True RMS Voltmeter ⌁

⚡The Root Mean Square ( RMS ) voltage is a useful value to measure as it is related to the power  ( 'heating effect' ) of the voltage. The SpacerLabs "RMSDC-1" voltmeter described here is able to measure the true RMS value of complex periodic voltage waveforms, ( not just sinusoidal ∿ ), up to frequencies of  typically 8MHz, and even if a DC offset level is present.

Measuring the output voltage of a 3V DC precision source

Central to the operation of the RMSDC-1 is a highly accurate RMS to DC converter chip which produces a DC voltage equivalent to the RMS value of the input voltage. This DC voltage is sampled by a separate 10-bit analogue to digital converter ( ADC ) so that the voltage can be displayed. Also a dB output is available which has been calibrated to give the dB value of the input voltage being measured relative to 1V ( 1V = 0dBV ). For DC voltages the RMS value is the same as the DC value. So the RMSDC-1 can be used as a DC voltmeter. Both AC and DC input coupled signals can be measured; the latter allowing any DC offset to be retained. An active analogue filter of the Sallen-Key type can switched in to reduce any potential inaccuracy due to AC ripple at 2X input frequency.

An attractive 3-D printed front panel can be fitted

A front panel has been designed and printed to give the RMSDC-1 a very smart appearance. The front panel also serves to support the RMSDC-1 vertically. The display module is a 2X16 LCD with a white or yellow/green back-light. 

 

AD9850 DDS Module with mobile App configurator

📶The Analog Devices Inc. AD9850 is a 32bit CMOS Direct Digital Synthesiser ( DDS ) device. Evaluation circuit boards with the device already mounted are widely available at low cost. However, in order to use the device ( perhaps only a quickly assembled frequency source is required ) a means still has to be provided of uploading to it 5 bytes of configuration settings, also a display to show the frequency and a rotary encoder for tuning. In the past at 'SpacerLabs' we have used a SPI-USB dongle and pc terminal software to acheive this.

📳A different and even more convenient method has recently been devised using an ESP32 micro-controller and our custom App for mobile devices📱called "DDSTerm". The App generates the 5 configuration bytes required from the user input frequency and phase data, then sends to the ESP32 using BluetoothⓇ. The ESP32 uploads the bytes using the SPI to the DDS board. The desired frequency [ ∿ ] is output. In the image example below frequency is 11.501MHz & bytes hexadecimal 178DD617C4.

App 'DDSTerm_v1.06' opened

The image below shows the hardware setup used during development, comprising a typical ESP32 micro-controller in a 3-D printed case connected to the AD9850 DDS evaluation board mounted on a test-jig. The test-jig is not essential as the DDS board has pin-strip headers.

(Left) AD9850 board on test-jig, (R) ESP32 micro-controller inside enclosure

𝌕The Android App "DDSTerm" and firmware for the ESP32 are available from us. Contact us by email or use the form below to receive more information. Note that AD9851 DDS boards are also supported.

SPI = Serial Peripheral Interface ( 3-wire bus )

 

Cyclometer 🚵

The SpacerLabs "Cyclometer" is a cycle 'trip-computer' which provides a cyclist 🚴 with data on number of wheel revolutions (Revs), distance travelled (Kms), average speed (Av.Kph) and current speed (Kph). It comprises a display unit, magnetic switch and magnet. 3-D printed enclosures for these separate parts give the Cyclometer a smart appearance. The Cyclometer is powered by an internal 3.7V rechargeable Li-Ion polymer battery.

Cycle wheel revolutions are detected by the magnetic switch which is closed and opened by the magnet fixed to a wheel spoke as it passes by close to the switch. The switch is wired to the display unit which counts and displays the revolutions. The distance travelled is calculated from the number of wheel revolutions and the wheel outer circumference measurement. A free-running internal milli-second timer allows the cycle speed to be determined.

The Cyclometer display unit

The Cyclometer display unit is unusual as it also acts as a BluetoothⓇ server ( SPACERLABS_CS ) 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 Cyclometer ready for use. The BLE features of the Cyclometer have been modelled on the standard service and characteristics of the BluetoothⓇ "Cycling Speed & Cadence Service", though no cadence, ( crank ), data are required by the current version of the Cyclometer. An additional characteristic has been provided to support the wheel outer circumference measurement.

The SpacerLabs 'Cyclometer' App

Many general purpose BLE client App's are available. However, here at SpacerLabs, we have built our own custom 'Cyclometer' App for Android devices to make the process of updating sensor location and wheel size quick and easy !

