2d:T63b,md` which is a modular, stackable IOT development platform (with an edge lenght of 5cm), based on the ESP32-Chip. It offers WiFi, bluetooth, 3 button, an sdcard slot, a 1W speaker and microphone, a hall sensor, and a bottom shield with a small battery and a lot input and output connectors to which we can directly connect sensors. The device can be programmed in C++, with [UIFlow](https://m5stack.com/pages/uiflow) or the [Arduino environment](arduino.cc). The m5stack comes with an addon for Arduino that allows you to use all builtin hardware and to reprogram the device via USB. The UI comes for Mac, Windows and Linux. We use the Arduino software to program the m5stack with [uLisp](http://www.ulisp.com/). uLisp is written in C++ that can be easily compiled with the Arduino software. The high-level software can thus be written in high-level uLisp which allows for interative programming and updating via USB or even WiFi. uLisp itself can be easily modified in C++ and thus make the hardware of the m5stack available as lisp functions to the high-level uLisp sortware. Like this we can give uLisp access to sensors, control the WiFi and use HTTP calls to put data directly into Dydra. ### demo This has been demonstrated with a working prototype in December already, with a demo that would have the m5stack connect to a WiFi, get the current time via NTP and put a statement into Dydra at https://de8.dydra.com/max/test/service that a button has been pressed at a certain time: \`\`\`text "2020-12-02T00:24:40" . \`\`\` `2e:T67b,temp_sensor = md`### temperatur sensor [Waterproof DS18B20 Digital Temperature Sensor for Arduino from DFRobot](https://www.dfrobot.com/product-689.html) (Bought at Amazon: [DFRobot Waterproof DS18B20 Digital temperature sensor](https://www.amazon.de/dp/B01B0IO6S2/ref=cm_sw_r_cp_apa_fabc_s0LVFbVWB2B0P?_encoding=UTF8&psc=1).) More documentation in DFRobot's wiki: [Waterproof DS18B20 Digital Temperature Sensor, SKU: DFR0198](https://wiki.dfrobot.com/Waterproof_DS18B20_Digital_Temperature_Sensor__SKU_DFR0198_). [Datasheet for DS18B20](https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf) #### Buy list: - a single 4.7k Ω Resistor - <10 cent/piece but shops are closed, online e.g. at Amazon [20 pieces for 1,27 EUR + 2,20 EUR shipping](https://www.amazon.de/Widerstand-St%C3%BCck-Metallschicht-Metallfilm-Widerst%C3%A4nde/dp/B00I8NOOEY) - or: [Gravity: Terminal Sensor Adapter V2.0 from DFRobot](https://www.dfrobot.com/product-203.html), SKU: DFR0055 - More documentation in DFRobot's wiki: [Terminal sensor adapter V2, SKU: DFR0055](https://wiki.dfrobot.com/Terminal_sensor_adapter_V2_SKU_DFR0055) - costs: <3 EUR but seems to be hard to get in Germany Update: I found a bunch of 10k Ω at home. That should work. It is just for the pull-up. (It will use less power than the specified 4.7k Ω, but if need be I can put to 10k Ω in parallel to get 5k Ω.) Two 10k Ω resisters were necessary to talk to the digital temperature sensor. Note: The sensor uses the 1-Wire protocol, that is, multiple sensors can be attached to the same pin of the esp32. We could attach dozens or even hundreds of temperature sensors not waisting more pins. `2f:T9e8,ph_sensor = md`### pH sensor [Gravity: Analog pH Sensor/Meter Kit V2 from DFRobot](https://www.dfrobot.com/product-1782.html) (Bought at Amazon: [Gravity: Analoge pH-Sensor/Messgerät-Kit V2 ](https://www.amazon.de/dp/B07L2RSHYN/ref=cm_sw_r_cp_apa_fabc_7ZLVFbYGQYXCG?_encoding=UTF8&psc=1).) More documentation in DFRobot's wiki: [Gravity: Analog pH Sensor/Meter Kit V2, SKU: SEN0161-V2](https://wiki.dfrobot.com/Gravity__Analog_pH_Sensor_Meter_Kit_V2_SKU_SEN0161-V2). The sensor comes with a board and can be uses as is. Very long story, but here the gist of it: these sensors are fragile and not easy to handle, we have not the best sensor, the software is crappy but we will get some values. I propose to have the IOT device to output the measured analoge voltage directly and not try to compute any pH value itself. It might also be done by a Dydra view. We would want to store reference voltages from