## IoT water tank telemetry project – ultrasonic sensor

The code developed for support of some ultrasonic sensors has been merged into the original tanklevel project at https://github.com/owenduffy/tanklevel. A lot of refactoring to provide to the change.

So far, support is provided for HC-SR04 (and things that emulate its PWM mode), MB1242 (and emulations like GY-US42v2).

A work in progress…

## IoT water tank telemetry project – GY-US42v2 – first trial

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

Above is the GY-US42v2 ultrasonic ranging sensor, it was purchased for around $14 on Aliexpress delivered within 10 days. Continue reading IoT water tank telemetry project – GY-US42v2 – first 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. 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

## 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.

## IoT water tank telemetry project – part 4

After a long hiatus… the project activity resumes.

Boxing is underway, and the code has been revised to use a BME280 sensor replacing the DHT sensor. The BME280 is a better sensor (less jitter), and is also capable of barometric pressure if that is of interest.

Experience has been that 18650 cells do not last when exposed to extreme temperatures in solar powered modules like this, so a single cell pouch 2000mAh LiPo will be used (as in the battery trials).

The code has been refactored to make measurements before starting the WiFi as WiFi activity injects noise into the ESP8266 ADC.

The nodemcu core was updated as part of this process.

## Interpolation

The system is easy to calibrate in terms of stored water volume for containers with vertical sides where the change in volume with level is uniform… but there are lots of applications where that is not true, natural dams for example.

Above is a plot of volume versus depth of water for a container like a spherical bowl. The interpolation line is a cubic spline interpolation based on the six input data points, it is of course a very good fit to those points but would appear to be a good estimator of the regions between.

The code now contains a facility to perform a cubic spline interpolation of a small number of data points over the expected range of depths.

Entry{0.000,0.000}
Entry{1.000,313.112}
Entry{2.100,1375.744}
Entry{3.000,2799.159}
Entry{4.000,4959.528}
Entry{5.000,7723.082}


Above, a set of six points (as in the chart) in the format required of the code in a file named dam.xy.

The code calculates and stores an intermediate data file <name>.cstable if it does not exist for more rapid calculation. If the .xy file is updated, the corresponding .cstable file needs to be deleted.

The init.lua file is augmented to call a transform function from the httpreq function which customises the HTTP request.

function transform()
dofile("csinterp.lua")
if level<0 then level=0 end
volume=csinterpolate("dam",level)/1000
volume=string.format(meas_fmt,volume)
print("Volume: ",volume)
end

function httpreq()
--  req=rest_url.."?api_key="..apikey.."&field1="..level.."&field2="..temperature.."&field3="..humidity
transform()
req=rest_url.."?api_key="..apikey.."&field1="..volume.."&field2="..temperature.."&field3="..humidity
body=""
print("req:"..req.."\nbody:"..body)
return req,body
end


Above, the transform function fetches the function definitions for the cubic spline interpolation, and calculates an interpolated volume from the measured level (or depth) value.

Above is a trial run using a calibration generator for the level input, and its conversion to current volume of the storage.

## Hardware

One of the possible paths this project might follow was to use LoraWan… but experience with LoraWan has not been positive, particularly issues with the Laird gateway.

Above is the enclosure, an electrical box with transparent lid. The PV array is mounted inside the lid, the cheap Chinese ones tend to degrade too quickly when exposed to the elements. There is room in the box for a 2000mAh 1S Lipo battery. The switching circuit for the 24V DC-DC converter is mostly on the Veroboard under the (red) DC-DC converter (powers the 4-20mA loop). The module at lower left is a 1S battery management / protection board.

The resistor diagonally across the Wemos module is the 4-20mA sense resistor wired from A0 to ground. Experience is that locating the resistor on-board reduces the errors due to variable contact resistance through the module header pins.

If temperature / humidity monitoring is desired, a BME280 module plugs into the header near the antenna, but it needs to be remote from the box which gets quite hot in the direct sun.

The implementation supports easy development and update, if the battery and solar cell are disconnected, plugging a computer into the USB port on the Wemos board allows update and normal operation / testing.

## Ferrite cored inductors at HF – flux, loss and saturation

I see online experts opine that small signal characteristics (eg complex permeability curves) of ferrite toroids are not valid for applications such as RF common mode choke in transmitting antennas.

Others opine that saturation is a practical design limit, and for example that Bs/2 is a safe / appropriate design target.

Let us consider a ferrite cored inductor at 7MHz. The inductor comprises 11t on a 11t on Fair-rite 5943003801 (FT240-43) toroid. This is a medium to high permeability ferrite material, and for that reason, has significant loss at HF. Higher and lower permeability materials are fashionable at different times, the higher permeability #31 mix is fashionable at this time.

I will work in MKS units.

Above is Fair-rite’s B-H curves for #43 material. Let’s take saturation flux density Bs to be 1500gauss or 0.15T. Continue reading Ferrite cored inductors at HF – flux, loss and saturation

## SNTP synchronised clock v1 – boxing it up

The SNTP synchronised clock (ssc) is an ESP8266 based time of day clock with an LED display.

The code is fairly mature, and the boxed prototype will be build with a large 4 digit 7 segment LED display (1.2″ or 30mm) using the HT16K33 driver chip.

The prototype will be housed in an ABS Jiffy box, and a new lid cut from dark red transparent acrylic on the CNC router.

Above is the sketch of the layout. The screw holes in the display are M1.6, and there is no clearance for larger screws. Continue reading SNTP synchronised clock v1 – boxing it up

## SNTP synchronised clock v1 – display options

The SNTP synchronised clock (ssc) is an ESP8266 based time of day clock with an LED display.

Code development progresses and a working prototype exists with three display options.

## Directly supported 4 digit 7 segment LED displays

Several common driver boards are supported directly by the source code, most of these and variants can be purchased online for small money.

### HT16K33

Above is a large 4 digit 7 segment LED display (1.2″ or 30mm) using the HT16K33 driver chip. Continue reading SNTP synchronised clock v1 – display options