Solar UV Radiation Meter🌤

Frequent or prolonged exposure to high levels of solar 🌞 ultra-violet ( UV ) radiation can damage the human skin.

The SpacerLabs solar 'UV Radiation Meter' ( abbreviated UVRM ) provides a way to measure the radiation and display the result as the UV Index and UV Level. Informed decisions about appropriate precautions can then be taken if necessary. 😎🤠

The UVRM is based on the Silicon Labs SI1145 'UV Index sensor', together with a 32bit micro-controller, blue 0.96" 128x64px OLED display module and power management system. The UVRM is powered by an internal 3.7V rechargeable Lithium battery, which can be charged in-situ via the micro USB connector. A custom 3-D printed blue & white hand-held enclosure gives the UVRM a smart appearance.

UV Index ( zero to 11+ with a resolution of 0.01 ), and UV Level are displayed according to the W.H.O definitions; Low, Moderate, High, Very High & Extreme. The SI1145 also derives a "Visible Light Index" ( VIS ) and an "Infra-Red Index" ( IR ). These indices are not displayed directly by the current versions of the UVRM.

UVRM displaying an indoor UV reading

Two main options have been developed allowing the UVRM to be used as a stand-alone device when extended battery life is important or the option of wireless connectivity using BluetoothⓇ.

SpacerLabs has developed a custom App called  "Light_Meter" to connect to the UVRM using BluetoothⓇ communications.

The SpacerLabs 'Light_Meter' App

Using one of the BluetoothⓇ versions of the UVRM with a paired and connected mobile device running the App makes it easier to view the data in some outdoor situations 🌞. The VIS and IR indices are also exposed.

 

( W.H.O = World Health Organisation )

 

Multi Sensor Air Quality Monitor

An inexpensive domestic 'Air Quality Monitor'  ( abbreviated AQM ) has been modified with additional sensor support, display module and 32-bit micro-controller.

The original AQM, ( made in China ), uses a Cubic PM1006 Particulate Matter sensor to determine the PMx ( x =  microns ) particulate matter concentration in the air and changes the colour ( green, yellow or red ) of an illuminated indicator accordingly. This feature has been retained in the SpacerLabs modified versions.

The modified versions measure PM1, PM2.5 & PM10 and, optionally, have either a CCS811 sensor or AHT20 sensor also fitted to provide TVOC & CO2 or temperature & humidity data as well. The measurement data are displayed on a blue or white 128x32 pixel OLED display. Firmware which controls the sensors and the display is uploaded to the micro-controller via a micro USB connector.

AQM version PM1006/CCS811

AQM version PM1006/AHT20 will be deployed in the kitchen where airborne particulate matter ( smoke ) and high humidity caused by cooking can be monitored.

AQM version PM1006/CCS811 is suitable for a workshop environment where CO2 & TVOC could be present, in addition to particulate matter.

A SpacerLabs App, called "Air_Quality", has been designed, so that the PM1, PM2.5 & PM10 measurements can be viewed on a mobile device, using BluetoothⓇ communication. The PM2.5 concentration value will change colour in the same way as the illuminated visual indicator on the original domestic AQM.

SpacerLabs 'Air_Quality' App

The AQM can be powered by a USB charger connected by a cable with a USB-C plug.

The micro-controller also has built-in wifi as well as BluetoothⓇ. This opens up the future possibility of integrating the multi-sensor AQM into a 'smart home' network.

TVOC  = Total Volatile Organic Compounds ( paint, solvents etc ).

Touch Screen for the Greenhouse Gas Monitor

Nowadays it seems almost obligatory that electronic gadgets have a touch screen display user-interface. Such a display has now been incorporated in a Greenhouse Gas Monitor ( see 28 July 2022 ).

This particular display type is a 2.8" 240x320 pixel touch panel display with SPI and using the ILI9341 driver chip. On the back is an SD card slot. Cost when purchased was just under GBP11.

Either Methane ( CH4 ) or Carbon Dioxide ( CO2 ) concentration data can be displayed separately in real-time by tapping on a displayed 'button', without having to connect to the 'ThingSpeak' or 'Ubidots' cloud repositories as before in order to view the data; the cloud would still be required, however, for data storage ( unless SD card used ) and processing.

An experimental version comprising the display and an ESP32 micro-controller development board ( with new firmware ) mounted on a prototyping board was assembled and connected to the same pair of outdoor gas sensors ( MQ-4 & MQ-135 ) used previously.

The Methane CH4 concentration is selected

The Carbon Dioxide CO2 concentration is selected

( SPI = Serial Peripheral Interface )