• Now working for 10 consecutive days

    Capt. Flatus O'Flaherty3 days ago 0 comments

    The device has been outside and working now for 10 days, transmitting regularly through the day when solar power is available and through the night after a nice sunny day. However, most days it has been cloudy and even on bright days the sun just hovers on the horizon and bluntly refuses to rise any higher. It's a great test for the system as, other than on the North Pole, this is a great test environment. The AemLION did it's job well and after taking a few measurements by hand of the battery voltage every now and again, the voltage never dropped below 3.6V and so the battery was always well protected.

    The next step is to get the battery voltage data onto an online database and start drawing online graphs. There will also be some tinkering with the transistor and gate circuit to try and see if there is any leakage current over the collectors and emitters. There's some new circuit boards arriving although currently stuck amongst Year of the Rabbit celebrations and COVID in China and I'm hoping to do some side by side tests using different design parameters and look at the graphical outputs for performance evaluation.

  • First test out in the wild

    Capt. Flatus O'Flaherty01/19/2023 at 17:56 0 comments

    This is the first outside test, with the device angled very low to the ground due to the northerly latitude and the fact that the sun just seems to hover on the horizon. Basically, the whole of December and January is pretty much useless for solar power where I live. Hopefully, the device can capture just enough photons to survive the long, cold night.

  • Gadget explanation

    Capt. Flatus O'Flaherty01/19/2023 at 17:20 5 comments

    In the latest design iteration there were a few omissions, such as a trace from the battery pad on the harvester to the battery, which is pretty crucial! Other than that, the PCB was perfect, but required a couple of ugly 1MOhm resistors to fly across from the battery +ve to ground to measure the ongoing battery voltage. The original design had the ESP32 powered by 3.5 volts through a small transistor, but this failed as the voltage dropped to 3V and so a few traces on the PCB had to be cut and some red flyer wires soldered on. The yellow flyer wire is just a 3V supply to enable the buck booster. The ESP32 is now powered by the buck booster, using the onboard 5V to 3.3V regulator. It's lucky that the buck booster was there as otherwise the board would be for land fill. The main reason for the buck booster is to power the power hungry LoRa transmitter which needs at least 5V to get a decent transmit power. 5.5 volts would be even better as then the full 1 Watt of power could be accessed.

    The general idea of this gadget is that a extremely low power timer chip keeps all the main devices strictly in the 'OFF' state by means of a couple of low leakage NPN transistors and a logic gate. Obviously, the energy harvester is also active and when the battery has a reasonable level of charge the harvester will output a steady 3.3V to the AND gate. The gate waits for the timer to send it's own 3.3V signal and when both inputs are high, it sends a 3.3V high signal to the next transistor. At this point, the main power guzzling devices are activated and, hopefully, some kind of data gets transmitted through the LoRa module. Lastly, the power guzzlers need to be turned off and this is done by simply sending a 3.3V signal to the relevant pin on the timer. All worked fine, BUT this last connection caused an unexpected problem as it turns out the timer can only be set to a maximum of 22 minutes with this configuration. After much head scratching, I realised that the connection that resets the timer must have some resistance or capacitance in it. I kind of proved this by making different connections using the resister switch bank and inferring that there's about 100K Ohms of resistance on the MCU pin. Unfortunately, the trace to the MCU is not accessible and cant be hacked as it's covered with solar panels. As a work around, I used the strangely titled 'Preferences.h' library to  save a bootCounter variable permanently into the ESP32 flash memory and count about 21 reboots of the MCU until 6 hours had elapsed. Does it work ..... Yes it does !!! Obviously, there's a small amount of energy loss every time the ESP32 boots up, but it's only on for about 0.5 seconds every 17 minutes. The main thing is that it does not waste energy trying to transmit data every 17 minutes whn a 6 hour time interval is more appropriate for an extreme low power device like this one.

    Any casual reader might well be excused for asking the question 'Why not just use the deep sleep mode on the ESP32?' Certainly, this would have been a good solution, but there are some notable advantages as below:

    • We can experiment with specialised low power timer chips to find the most frugal one. Currently using TPL5110DDCT, which consumes 35 nA, compared to the ESP32 which uses 10uA in deep sleep. This chip is, in theory, 300 times better than the ESP32, although losses in the transistors and gate need to be taken into account as well. The TC7S08F(F) gate uses 1 uA at 6V, according to the datasheet but could be turned off if the battery falls below 3.6V. No quiescent or leakage current data is available for the transistors.
    • We can experiment with low leakage transistors to find the best ones.
    • The 5V to 3.3V regulator that seems to be required for the ESP32 can be completely switched off.
    • The buck boost circuit that seems to be required to power the ESP32 can be completely disconnected.
    • The power to the Ebyte module is completely disconnected due to disconnection of the aforementioned...
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  • Upgrade to new form factor

    Capt. Flatus O'Flaherty01/19/2023 at 15:31 0 comments

    The business card sized form factor has now been abandoned, maybe even forever. The new PCBs are 73mm wide, a perfect fit for these fancy Fibox polycarbonate enclosures, but also, by sheer coincidence, the exact size of the length + width of the SM141K07 solar panels. Looking closely at the photo above, it can be seen that the panels are arranged in a four sided star pattern with a hole in the middle just big enough for the coin cell fitting - neat eh?