sensor calibration as well to be able to monitor sensor deterioration as well which is quite relevant for this kind of sensor, especially for beverages that contain bigger moving particles in them. You can only derive the pH value when taking the calibration reference voltages into account, possibly having to also consider the temperatures measured by the separate temperature sensor. So we also store the temperature at the time of measurement near the probe, althought in general the temperature might be taken in different intervals than the pH level. #### Buy list: - storage solution "3NKCL" or "3N KCL" or "3M KCL" also called "3mol/L KCL". (More details, for example at: [pH Electrode Storage Solution](https://h2osync.com/product/ph-electrode-storage-solution/) or [Wikipedia on Kaliumchlorid, quoting A. F. Holleman, E. Wiberg, N. Wiberg: Lehrbuch der Anorganischen Chemie, 102. Auflage. Walter de Gruyter, Berlin 2007.](https://de.wikipedia.org/wiki/Kaliumchlorid#Verwendung).) - can be bought cheaply at [Garnelen-Guemmer for 2,59 €/100 ml + 4,90 € shipping](https://www.garnelen-guemmer.de/kcl-3mol/l-loesung-100-ml-kaliumchlorid?) or [4,99 €/250 ml](https://www.garnelen-guemmer.de/kcl-3mol/l-loesung-250-ml-kaliumchlorid) - distilled water (for cleaning to avoid cross-contamination of storage solution, referance "buffer" solutions, and, most importantly, the Kombucha and tea) - tissues (for wiping of the destilled water, to avoid delution and contamination) - later: deionized water (see also [Deionization vs. Distilled Water](https://www.uswatersystems.com/deionized-water-vs-distilled-water).) `30:T508c,md` #### How the pH sensor works ⇒ Here is a good explanation how this type of sensor works in general: [Laboratory sensors: The pH Measurement by Chromservis, Prague, CZ](https://www.chromservis.eu/c/ph-measurement?lang=EN). ⇐ More in depth explanations with a lot of images: [pH Theory Guide: A Guide to pH Measurement – the Theory and Practice of pH Application by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf). (Found via https://chemistry.stackexchange.com/questions/34878/solution-for-storing-a-glass-electrode, noted here as that pages contains more useful information about the KCL solutions.) (Different version: [pH Theory Guide: A Guide to pH Measurement – the theory and practice of laboratory pH applications, Practical description of how to measure pH by Mettler-Toledo AG Process Analytics](https://www.mt.com/de/en/home/library/tips-and-tricks/lab-analytical-instruments/Guide_pH_meas/jcr:content/download/file/file.res/51300047_pH-Guide_E.pdf).) #### software library of the DFRobot sensor long story short: We will not use that library but have to do calculations ourselves. details: The DFRobot sensor comes with a "Software library supports two-point calibration and automatically identifies standard buffer solution": [DFRobot_PH Library, Github](https://github.com/DFRobot/DFRobot_PH). It has a function "calibration", and a function "readPH" that takes a voltage and a temperatur as input and returns the calculated pH level, its documentation reads "Convert voltage to PH with temperature compensation" and "In order to guarantee precision, a temperature sensor such as DS18B20 is needed, to execute automatic temperature compensation.", and the included examples says "read your temperature sensor to execute temperature compensation" but this is **a blatant lie** as the implementation in [DFRobot_PH.cpp](https://github.com/DFRobot/DFRobot_PH/blob/master/DFRobot_PH.cpp) does not use that temperature value at all for the calculation! #### pH when brewing Kombucha "Kombucha pH level is very important when brewing, while simple, there are easy rules to follow to know that your kombucha’s pH level is where it needs to be. The starting pH of kombucha needs to be at or under 4.5. As your kombucha ferments, the pH will drop while the different bacteria create acetic and gluconic acid and lower the pH. Finished kombucha is based on taste with a pH range between 2.5 and 3.5. So if you like it sweet, you should aim for a higher pH at 3.5. If you