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michka:research:microbial_fuel_cells:brussels7 [2017-09-20 17:26] – michkamichka:research:microbial_fuel_cells:brussels7 [2017-09-20 17:54] (current) – michka
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 ====Abstract==== ====Abstract====
  
-To be updated +   * Paul prototyped and made a series of clay pots to host our MFCs. 
- +   * Paul designed the final version of the robots, and built the first one. 
-   * I connected and tested the last version of our Power Harnessing System (PHS) circuit of [[michka:research:microbial_fuel_cells:cardiff6|our last working session in Cardiff]]. +   * Paul started up the MFCs, and performed power tests. 
-   * We saw that the energy bursts provided by the one-transistor version of the PHS circuit to the BBC microbit were quite short because of a mismatch between the nominal charge voltage of the supercap (2.7 V), the minimal power supply voltage of the BBC microbit (1.7 V), and the voltage drop across the circuit (about 1 V). +   * Paul wrote our contribution to the V&A Digital Design weekend publication. 
-   * The duration of the BBC microbit activity bursts seems to increase linearily as the capacity of the supercaps increase. +   * Michka performed tests on the Power Harnessing System (PHS) circuit. 
-   * We also observed that the two-transistor version of the PHS circuit in which the second transistor is activated by the BBC microbit itself does not seem to work, and probably never will, because it seems that the output voltage provided by the BBC microbit cannot be higher than the voltage it is supplied with.+     * The best circuit we got so far is the following one : 
 +       * the + pin of the power supply is connected to the + pin of the supercapacitor. 
 +       * the + pin of the supercapacitor is connected to the + input pin of the 1381E. 
 +       * the - pin of the supercapacitor is conneced to the ground of the power supply. 
 +       * the - input pin of the 1381E is connected to the ground of the power supply. 
 +       * the output pin of the 1381E is connected to the gate of a KSD5041QTA transistor. 
 +       * the collector of the transistor is connected to the  
 +       * the emitter of the transistor is connected to the 3V pin of the BBC microbit. 
 +       * the ground pin of the BBC microbit is connected to the ground of the power supply. 
 +     * With two 2.8 V 10F supercaps in parallel, we obtain a 56 seconds run of the blinking BBC microbit.
  
 ====Paul, July 15th==== ====Paul, July 15th====
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-      * Testing stainless-steel-scrubbers electrodes - which at least partially worked+        * The clay pots had to cook over 36 hours, the temperature gradually rising to 1200 °C. This high temperature allows for waterproofing of the pots without the use of glaze or additional treatments. 
 +      * Testing stainless-steel-scrubbers electrodes - which at least partially worked. 
 +        * Over the long term, they seem to work as well as the test battery with graphite felt electrodes.
       * Designing & prototyping the robotic system design       * Designing & prototyping the robotic system design
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          * The current structure is made of two BBC microbit modules which communicate, placed in a clay/metal structure.          * The current structure is made of two BBC microbit modules which communicate, placed in a clay/metal structure.
  
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      * The voltage drop between the + input pin voltage and the output voltage seems to be around -0.15 to -0.2 V.      * The voltage drop between the + input pin voltage and the output voltage seems to be around -0.15 to -0.2 V.
  
-===Discussion, conclusion, future work===+===Discussion & conclusion===
  
    * The current typology of the one-transistor version of the circuit does not give the BBC microbit a long autonomy because there is a mismatch between the nominal charge voltage of the supercap, the minimal power supply voltage of the BBC microbit, and the voltage drop across the circuit. Possible options to overcome these pitfalls include :    * The current typology of the one-transistor version of the circuit does not give the BBC microbit a long autonomy because there is a mismatch between the nominal charge voltage of the supercap, the minimal power supply voltage of the BBC microbit, and the voltage drop across the circuit. Possible options to overcome these pitfalls include :
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 ==Test #10 - Changing the transistors== ==Test #10 - Changing the transistors==
  
