During the last months my freezer has stopped working 3 times resulting in a TweetingFreezer_TwitterProfiledefrost of it’s complete content. This project describes how I tend to fix it.

Update 2014 Januari 24 – Twitter has suspended SuperTweet. This is the intermediate library I need to send a tweet into the world. Now I need to find a library which does support tweeting via OpenAuth.

Update 2013 August 15 – Schematic in Eagle Here is the schematic of the original schematic which I finally have drawn in Eagle.

TweetingFreezer_Schematic
Update 2013 August 14

Goals for cooperation within MADspace and Elektor Magazine :

1. Describe schematics

2. Make operational firmware

3. Connect to internet and test

Assignment: Ask people in MADspace to join or to advice this mechanics project.

Update 2013 March 28 – Setting up simulation environment It is a lot of trouble to go to the freezer upstairs and connect the laptop. That is why I created a simulation environment to measure the 7 segment display. One mbed controller is used to simulate the 2 multiplexed 7 segment displays and the second one is used to make the algorithm to read the content of the display.

The solution to measure the voltage of the button signal is indeed to create a resistor divider to measure the correct voltage (corrected for 3.3 volt). To be able to generate a new button signal for the 5 volt controller is the use of an opamp. When the opamp (lm358) gets a supply voltage of 5 volt, the max generated output is 3.7 volt (max dynamic range) and that is just not enough. The supply voltage for that opamp has to be higher than the 5 volts and I hope the voltage before the voltage regulator is high enough to compensate for a dynamic range problem with the Opamp.

 

Update 2013 March 27 – Connected button signals to the microcontroller Tried to measure the button signal line with a 3.3v controller. The problem is that the system is designed for 5 volt and it is not possible to differentiate the 3.33 V from the 5V. Need to add a resistor divider to be able to correctly measure which button is pressed. Also need to add an opamp to be able to emulate the buttons. The output of the analog output must be amplified by a factor (5 div 3.3).

Update 2013 March 23 – Profiling temperature curve Completed temperature profile including hysteresis ranges per settable temperature. Ranging from -14 C up to -24 C. See picture (TemperatureProfile) for temperature chart. In the chart the temperature has been captured, but it is a reflection of it’s analog value. Still need to find out which analog value corresponds to which exact temperature.

TweetingFreezer_TemperatureProfile

Update 2013 March 17 – Connect microcontroller to the internet and send tweets The freezer posted it’s first tweet on https://twitter.com/plugfreezer. I already connected an „mbed NXP LPC1768” board to the controller board. Also I added a USB connector (for firmware updates) and a RJ45 connector (for internet access).

TweetingFreezer_MBEDconnected

TweetingFreezer_Connectivity

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