like your kombucha tart, you should let it ferment longer while tasting daily until you are happy with the tartness of your brew but keeping it above 2.5 pH." (from [Why is pH important for brewing Kombucha? by Fermentaholics](https://fermentaholics.com/why-is-ph-important-for-kombucha/)) pH range to be measured: "The Kombucha fermets should always be below pH 4.5, and the finished kombucha should have a pH range between 2.5 and 3.5 (from [Why is pH important for brewing Kombucha? by Fermentaholics](https://fermentaholics.com/why-is-ph-important-for-kombucha/)). #### Using the pH sensor Measuring is complex and a lot of things have to be observed. Important excerpts of the specification that affect usage (from DFRobot's wiki: [Gravity: Analog pH Sensor/Meter Kit V2, SKU: SEN0161-V2](https://wiki.dfrobot.com/Gravity__Analog_pH_Sensor_Meter_Kit_V2_SKU_SEN0161-V2)): - Probe Life: >0.5 year (depending on frequency of use) - Response Time: <2min - Temperature Range: 5~60°C - Detection Range: 0~14 - Max: "pH 0-x" is most probably a lie, as "Measurement of pH below about 2.5 (ca. 0.003 mol dm−3 acid) and above about 10.5 (ca. 0.0003 mol dm−3 alkaline) requires special procedures because, when using the glass electrode, the Nernst law breaks down under those conditions" (from [Extremes of pH by Wikipedia](https://en.wikipedia.org/wiki/PH#Extremes_of_pH), but 2.5-x would be good enough. #### handling: connectors and signal conversion board and general handling - The BNC connector and the signal conversion board must be kept dry and clean, otherwise, it will affect the input impedance, resulting in an inaccurate measurement. If it is damp, it needs to be dried. - The signal conversion board cannot be directly placed on a wet or semiconductor surface, otherwise it will affect the input impedance, resulting in the inaccurate measurement. It is recommended to use the nylon pillar to fix the signal conversion board and allow a certain distance between the signal conversion board and the attached surface. - The sensitive glass bubble in the head of the pH probe should avoid touching with any hard material. Any damage or scratches will cause the electrode to fail. - After completing the measurement, disconnect the pH probe from the signal conversion board. The pH probe should not be connected to the signal conversion board without the power supply for a long time. - Before measuring another solution, be sure to wash the probe and absorb residual water-drops with paper to prevent cross-contamination between solutions. The probe can be washed with distilled water. #### handling: sensor head - The sensor head is a glass bubble which is highly fargile and needs to be kept clean. The glass bubble in the head of the pH probe (in the plastic protection grid) shall not come in contact with the hard objects, and any breakage or rubbing will invalidate the probe. - The sensor head has to be stored in its protective cap that has to be filled in a storage solution at all time. The storarge solution is "3NKCL" also called "3mol/L KCL". - When the probe is used for the first time or used for some time, the probe needs to be immersed in the 3NKCL solution for 8 hours. - When the measurement is finished, the protective cap should be put on, and a small amount of 3mol/L KCL solution should be put inside the protective cap to keep the glass bulb moist. - The plug of the pH probe must be kept clean and dry, absolutely prevent the output ends short-circuit, otherwise, it will result in inaccurate measurement or probe failure. - The probe should avoid long-term immersion in distilled water, protein, acid fluoride solution, and prevent contact with silicone oil. See also: [Maintenance and storage of pH electrodes by Chromservis, Prague, CZ](https://www.chromservis.eu/c/ph-electrode-maintenance), excerpt: "When the pH electrode is not used for a period of time, always keep it moist. Store the pH electrode in storage solution or in a pH 7 buffer. DO NOT store the electrode in distilled or deionised water as this will cause ions to leach out of the glass bulb and reference