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Wolfgang Hottgenroth
2018-05-25 13:44:55 +02:00
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<!-- { "title": "Integrated Thermometer and Timer" } -->
<h1>#title#</h1>
<p>
To brew green tea you need water of about 75°C. To know that your water has 100°C is easy, you can see that it is boiling. For 75°C you need a thermometer. Then you also need to take care about the brewing time. It should be usually two minutes.
</p>
<p>
There are such integrated thermometer and timer things on Amazon, but that's not me cup of tea, I decided to build one on my own. It should run on batteries, it should be small and it should make no noise (for office use).
</p>
<p>
In between I was reading "Patterns for Time-Triggered Embedded Systems" from Michael Pont. And afterwards I was curious to use such a simple cooperative scheduler instead of the super-loop, as it is common in the Arduino domain.
</p>
<p>
I used a MSP430G2553 with 10bit-ADCs, a PT1000 sensor and two seven-segment LED displays.
</p>
<p>
The code is available at <s><a href="https://bitbucket.org/wollud1969/teathermotimer" target="_blank">https://bitbucket.org/wollud1969/teathermotimer</a></s> <a href="https://gitlab.com/wolutator/TeaThermoTimer">https://gitlab.com/wolutator/TeaThermoTimer</a>.
</p>
<p>
<a href="files/img_0813-e1473432862286.jpg"><img src="files/img_0813-e1473432862286_small.jpg"/></a>
</p>
<p>
<a href="files/img_0814.jpg"><img src="files/img_0814_small.jpg" /></a>
</p>
<p>
Schematics:<br/>
<a href="files/201609091558_0001.pdf">201609091558_0001</a>
</p>
<p>
Calculation for measurement:<br/>
<a href="files/201609091558_0002.pdf">201609091558_0002</a>
</p>

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<!-- { "title": "Integrated Tea Timer and Thermometer, Second Edition" } -->
<h1>#title#</h1>
<p>
I've two offices, so I'm requiring two of this timers.
</p>
<p>
The second one I built with a three-digit display and auto-power-down and start with a push-button.
</p>
<p>
This thing consumes in operation about 20mA, which is a real lot for so few functionality, but most of the power goes into the display. I was looking for a simple LCD on ebay, but it seems that most of the LCD 7-segment display have only one common and one pin for every single segment instead of one common per digit. These are too many pins for the 2553 and I didn't want to put an additional LCD controller on the board.
</p>
<p>
However, when the thing goes in LPM4, it only consumes about 0,1uA, as it is written in the datasheet. Very important to achieve this low power consumption: an input pin requires more power than an output pin put into the right level. And of course the reference generator of the ADC needs to be shutdown.
</p>
<p>
The sources are still available here <s>https://bitbucket.org/wollud1969/teathermotimer</s> <a href="https://gitlab.com/wolutator/TeaThermoTimer/tree/SecondEdition">https://gitlab.com/wolutator/TeaThermoTimer/tree/SecondEdition</a>, look for the branch <code>SecondEdition</code>.
</p>
<p>
The schematic is more or less the same, just on digit display more and a reset push-button.
</p>
<a href="files/img_0818-e1473677307841.jpg"><img src="files/IMG_0818-e1473677307841_small.jpg"/></a>
<a href="files/img_0821-e1473677332189.jpg"><img src="files/IMG_0821-e1473677332189_small.jpg"/></a>