-   * Results to be transcribed from notes. +   * I tested several transistors I had on a shelf after my unfortunate joule thief experiments. 
-   * (Spoiler : the KSD5041QTA is the best transistor I have for this regard.)+   * I replaced the 2N3904 with each of them and watched how the circuit performed. 
 +     * Regarding the SS850BBN transistor: 
 +       * The voltage at the + pin of the power supply was 2.81 V. 
 +       * The voltage at the 3V pin of the BBC microbit was 1.98 V. 
 +       * The voltage at the output pin of the 1381E was 2.69 V. 
 +       * The collector-emitter voltage drop was 0.71 V. 
 +       * When running the BBC microbit on the supercap, the BBC microbit stopped to work when the voltage across the supercap reached 2.51 V, after about 16 seconds operation. 
 +     * Regarding the BC63916 transistor: 
 +       * The voltage at the + pin of the power supply was 2.81 V. 
 +       * The voltage at the output pin of the 1381E was 2.71 V. 
 +       * The voltage at the 3V pin of the BBC microbit was 1.98 V. 
 +       * The collector-emitter voltage drop was 0.73 V. 
 +     * Regarding the KSD5041QTA transistor: 
 +       * The voltage at the + pin of the power supply was 2.81 V. 
 +       * The voltage at the output pin of the 1381E was 2.75 V. 
 +       * The voltage at the 3V pin of the BBC microbit was 2.09 V. 
 +       * The collector-emitter voltage drop was 0.66 V. 
 +       * When running the BBC microbit on the supercap, the BBC microbit stopped to work when the voltage across the supercap reached 2.41 V, after about 25 seconds operation. 
 +   * **Conclusion : the KSD5041QTA is the transistor which allows the longest run time for the BBC microbit.**
  
 ==Test #11 - Switching the 1381E for 1381J== ==Test #11 - Switching the 1381E for 1381J==
  
    * The 1381J voltage detector does not trigger at 2.8 V, probably because the voltage is too low, we therefore get a 0 voltage on the 1381J output, and a 0 voltage on the BBC microbit 3V power supply pin.    * The 1381J voltage detector does not trigger at 2.8 V, probably because the voltage is too low, we therefore get a 0 voltage on the 1381J output, and a 0 voltage on the BBC microbit 3V power supply pin.
-   * Conclusion : using the 1381J does not improve the autonomy of the BBC microbit.+   * **Conclusion : using the 1381J does not improve the autonomy of the BBC microbit.**
  
 ==Test #12 - Changing the BBC microbit output mode from analog to digital== ==Test #12 - Changing the BBC microbit output mode from analog to digital==
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    * When powered through our one-transistor circuit, we obtain 1,75 V on pin 1, the same as on (analog) pin 0, input power pin 3V being powered at 1,84 V.    * When powered through our one-transistor circuit, we obtain 1,75 V on pin 1, the same as on (analog) pin 0, input power pin 3V being powered at 1,84 V.
      * We therefore cannot hope that the BBC microbit will open the gate of the second transistor controlling the line powering itself, as the gate voltage will always be a little bit lower than the emitter voltage in this version of a two-transistors circuit.      * We therefore cannot hope that the BBC microbit will open the gate of the second transistor controlling the line powering itself, as the gate voltage will always be a little bit lower than the emitter voltage in this version of a two-transistors circuit.
-   * Conclusion : using the digital output of the BBC microbit does not improve the autonomy of the BBC microbit.+   * **Conclusion : using the digital output of the BBC microbit does not improve the autonomy of the BBC microbit.**
  
 ====Michka, September 16th==== ====Michka, September 16th====
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 ==Test #13 - Changing the supercapacitors== ==Test #13 - Changing the supercapacitors==
  
-   * For some with higher nominal charge voltage - Experiment still to be performed. +   * For some with higher nominal charge voltage ? 
-   * For some with higher capacity - Experiment still to be performed.+   * For some with higher capacity ?
    * Elak needed one week delivery to provide supercaps, so experiment cancelled for now...    * Elak needed one week delivery to provide supercaps, so experiment cancelled for now...
-   * But, in the shower, a light bulb sprouted on top of my head. To increase the operation voltage of the circuit or the overall capacity, I could just pile up supercapacitors !!!+   * But, in the shower, an idea occured to me: to increase the operation voltage of the circuit or the overall capacity, I could just pile up supercapacitors !!!
    
 ==Test #14 - Piling up supercapacitors in series== ==Test #14 - Piling up supercapacitors in series==
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