eledtrolyte, causing slow and sluggish response." #### maintenance: sensor head after long-time use - After long-term use, if you found that the percentage of the theoretical slope of the probe (PTS) slightly reduced, you can soak the lower end of the probe in 4%HF (hydrofluoric acid) for 3-5 seconds, wash with distilled water, and then soak in the 0.1MOL/L HCL solution for a few hours, rinse clean with deionized water. - ⇒ Max: This procedure has to be done to restore the probes after long-term use to ensure that the slope of the probe is good again, that is the difference in measured voltage compared to difference in pH level. - The probes are passivated by the presence of contamination-sensitive bulbs in the solution under testing conditions or by plugging the liquid boundary. The phenomenon is that the theoretical slope (PTS) is reduced, the response time is long and the readings are unstable. Therefore, according to the nature of the contaminants, they should be cleaned with an appropriate solution to make them fresh. - ⇒ Max: This means that the bulbs can change because of the solution under test (the tea) in general, but also that the probe can be blocked by bigger particles of our bacteria of the Kombucha. It seems to be a bad idea to just put the probe directly into the vessle. Do we need to filter a probe first? Can we do this by putting a filter around the probe? Still we need to make sure that the filter itself does not block and the fluid that we actually measure has the same pH level as the tea that we want to actually measure. - Attention should be paid to the selection of the cleaning agent. The soluble polycarbonate cleaning liquid, such as carbon tetrachloride, trichloroethylene, four furans and so on, may stained glass ball bubble surface, and make the probe failure, please use these with great caution! - ⇒ Max: No idea. Is this normal cleaning, long-time cleaning? Something in between? There is the washing when switching probing solution with distilled water, and the cleaning with deionized water in the procedure after long-term use (see above), but when is this "cleaning agent" supposed to be used? Here are the cleaning instruction by a manufacturer of professional labor-grade pH probes (it seems): [Hints and tips: Electrode cleaning by Chromservis, Prague, CZ](https://www.chromservis.eu/c/electrode-cleaning?lang=EN). #### calibration fluids / buffer solutions - the buffer solutions decay over time - DFRobot writes: "When calibrating, fresh standard buffer solution is recommended." (from [DFRobot Wiki](https://wiki.dfrobot.com)) - Chromservis on this: "But buffer values can change over time and so can your results. A complete range of patented buffer solutions provides never before achieved pH stability. Hamilton guarantees DURACAL pH buffers for 5 years after the date of manufacture. The pH 9.21 and pH 10.01 buffers are even stable in air." (from [Traceability by Chromservis, Prague, CZ](https://www.chromservis.eu/c/buffers-traceability)) ⇒ Max: I'd guess we can use a bottle of buffer fluid for some weeks or even months but need to make sure they are properly sealed and there is no cross-contamination (see notes above). #### calibration - on frequency: "The calibration interval is determined by the frequency of use. Normally, you can calibrate it once a month. If used frequently, it can be calibrated once a week. When calibrating, fresh standard buffer solution is recommended." (from [DFRobot Wiki](https://wiki.dfrobot.com/Gravity__Analog_pH_Sensor_Meter_Kit_V2_SKU_SEN0161-V2)) - side conclusion: the buffer solutions decay over time, see below - again on frequency: "It makes little sense to make general statements regarding the calibration frequency. Therefore, when working with unknown solutions it is advisable to repeat the calibration often in the beginning. When the calibration values are stable, the calibration frequency may be extended. In general the calibration frequency depends on the desired accuracy. To be able to calibrate during the process, an electrode in a retractable housing is very