Month: July 2021

Measure transmission line Zo – nanoVNA – PVC speaker twin – loss model derivation

The article Measure transmission line Zo – nanoVNA – PVC speaker twin demonstrated measurement of transmission line parameters of a sample of line based on measurement of the input impedances of a section of line with both a short circuit and open circuit termination. From Zsc and Zoc we can calculate the Zo, and the complex propagation constant \(\gamma=\alpha + \jmath \beta\), and from that, MLL.

Measurement with nanoVNA

So, let’s measure a sample of 14×0.14, 0.22mm^2, 0.5mm dia PVC insulated small speaker twin.

Above is the nanoVNA setup for measurement. Note that common mode current on the transmission line is likely to impact the measured Zin significantly at some frequencies, the transformer balun (A 1:1 RF transformer for measurements – based on noelec 1:9 balun assembly) is to minimise the risk of that. Nevertheless, it is wise to critically review the measured |s11| for signs of ‘antenna effect’ due to common mode current. Continue reading Measure transmission line Zo – nanoVNA – PVC speaker twin – loss model derivation

Last update: 31st July, 2021, 2:57 PM

A template for an air filter foam element

I was somewhat frustrated that I could not easily buy air filter foam inserts for the common 25cc Chinese chainsaw. Sellers sold the housing, but no filter element in it.

So, the project is to make a template to cut a foam element that is a neat fit inside the housing.

Above is a sketch laid up over a picture of the filter cover. The template is made a little larger than the aperture so that the foam filter element compresses a little to fit. Continue reading A template for an air filter foam element

Last update: 19th July, 2021, 4:47 PM

IoT water tank telemetry project – HC-SR04 – second trial

IoT water tank telemetry project – ultrasonic sensor – #1 described an inexpensive ultrasonic ranging sensor for trial.

Above is the HC-SR04 ultrasonic ranging sensor, it was purchased for around $6 from a local eBay seller and delivered within days. Note that there are somewhat similar looking things with a second board on the back and a different interface, the basic HC-SR04 as pictured suits this project.

In this second trial, the battery saving feature has been activated. It powers the HC-SR04 on for each measurement, waiting 600ms for the HC-SR04 to stabilise. Continue reading IoT water tank telemetry project – HC-SR04 – second trial

Last update: 17th July, 2021, 8:12 AM

IoT water tank telemetry project – JSN-SR04T-3.0 – first trial

IoT water tank telemetry project – HC-SR04 – first trial mentioned an inexpensive ultrasonic ranging sensor for trial.

Above is the JSN-SR04T-3.0, a waterproof transducer on a cable and the electronics board. The protocol is HC-SR04 PWM. No specifications or datasheet were found (other than the seller’s brief description). Continue reading IoT water tank telemetry project – JSN-SR04T-3.0 – first trial

Last update: 14th July, 2021, 7:44 AM

BME280 vs BMP280

Several of my projects use Bosch BME280 sensor chips for measuring temperature, pressure and humidity.

Some correspondents have expressed problems using BME280 modules that they bought online, and it is usually because they have been cheated by online sellers misrepresenting BMP280 as BME280.

My projects that include code to initialise and read BME280  humidity will fail on a BMP280… check to see if the humidity results returned look sane. A driver may read the ChipID and fault on the ID returned by a BMP280.

The Bosch chips are usually visually different, and most clones likewise.

BME280 – temperature pressure and humidity sensor.

Above, the BME280 is a small square package, about 2.5mm each side. Continue reading BME280 vs BMP280

Last update: 13th July, 2021, 7:20 AM