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

IoT water tank telemetry project – HC-SR04 – first 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.

A series of tests were conducted of range to a hard surface at a distance of about 250mm and calculated ‘tank’ level and temperature plotted over time. Temperature is measured on the prototype breadboard using a DS18B20, and calculation of distance is compensated for the variation in velocity of sound with temperature. Continue reading IoT water tank telemetry project – HC-SR04 – first trial

An interesting study in the effect of fixture on impedance measurement

A chap posted a pic and some mini VNA measurement results of a resistor which he reported has a DC resistance of 80Ω.

Above is part of the pic, focusing on the ‘fixture’. The chap reports that the VNA was OSL calibrated, and we might assume that was at the SMA(M) connector (it is difficult to explain the results if the reference plane was at the VNA jack). Continue reading An interesting study in the effect of fixture on impedance measurement

A common scheme for narrow band match of an end fed high Z antenna – surely it is a 1:9 transformer?

A reader of A common scheme for narrow band match of an end fed high Z antenna commented:

…if the coil is tapped at 1/3, surely then the coil is a 1:3^2 or 1:9 transformer and the capacitor simply ‘tunes out’ the coil reactance, what is the input impedance when it has a 450+j0Ω load?

That is very easy to calculate in the existing Simsmith model.

Above, with load of 450+j0Ω, the input impedance at 50MHz is 8.78+j34.36Ω (VSWR(50)=8.4), nothing like 50+j0Ω. Continue reading A common scheme for narrow band match of an end fed high Z antenna – surely it is a 1:9 transformer?

A common scheme for narrow band match of an end fed high Z antenna

This article discusses the kind of matching network in the following figure.

A common variant shows not capacitor… but for most loads, the capacitance is essential to its operation, even if it is incidental to the inductor or as often the case, supplied by the mounting arrangement of a vertical radiator tube to the mast. Continue reading A common scheme for narrow band match of an end fed high Z antenna

Replacing the crystal in a Seiko V158-0AD0 watch

I have a Seiko V158-0AD0 which works very well, and I recently noticed the crystal was scratched more than the case… so a strong hint that it is an ordinary mineral glass crystal.

Searching the net, I could find that the Seiko part number for the original crystal is 310P03HN0 which indicates a diameter of 31.0mm but it does not have the thickness encoded simply. I could not find any articles giving the thickness of the part… so measurement was needed.

Above, the original crystal measures 1.6mm. A ‘standard’ 1.5mm sapphire crystal should be just fine. Continue reading Replacing the crystal in a Seiko V158-0AD0 watch

IoT water tank telemetry project – ultrasonic sensor – HC-SR04

This is a new project derived from IoT water tank telemetry project – part 1 , but using an inexpensive ultrasonic ranging sensor to determine the height of water in a tank or dam, and so water depth or volume.

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. Continue reading IoT water tank telemetry project – ultrasonic sensor – HC-SR04