## 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.

## 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.

## Stacking two ferrite cores of different permeability for an RF inductor

One of the magic ham recipes often proposed is to stack two ferrite cores of different permeability for an RF inductor, but an explanation is rarely offered, I have not seen one.

## An explanation

Starting with some basic magnetism…

The inductance of an inductor is given by $$L=N\frac{\phi}{I}$$.

For a closed magnetic circuit of high permeability such as a ferrite cored toroid, the flux is almost entirely contained in the core and the relationship is $$\mathcal{F}=\phi \mathcal{R}$$ where $$\mathcal{F}$$ is the magnetomotive force, $$\phi$$ is the flux, and $$\mathcal{R}$$ is the magnetic reluctance. (Note the similarity to Ohm’s law.) Continue reading Stacking two ferrite cores of different permeability for an RF inductor

## ESP8266 IoT BME280 temperature, humidity and pressure – 06/2021 update

ESP8266 IoT BME280 temperature, humidity and pressure described an IoT project. This article documents an update for newer nodemcu core (NodeMCU 3.0.0.0) and the revised support for BME280 (the older method having been deprecated).

This project is based on ESP8266 IoT DHT22 temperature and humidity – evolution 3, but uses the Bosch BME280 temperature, humidity and pressure sensor. The BME280 has been around for a couple of years, though recently, modules using the chip have become more expensive on eBay, around \$10. If you find BME280s listed for much less than that, it is probably Chinese cheats doing a bait and switch… delivering BMP280 (pressure only). Continue reading ESP8266 IoT BME280 temperature, humidity and pressure – 06/2021 update