    During the first series of tests, the re-chargable coin cell was not used as it's pretty hard core working out where charge is or is not disappearing to with such a small capacity battery. A larger 1000 mAh is currently being used.

  • Circuit Upgrade

    Capt. Flatus O'Flaherty12/08/2022 at 18:52 0 comments

    I want to add a low current draw timer with nano amp rating as I've noticed that the device just keeps on wanting to turn on and do something 10 or 12 times in succession before it finally drains the battery too much. An adjustable timer would be very useful as long as it does not consume more than a few Nano Amps when quiescent. There's an 'AND' type logic gate which only allows the ESP32 to be ressurrected from the dead if both the timer and the energy harvester chip allow it. NPN transistors apparently have much better quiescent current levels than mosfet, in the order of x60 better, so one of these was selected for the main switch. I tried activating this NPN directly from a pin from the ESP32, but it drained current some how and wrecked the battery. Tried putting it through a diode and eventually found that another NPN transistor activating a small relay worked just fine and the battery remained fully charged all day and night. I'd really like to get rid of the relay as it draws about 30 mA, so maybe a bit more experimentation is necessary. But it works fine for now.

  • Upgrading the Device

    Capt. Flatus O'Flaherty12/06/2022 at 17:39 0 comments

  • BES components

    Capt. Flatus O'Flaherty10/23/2022 at 10:52 0 comments

    Push-fit Tank Connector - 40mm White Part number: 11121 £2.16 1 £2.16
    Push-fit Straight Coupling - 40mm White Part number: 11098 £1.43 1 £1.43
    Push-fit Screwed Access Plug - 40mm White Part number: 11125 £2.70 1 £2.70

  • RS Online Components​

    Capt. Flatus O'Flaherty10/03/2022 at 11:51 0 comments

    2 In stock - FREE next working day delivery available
    RS PRO LIR2032 Button Battery, 3.6V, 20mm Diameter RS PRO LIR2032 Button Battery, 3.6V, 20mm Diameter RS Stock No. 183-4291 Brand RS PRO RoHS status: Compliant Update | Remove £1.76 Each £3.52  
    10 In stock - FREE next working day delivery available
    TDK, 0603 (1608M) 10μF Multilayer Ceramic Capacitor MLCC 10V dc ±10% , SMD C1608X5R1A106K080AC TDK, 0603 (1608M) 10μF Multilayer Ceramic Capacitor MLCC 10V dc ±10% , SMD C1608X5R1A106K080AC RS Stock No. 788-2893 Brand TDK Mfr. Part No. C1608X5R1A106K080AC RoHS status: Compliant Update | Remove £0.267 Each (In a Pack of 10) £2.67  
    Selected packaging: Each (In a Pack of 10) Other packaging options available
      Show accessories  
    1 In stock - FREE next working day delivery available
    CHIPQUIK SMD291AX Solder Paste, 15g Syringe CHIPQUIK SMD291AX Solder Paste, 15g Syringe RS Stock No. 146-6187 Brand CHIPQUIK Mfr. Part No. SMD291AX RoHS status: Not compliant Update | Remove £12.86 Each £12.86  
    5 In stock - FREE next working day delivery available
    Panasonic 4.7Ω, 2512 (6432M) Thick Film SMD Resistor ±1% 1W - ERJ1TRQF4R7U Panasonic 4.7Ω, 2512 (6432M) Thick Film SMD Resistor ±1% 1W - ERJ1TRQF4R7U RS Stock No. 721-6328 Brand Panasonic Mfr. Part No. ERJ1TRQF4R7U RoHS status: Compliant Update ...
    Read more »

  • Other Components

    Capt. Flatus O'Flaherty09/30/2022 at 11:36 0 comments

    Adafruit TPS 61023 5.2V Power buck booster

    AEMLION Energy Harvester .... Tindie

    EBYTE E22-400M30S IPEX 1W LoRa module

    TinyPico Nano ESP32 module ... Unexpectedmaker.com

  • RS Online Components

    Capt. Flatus O'Flaherty09/30/2022 at 11:20 0 comments

    RS PRO LIR2032 Button Battery, 3.6V, 20mm Diameter RS PRO LIR2032 Button Battery, 3.6V, 20mm Diameter RS Stock No. 183-4291 Brand RS PRO