Capacitance Meter

A capacitance meter has been constructed, based on a PIC microcontroller development board and OLED display.  A Capacitive Voltage Divider, CVD, comprising the capacitor under test, Cut, and sample/hold capacitor, Chold, of the integrated PIC ADC was used to derive the capacitance of Cut,  by the 'double sample', differential CVD measurement method.

VCHOLD1 = sample 1 voltage across the internal ADC hold capacitor.

VCHOLD2 = sample 2 voltage across the internal ADC hold capacitor.

CUT = capacitance in picoFarads of the capacitor under test.

After designing a suitable jig, the meter will be useful in determining the value of unmarked smd capacitors.

Cut is two 22pF capacitors in parallel

ADC = Analogue to Digital Converter.

LoRa WAN

A "LoRa" ( Long Range )  wireless data link had already been used in a previous project to collect soil moisture data; but was not joined to a LoRa WAN network, in which nodes ( end-devices e.g. sensors ) are connected to gateways which then connect to the network server where the data from the end-device can be displayed and accessed by other applications for long-term storage and visualisation.

The public "TheThingsNetwork (TTN)" global IoT LoRaWAN network with the "Things Stack Community edition" server were used to test the possibility of connecting a node comprising a TTGO LoRa32v2 development board, before designing future projects with sensors. Only a short text message was to be sent; "TTGOLoRa32v2 node test".

The message was successfully received by a gateway 6kms away and forwarded to the server.

The upper image shows the experimental node in a temporary location by a window. The lower image is a partial screen capture of the live data on the server console.

 

TTGO LoRa32v2 node successfully joined TTN

Live data from the TTGO LoRa32 node on the Things Stack server

 

For more information on TheThingsNetwork visit https://thethingsnetwork.org

IoT = Internet of Things

 

Digital Inclinometer

The MPU-6050 is an Inertial Measurement Unit comprising a MEMS 3-axis gyroscope and 3-axis accelerometer. The gyros provide angular velocity data; the accelerometers give relative 'g' (  acceleration due to earth's gravity ). Several were obtained, already mounted on evaluation boards. The project was to use it in a digital inclinometer. For this application, however, only the accelerometers were needed. The image below shows the setup used for developing software for the prototype. A digital angle meter was used for comparison. For the y-axis orientation in use, the inclination is displayed as negative degrees; a downwards slope.

(L) MPU-6050 evaluation board, (R) micro-controller/display board

Two versions were completed, with or without a display and having different enclosure styles, suitable for whether the inclinometer would be visible or located remotely when in use. The display version is shown in the image below. It is indicating 0 degree inclination and 1 degree roll to the right when placed on a "flat horizontal" surface.

Display version of the Inclinometer in attractive enclosure with lid

Both versions have Bluetooth functionality, enabling the inclination and roll meaurements to be displayed on a paired mobile device.

MEMS = Micro Electro Mechanical System.

USB to UART Converter

Some devices, e.g., ESP8266-01 wifi modules, GNSS receiver modules, Particulate Matter sensors and others have a 'start-stop signalling' RS232 type of serial interface for exchanging data. A USB to UART ( Universal Asynchronous Receiver Transmitter ) converter is required in order to display the data using a serial terminal program on a pc for example. Other uses include: alternative if no legacy COM port, provides a virtual COM port, provides usb connectivity, for retreiving raw data for display and parsing, connect with devices having a uart interface, connect with usb to a micro-controller uart peripheral. It's an extremely useful item.

USB-UART converter connected to ESP8266-01 wifi module

TX and RX data shown in a serial terminal application

 

 

RS485 Interface for MCUs

Micro-Controller Units ( MCUs ) typically have one or more integrated USART peripherals but lack an RS485 interface for serial communication using a twisted pair over distances of tens of metres. When required, an external interface is necessary.  Two are needed for inter-MCU communication, or a USB-RS485 protocol converter dongle to transfer data to an application on a pc for example. In the image below the breadboard used at SpacerLabs for PIC MCU project development is shown. The MCU PIC16F18875 is being used.

RS485 interfaces at either end of 4.5m twisted pair

 

RtdTerm

The SpacerLabs "RtdTerm" software enables the features and configuration settings of the MAX31865 Resistor Temperature Detector ( RTD ) to digital converter chip ( see previous post ) to be easily evaluated and experimented with. A 2-wire PT100 RTD has been connected on this occasion; 3 and 4 wire RTDs are also supported.

'RtdTermv1.06' user interface

 

 

PT-100 RTD

Resistor Temperature Detectors ( RTD ) made from Platinum (Pt) are more accurate than thermocouple wires for measuring temperature. A 2-wire PT-100 RTD was tested using a MAX31865 RTD to digital converter chip on an evaluation board, and usb-spi dongle controlled by SpacerLabs "SpiConfig v3.0" software.

The tiny PT100 RTD is just visible on the extreme right

Result of reading measurement data from MAX31865 using 'SpiConfig'

From the MISO ( master in, slave out ) bytes the temperature was found to be 19.92 C.

[ Note: PT-100 has 100 ohm resistance at 0C ].

 

 

 

SPI configurator

Used in conjunction with a usb - spi ( serial peripheral interface ) protocol converter, this tool conveniently confirms the correct spi settings used by a peripheral device prior to developing application firmware on the selected platform. The image below shows the user interface displaying the temperature data read from a MAX31855 thermocouple to digital converter. (Click on image to enlarge).

SpiConfig v3 user interface

 

 

 

Oven Temperature Checker

Measuring temperature using a MAX31855K thermocouple to digital converter chip and Lilygo TTGO T-Display ESP32 board. To be used as an "Oven Temperature Checker" ( OTC ) for comparing actual air temperature inside a domestic oven with the set value.

Type-K thermocouple connected to MAX31855 breakout board

The OTC is unusual as it also acts as a BluetoothⓇ server ( SpacerLabs_OvenCheck ) using the 'Bluetooth Low Energy'  ( BLE ) variant of BluetoothⓇ. Connecting to it with a paired BluetoothⓇ client device ( e.g., a smart phone 📱), having a suitable App installed enables the OTC ready for use. The BLE features of the OTC have been modelled on the standard service and characteristics of the BluetoothⓇ "Environmental Sensing Service", having just the one characteristic for "Temperature" exposed.

SpacerLabs "Oven_Check" App

Many general purpose BLE client App's are available. However, here at SpacerLabs, we have built our own custom App for Android devices, called 'Oven_Check', to make the process of accessing the functions of the OTC quick and easy.