useful." (from: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 31.) - on calculation an linearity: "Most pH electrodes have a nearly linear behavior in the measuring range of pH 0 to 14. Taking advantage of this behavior a pH electrode is calibrated between two different well known pH values, for example pH 4.01 and 7.00. Between those two values a linear extrapolation and also a linear interpolation is conducted." (from [pH measurement by Chromservis, Prague, CZ](https://www.chromservis.eu/c/ph-measurement?lang=EN).) - on temperature compensation: "Automatic temperature compensation is generally used in industry, except when both calibration and pH measurement occur at a constant temperature (see […]). If the process temperature does not differ from room temperature by more than 10 °C, temperature compensation is often not necessary, since the measuring error is less than 0.15 pH units (between pH 3 and 11; see […])." (from: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 27, section "Temperature compensation".) - "It should be noted that the two buffer solutions must have a difference in pH values of at least two pH units." (from: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 30.) - "As already mentioned, the pH value is temperature dependent. Therefore, it is important that the temperature curve of the buffer is known. Additionally, the buffer and the electrode must be at the same temperature, or you must wait for the temperature to reach equilibrium." (from: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 30.) - the second buffer solution used for the slope calibration whouls have "a pH value close to the measuring value" (from: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 30.) - "The response time of the electrode can also be affected if the temperature changes between or during measurements. […] In order for a combination electrode to react rapidly to the temperature changes in the sample, the temperature of the inner pH electrode and the outer reference electrode must always be identical." (from: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 87.) - ⇒ Max: The sensor needs to be long enough in the fluid under test so that the whole sensor including the inner reference fluid reaches the same temperature. #### calculation of pH from measured voltage and temperature compensation (Note: This section is me, Max, putting the stuff of the previous section together…) The sensor gives an analoge voltage value which is read by an analog input pin of the m5stack. The voltage relates to pH level. You calibrate by submerging the probe in a pH 7 solution to determine the neutral point of the probe. Then you submerge it (after cleaning, etc.) in the pH 4 solution to get a second point in order to determine the slope of the supposed straight line. With knowledge of those two reference voltage, other voltages can be calculated by linear interpolation and extrapolation. (Another explanation with graphs in: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 84, section 5.5 Calibration / adjustment of the pH measurement setup.) (It might be a good idea to repeat the pH 4 measurement once more after the slope calculation, "if a very accurate measurement is required" (from:from: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 30.)) The sensor is assumed to be linear but this is true only at 25°C. "For an ideal sensor the theoretical slope is 59.16 mV/pH at 25ºC. Slope can be entered in mV/pH or a percentage of the theoretical slope (100% corresponds to 59.16 mV/pH)." (from [a user guide of a pH analyzer, secion 5-5. Calibration settings](https://www.manualsdir.com/manuals/360170/yokogawa-exaxt-ph450-4-wire-analyzer-for-ph-and-orp.html?page=34). This is the "Theoretical slope of the probe (PTS)" mentioned earlier in the sensor head maintenance section. So you can determine the age and deterioration of the pH sensor by relating the difference in voltage for a known pH level difference! Certainly, an information that might be useful to store for analyzation, even though we might not need to actually do temperature