programming etc. In fact the scheme can be elaborated to provide a simple multi level selection based on the time the input condition is applied.

The obvious pin to use is the pin that commonly has a “BOOT” or “FLASH” button on it, GPIO0 or D3. It is used to activate the ESP8266 boot loader if it is low during boot, so it must be left high at boot to allow the lua interpeter to run, but it can be pulled low shortly after boot up and tested from init.lua.

An example init script follows.

print("\n\nHold Pin00 low for 1s t0 stop boot.")
print("\n\nHold Pin00 low for 3s for config mode.")
if == 0 then
  print("Release to stop boot...")
  if == 0 then
    print("Release now (wifi cfg)...")
    print("Starting wifi config mode...")
    print("...boot stopped")
print("Starting app.lua")


Above is a pic of the helper. The DIP switch allows selection of the BOOT pulse in 1s increments. It has four connections, ground, Vdd, BootOut, and Reset (optional). The button near the DIP switch resets the helper which in turn will apply a 10ms reset pulse to the Reset line. Continue reading Reset helper for NodeMCU ESP8266 modules

ESP8266 IoT DHT22 temperature and humidity – evolution 2

This article documents a first project with the Espressif ESP8266 in its second evolution.

The objective is a module that will take periodic temperature and humidity measurements and publish them to an MQTT message broker.

This inital implementation is very basic, it is largely configured in code, though it does use DHCP. Later extensions might include a web interface for configuration of WLAN parameters etc, but for the moment the emphasis is assessment of reliability given some reports on the ‘net.

Evolution 2

The original design embedded key configuration variables in the main source code for simplicity in getting the code working.

Evolution 2 separates configuration variables from code, and provides a web interface for configuring the most common variables. The screenshot above shows the configuration screen including the use of a datalist on the SSID input field.


A module was purchased with on board CP210x USB to serial chip. The only other component needed was the DHT22 digital temperature and humidity sensor.

NodeMCU was chosen for the ESP2866 firmware because of the inbuilt support for ‘interesting things’, including the DHT22.

Above is a breadboard of the system for development. The board had a 4MB (32Mb) flash chip on it. Continue reading ESP8266 IoT DHT22 temperature and humidity – evolution 2