## Calibration of the 4-20mA input

This article is a tutorial on calibrating the 4-20mA input which is designed for flexibility that is achieved through exploitation of the calibration.

The input device for this tutorial is a Pt100 RTD temperature sensor and inexpensive Chinese Pt100 – 4-20mA converter (loosely) calibrated for -50-150°. The Pt100, the converter, the load resistor, the divider resistors on the MCU board, and the MCu voltage reference all introduce error which is compensated in this end to end calibration procedure.

For this demonstration, two scenarios are measured:

1. probe in still air whose temperature is captured with an accurate thermometer; and
2. probe in boiling water whose temperature is calculated from known altitude and barometric pressure.

Another option would be to use a container of water filled with ice to obtain close to 0° for scenario 1… you don’t need a triple point cell for the end system stability and accuracy.

## Temperature of boiling water

No, we are not boiling an egg, but the results include the temperature of the boiling water under current altitude and pressure. Continue reading IoT water tank telemetry project – part 2

## IoT water tank telemetry project – part 1

This is the first in a series of articles describing a simple maker / DIY IoT water tank telemetry system.

## Design criteria

• capture water depth, temperature and relative humidity;
• IoT connectivity;
• solar / battery powered;
• wireless connection;
• use existing inexpensive electronic modules.

Design choices made initially:

• 4-20mA water pressure sensor for depth measurement;
• ESP8266 Wemos D1 mini pro for the MCU and wireless elements;
• NodeMCU / Lua software environment;
• external antenna for improved WiFi range;
• 6V 100mA PV array;
• module with TP4056 batter charger and cell protection chip;
• 2500mAh 18650 cell;
• AM2320 temperature and humidity sensor;
• bipolar transistor switch for boost converter;
• Thingspeak RESTful interface for data accumulation and presentation.

## Block diagram

Above is a block diagram showing the major system components. Almost all of the electronics is on easily obtained low cost electronic modules source from eBay, assembled on a Veroboard backplane. Continue reading IoT water tank telemetry project – part 1

## ESP8266 remote power display for energy monitor – EV3 – 5V display

ESP8266 remote power display for energy monitor – EV3 documented an evolved design for a real power display using emontx3 / emonhub / mqtt. This article documents an adaptation to use a 5V display module (for higher brightness). The ESP8266 is not 5V tolerant, so a logic level converter is needed.

## Hardware

The remote power display uses a Wemos D1Pro module, a common 5V 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit, and a common 3V/5V logic level converter between them.

Above, the Wemos D1Pro prototype with wires attached to the HSPI and power pins. A 1k pull=down resistor is soldered between the D8 and GND pins under the D1Pro board. Continue reading ESP8266 remote power display for energy monitor – EV3 – 5V display

## ESP8266 remote power display for energy monitor – EV3

ESP8266 remote power display for energy monitor and ESP8266 remote power display for energy monitor – EV2 documented a design and some variations for a real power display using emontx3 / emonhub / mqtt. This article documents an evolution to use the ESP8266 HSPI port for much higher speed writing of the LED display, high enough to be later adapted for multiplexed displays.

## Hardware

The remote power display uses a ESP8266-12E devkit 1.0 module, a common 3.3V 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit. The particular LED module has sufficient space to mount the ESP8266 inside the module.

Above, the interior of the module that suits the implementation. Continue reading ESP8266 remote power display for energy monitor – EV3

## ESP8266 remote power display for energy monitor – EV2

See ESP8266 remote power display for energy monitor – EV3 for an update…

ESP8266 remote power display for energy monitor documented a design and some variations for a real power display display using emontx3 / emonhub / mqtt. This article documents a simple compact implementation.

## Hardware

The remote power display uses a ESP8266-12E devkit 1.0 module, a common 3.3V 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit. The particular LED module has sufficient space to mount the ESP8266 inside the module.

Above, the interior of the module that suits the implementation. Continue reading ESP8266 remote power display for energy monitor – EV2

## ESP8266 remote power display for energy monitor

This article documents remote power display for an energy monitor system based on emontx3 / emonhub / mqtt.

The remote power display connects via WiFi and subscribes to a topic on a MQTT server, updates are published every 10s with data from the emontx3 by emonhub.

## Hardware

The remote power display uses a Wemos D1Pro ESP8266 module, a common 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit, and a simple 3V/5V level converter between the two (see above shrink wrapped in the cable from the D1Pro to the display).  Continue reading ESP8266 remote power display for energy monitor

## 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

## 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