compensation. I am not sure about temperature compensation, yet. It is not just the sensor that is dependent on the temperature, it is actually acidity that changes with temperature, as pH is based on the activity of the H+ ion ("pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity") which seems to change with temperature (activity = movement?). (Actually, temperature has an influence on both the electrode and the sample (from: [pH Theory Guide […] by Mettler-Toledo AG Process Analytics](https://www.mt.com/dam/non-indexed/po/pro/Brochures/IB_pH_Theory_Guide_EN_230113.pdf), page 85.) And the Nernst equation that describes the relation to measured potential used by the sensor is linear dependent on the temperature. I gather from this that: if you calibrate at a certaint temperature, you can calculate pH for measurements at that temperature. But as the measured potential is dependent on the temperature, you will not be able to make sense of measurements at a different temperature. Still, we need to know the pH of the buffer solution *at that temperature*. As long as we keep more or less constant room temperature and shade the brew from sun light, we might be good. But if we do not control it enough we might need to compensate for temperature changes. As we probably keep temperature in the range of 18°C-28°C we might be good. Or do we actually brew at a higher temperature, Ivan? I read it is at least 20°C, and up to 30°C. Here is an error chart of pH vs. temperature (from: https://sensorex.com/blog/2016/05/09/ph-sensor-calibration/): ${html`

`} If that is applicable, we would have an error of less then maybe ~0.12 pH in that range (which fits to the 0.15 pH mentioned earlier). (So, if I give you a pH level with more then one digit after the point you know I am lying.) We can compare to measurements of pH test strips only to be sure we are roubly in the right range; but there are inaccurate, at best, they let you differentiate between 2.5, 3 and 3.5 (see [pH test strips for Kombucha fermenting](https://fermentaholics.com/product/kombucha-instant-read-ph-test-strips/)). Ivan notes, that we want to keep the Kambucha between 20°C and 30°C but in Winter and Summer it might be down to 15°C (and maybe up to 35°C, I guess). Ivan also wants to aim for 2 digits accuracy after the point. Update: The current signal conversion board has a Measurement Accuracy of just ±0.1@25℃, and the sensor an unspecified one. We don't get better than that. So no bother for temperature correction for that sensor+device. There is actually a "pro version" of the v2 kit: [Gravity: Analog pH Sensor / Meter Pro Kit V2](https://www.dfrobot.com/product-2069.html). Here both. sensor and board, have an accuracy of ±0.1pH (25 ℃) and the sensor is specified for 24/7 use with a Response Time of 10sec. The sensor is available separately: [Industrial pH Electrode - Armor Casing](https://www.dfrobot.com/product-1074.html), though in general I have to say I don't trust them too much anymore after the invalid information about their software… I propose we ignore the temperature error for now when calculating pH, but we store raw voltage and temperature always. At least the temperature helps as to specify the error margin, validate that the slope is close to the theoretic ideal, and later we might actually do temperature compensation if we need more accuracy. #### open questions - I am not sure if the probes are suitable for long time measurements. Maybe they are, maybe not. - The kombucha fermets should always be below pH 4.5, and the finished kombucha should have a pH range between 2.5 and 3.5 (from [Why is pH important for brewing Kombucha? by Fermentaholics](https://fermentaholics.com/why-is-ph-important-for-kombucha/)). This is a bit more away from the 7 pH that would be bad for storage of the probe and is more in the range of the 3pH (if I understand it correctly) of the 3NKCL storage solution. Maybe that means that at least should not increase the rate of deterioration of the sensor by much. - Certainly, we cannot just directly put the probe in the vessel (as the