Friday, November 17, 2017

Oh no, not another wifi thermometer.

I know. It is stupid. And at first I was not even sure why I was building it. As the internet is paved with ESP-Weatherstations and thermometers. And why on earth is the weather so interesting. Just look outside and you know what it is like. And then a reason came up. For testing all kind off IOT cloud services I needed a device that would constantly provided some data and what is easier as a thermometer to provide data.  However I had some demands.

It should be really low cost. and it is !!! I used an ESP-01 (1.57 euro) a Dallas 18b20 temperature sensor (0.98 euro) a LM317 voltage regulator (0.08 euro) , some resistors (about 0.05 euro) and a USB cable (about 1 euro). That sums up to 3,68 euro. Add some stripboard and wire and there is your complete thermometer for about 4 euro.
Naturally I printed the casing myself.

This project should not take more as a few hours to build. I made a prototype on a breadboard and when that worked I transferred it to some stripboard. Programming was done in the unmatched easy ESP-Basic language.

Before we start.
Before we really start with this project I want to point out some basic knowledge articles I wrote that helps you understand how all fits together.
First read about the LM317T voltage regulator which allows you to provide your project with any voltage you might need. Read that story by clicking here.

And please read the introduction article to ESP-Basic which makes developping ESP8266 projects a piece of cake. The introduction article runs you through flashing ESP-Basic and using the web-based editor to writing your first programs.

Let's go.

Powering the project.

The ESP-01 works at a 3.3Volt power level. And the Dallas Temperature sensor fortunately also does so. I am going to power this project from a USB power source (be it a computer, mains adapter or powerbank). So the USB power, which is 5 volt has to be reduced to 3.3 volts.

As stated above I am doing this by the use of a LM317T voltage regulator. 5 Volt is supplied and reduced to 3.3 Volts.

As you can see from the schematics above we will need a resistor of 1.2K and a resistor of 2K to achieve this. Like  I said above: for more information about this read the article about the LM317T.

The breadboard shows you the setup.

The ESP side

For flashing ESP-Basic and programming I used my ESP-01 programming board which I described in detail in the story you will find by clicking here.

As you know the Dallas 18B20 needs a pull-up resistor of 4K7 to function. So I attached my programming board to a small breadboard on which I placed the resistor and connected the Dallas temperature sensor.

At first to make life easy I soldered some paperclip wire to the Dallas 18b20 wires so I could easily fit them on the breadboard. The paperclip trick is one I use often. For those of you not familiar with it click here to read the story. Later on I replaced them with dupont wires cut in half and soldered to the Dallas 18B20 wires.

 So when this all functioned I completed the setup on the breadboard.

And when all functioned as it should I put it on two left-over pieces off stripboard.

The program.

 Timer 5000, [start]  
 wprint "<!DOCTYPE html>"   
 wprint "<html> <body>"  
 wprint |<body style="background-color:greenyellow;">|  
 wprint |<H1><span style="color: red;">|  
 wprint " A thermometer"  
 wprint "</H1>"  
 wprint "</span>"  
 wprint |<H2><span style="color: blue;">|  
 wprint "Temperature is now "  
 textbox test  
 a = "background-color:greenyellow;"  
 a = a & "display:block;width:80px;"  
 a = a & "border-style: hidden;"  
 a = a & "font-size: 22px;"  
 a = a & "font-weight: bold;"  
 a = a & "color: fuchsia ;"  
 cssid htmlid(), a  
 wprint "</span>"  
 wprint "</H2>"  
 test = temp(0)  
 test = ((int(test*10))/10)  

The program may look complicated but regard it closely and you will see that in reality it is not. There are some neat tricks in it though.

Let's simplify it first.

There are just 3 lines that actually are the real program core:

test = temp(0)
test = ((int(test*10))/10)

The first line reads the Dallas 18B20 temperature sensor. And the second line rounds it to 1 decimal.

textbox test

This line actually puts the temperature on the screen. Those are the three core lines. All that follows is just pimping it up.

Timer 5000, [start]

To make the program check the temperature each 5 minutes we use the Timer command as you can see in the line above.

wprint |<body style="background-color:greenyellow;">

This sets the background of the web-page in the color "greenyellow"

a = "background-color:greenyellow;"
a = a & "display:block;width:80px;"
a = a & "border-style: hidden;"
a = a & "font-size: 22px;"
a = a & "font-weight: bold;"
a = a & "color: fuchsia ;"
cssid htmlid(), a

That is an important block of CSS code.
What it actually does is to hide the contour of the textblock, give the textblock the same background as the webpage has and gives the text in the textblock a contrasting colour.
All this together hides the textblock from the screen and makes it look as if the text is printed direct on the webpage. And that is a really nice trick.

And here is the end-result.


The casing is identical to the casing I made for the PIR alarm (click here to look at that project).

 The difference is that the lid has no opening for the PIR. It is just massive

As you can see the case is far to large for such a small stripboard and therefore has one advantage: you can also power this project  with AA batteries.

That's it.

All that rests is to give you the links to the STL files so you can replicate or adapt this to your own needs.

Till next time, have fun

Luc Volders