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Tweeting freezer [130149-I]

Status: In progress
5379
5
votes
March 28, 2013
FreezerTwitter.jpg

 

By Marco van Nieuwenhoven

 

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

I already connected an "mbed NXP LPC1768" board to the controller. Also I added a USB connector (for firmware updates) and a RJ45 connector (for internet access).

Update 2013 March 29 Definition of the 7 segment display:

  1     2     3     4     5     6     7     8  

 ...   -a-   -a-   ...   -a-   -a-   -a-   -a- 
.   | .   | .   | |   | |   . |   . .   | |   |
.   b .   b .   b f   b f   . f   . .   b f   b
.   | .   | .   | |   | |   . |   . .   | |   |
 ...   -g-   -g-   -g-   -g-   -g-   ...   -g- 
.   | |     .   | .   | .   | |   | .   | |   |
.   c e     .   c .   c .   c e   c .   c e   c
.   | |     .   | .   | .   | |   | .   | |   |
 ...   -d-   -d-   ...   -d-   -d-   ...   -d- 
                                               
  9     0     A     b     C     d     E     F  
 -a-   -a-   -a-   ...   -a-   ...   -a-   -a- 
|   | |   | |   | |   . |   . .   | |   . |   .
f   b f   b f   b f   . f   . .   b f   . f   .
|   | |   | |   | |   . |   . .   | |   . |   .
 -g-   ...   -g-   -g-   ...   -g-   -g-   -g- 
.   | |   | |   | |   | |   . |   | |   . |   .
.   c e   c e   c e   c e   . e   c e   . e   .
.   | |   | |   | |   | |   . |   | |   . |   .
 ...   -d-   ...   -d-   -d-   -d-   -d-   ... 
 
Update 2013 March 28 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. A photo of the simulation environment has been added.

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 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 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.

Update 2013 March 17 The freezer posted it's first tweet on https://twitter.com/plugfreezer.

 

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Images
TemperatureProfile
FrontPanel
mbed Connected
Connectivity
Print Layout
Simulation Environment

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