bigger particles might block the pH sensor) but I hope that it does not have to be a complicated manual lab procedure of taking a particular probe each time. It would be good to have something that measures pH automatically without human intervention. - Here are some probes that are suitable for "beverages": Ge-151 and GE-125 by [Greisinger, Remscheid Germany](www.greisinger.de) according to [GExxx_EN.pdf](https://www.greisinger.de/files/upload/en/produkte/bda/GExxx_EN.pdf). In the 100-200 Euro range. … `31:[{"id":"b29b541613f255c371a46852df23476e330b951d4c3249d1b52cc51652fc0c29a16a7059276d5cfb1cd0944dc5ebd844e495d691990a0e3ea95dbde26f485352","href":"https://static.observableusercontent.com/files/b29b541613f255c371a46852df23476e330b951d4c3249d1b52cc51652fc0c29a16a7059276d5cfb1cd0944dc5ebd844e495d691990a0e3ea95dbde26f485352","name":"2021-01-08-204855_429x294_scrot.png","type":"image/png","lastModified":1622821816941,"size":31767},{"id":"80e52a30d236b82d0573996b635ba7482113a389aadfddd659f066d6659ee2cad82b8376beadc17b8c020927493cf15dc99421bce6659ae56fd9c9ce35f1c8b9","href":"https://static.observableusercontent.com/files/80e52a30d236b82d0573996b635ba7482113a389aadfddd659f066d6659ee2cad82b8376beadc17b8c020927493cf15dc99421bce6659ae56fd9c9ce35f1c8b9","name":"M5Stack-Official-Stock-Offer-ESP32-Basic-Core-Development-Kit-Extensible-Micro-Control-Wifi-BLE-IoT-Prototype.jpg_q50.jpg","type":"image/jpeg","lastModified":1622821816941,"size":44820},{"id":"042ad9d6ef81c0bc803d2faa0d3e72986f2e84bd7f895c6a6b6a923c62289f2acbcb46ae769a242479e04079c5491cb62c8efde169d4c1a4b000715cef52f206","href":"https://static.observableusercontent.com/files/042ad9d6ef81c0bc803d2faa0d3e72986f2e84bd7f895c6a6b6a923c62289f2acbcb46ae769a242479e04079c5491cb62c8efde169d4c1a4b000715cef52f206","name":"DSC_1190s_M5Stack-Temp-pH.jpg","type":"image/jpeg","lastModified":1622821816941,"size":183521},{"id":"c8cfc8aed56907c431b7f6a060c1ffb3e060a5d0835291cf4c20da991f786f17919df10e5056a2fc3e2f90bc941c50bdf19e3c88ed94c73c515b45320e6da830","href":"https://static.observableusercontent.com/files/c8cfc8aed56907c431b7f6a060c1ffb3e060a5d0835291cf4c20da991f786f17919df10e5056a2fc3e2f90bc941c50bdf19e3c88ed94c73c515b45320e6da830","name":"DSC_1187s_M5Stack-Temp.jpg","type":"image/jpeg","lastModified":1622821816941,"size":200384}] 2c:{"title":"Dydra IOT device / sensor data source","cells":[{"id":0,"value":"md`# Dydra IOT device / sensor data source`","pinned":false,"hidden":false,"mode":"ojs"},{"id":150,"value":"md`## General information\n\nThe first prototype is using an M5Stack Basic:`","pinned":false,"hidden":false,"mode":"ojs"},{"id":107,"value":"html`\n

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First test of temperatur sensor):

\n`","pinned":false,"hidden":false,"mode":"ojs"},{"id":209,"value":"$2f","pinned":false,"hidden":false,"mode":"ojs"},{"id":408,"value":"html`\n

First test of pH sensor (temp sensor also connected):

\n`","pinned":false,"hidden":false,"mode":"ojs"},{"id":427,"value":"md`### Buy list to make a less fragile version (and have a bit extra parts):\n\\`\\`\\`text\n8x\n8 Pin Dupontkabel 2.54mm Buchse-Buchse 20 cm\nArtikel-Nr.: RBS12407\n0,72 €\nhttps://www.roboter-bausatz.de/2468/8-pin-dupontkabel-2.54mm-buchse-buchse-20-cm\n\n5x\n7 Pin Dupontkabel 2.54mm Buchse-Buchse 20 cm \nArtikel-Nr.: RBS12613\n0,26 €\nhttps://www.roboter-bausatz.de/2674/7-pin-dupontkabel-2.54mm-buchse-buchse-20-cm\n\n1x\n10x 40 Pin 2,54 mm Stiftleiste einreihig\nArtikel-Nr.: RBS10528 \n0,95 €\nhttps://www.roboter-bausatz.de/582/10x-40-pin-2-54-mm-stiftleiste-einreihig\n\n5x\nDoppelseitige Lochrasterplatine 5 x 7 cm\nArtikel-Nr.: RBS11010\n0,65 €\nhttps://www.roboter-bausatz.de/1066/doppelseitige-lochrasterplatine-5-x-7-cm\n\n5x\nDoppelseitige Lochrasterplatine 4 x 6 cm\nArtikel-Nr.: RBS11011\n0,85 €\nhttps://www.roboter-bausatz.de/1067/doppelseitige-lochrasterplatine-4-x-6-cm\n\nTotal: 15.51 € + 2.99 € shipping = 18.50 €\n\\`\\`\\`\n`","pinned":false,"hidden":false,"mode":"ojs"},{"id":402,"value":"$30","pinned":false,"hidden":false,"mode":"ojs"}],"files":"$W31","stdlib":"1","titling":"auto"}