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First test out in the wild
01/19/2023 at 17:56 • 0 commentsThis 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.
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Gadget explanation
01/19/2023 at 17:20 • 5 commentsIn 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 buck booster.
- If the battery falls below 3.6V, there will never be any attempt to power on the ESP32 due to one of the inputs to the AND gate being in the LOW state, which will save energy when most needed. We cant do this using Deep Sleep mode, which would just continue to drain the battery and damage it.
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Upgrade to new form factor
01/19/2023 at 15:31 • 0 comments -
Circuit Upgrade
12/08/2022 at 18:52 • 0 commentsI 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.
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Upgrading the Device
12/06/2022 at 17:39 • 0 comments -
BES components
10/23/2022 at 10:52 • 0 commentsPush-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
10/03/2022 at 11:51 • 0 comments2 In stock - FREE next working day delivery available 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 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 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 RS Stock No. 721-6328 Brand Panasonic Mfr. Part No. ERJ1TRQF4R7U RoHS status: Compliant Update | Remove £0.70 Each (In a Pack of 5) £3.50 Selected packaging: Each (In a Pack of 5) Other packaging options available 10 In stock - FREE next working day delivery available Yageo 0Ω, 2512 (6432M) Thick Film SMD Resistor ±5% 1 W, 2 W - RC2512JK-070RL RS Stock No. 198-8545 Brand Yageo Mfr. Part No. RC2512JK-070RL RoHS status: Compliant Update | Remove £0.161 Each (On a Tape of 10) £1.61 Selected packaging: Each (On a Tape of 10) Other packaging options available 1 In stock for delivery within 1 working days when ordered before 6pm Assemtech Reed Switch Rectangular 100V, NO, 250mA RS Stock No. 289-7783 Brand Assemtech Mfr. Part No. S1365 RoHS status: Compliant Update | Remove £3.90 Each £3.90 Show accessories 1 In stock - FREE next working day delivery available Assemtech Magnet for Use with Proximity Switch RS Stock No. 289-7812 Brand Assemtech Mfr. Part No. PSM BLK RoHS status: Compliant Update | Remove £2.65 Each £2.65 Show accessories 1 Available to back order for despatch 10/11/2022 Assemtech Reed Switch Rectangular 100V, NC, 500mA RS Stock No. 361-4961 Brand Assemtech Mfr. Part No. PSB130/30 RoHS status: Compliant Update | Remove £6.79 Each £6.79 Show accessories -
Other Components
09/30/2022 at 11:36 • 0 commentsAdafruit TPS 61023 5.2V Power buck booster
AEMLION Energy Harvester .... Tindie
EBYTE E22-400M30S IPEX 1W LoRa module
TinyPico Nano ESP32 module ... Unexpectedmaker.com
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RS Online Components
09/30/2022 at 11:20 • 0 commentsRS PRO LIR2032 Button Battery, 3.6V, 20mm Diameter RS Stock No. 183-4291 Brand RS PRO -
Digikey Components
09/30/2022 at 11:11 • 0 comments1 BU2032SM-JJ-MINI-GCT-ND BU2032SM-JJ-MINI-GTR MPD (Memory Protection Devices) BATT HOLDER COIN 20MM 1 CELL SMD Immediate 1.27000 £2.54 2 563-1102-1-ND CUS-12TB Nidec Copal Electronics SWITCH SLIDE SPDT 300MA 4V Immediate 0.66000 £1.32 3 2994-SM141K07L-ND SM141K07L ANYSOLAR Ltd MONOCRYST SOLAR CELL 215MW 4.84V Immediate 6.36000 £12.72 4 455-2567-1-ND UB-MC5BR3-M404-4S-TB NMP JST Sales America Inc. CONN RCPT MICRO USB B 5POS SMD Immediate 0.95000 £1.90 5 DS18B20+-ND DS18B20+ Analog Devices Inc./Maxim Integrated SENSOR DIGITAL -55C-125C TO92-3 Immediate 8.07000 £8.07 6 RNCP0603FTD1K00CT-ND RNCP0603FTD1K00 Stackpole Electronics Inc RES 1K OHM 1% 1/8W 0603 Immediate 0.09000 £0.45 7 1497-1117-1-ND XZCBD53W-8 SunLED LED BLUE CLEAR CHIP SMD Immediate 0.49000 £2.45 8 1497-1132-1-ND XZDGK53W-1 SunLED LED GREEN CLEAR CHIP SMD Immediate 0.53000 £2.65 9 1276-1935-1-ND CL10B104KB8NNWC Samsung Electro-Mechanics CAP CER 0.1UF 50V X7R 0603 Immediate 0.09000 £0.45 10 311-4.70KHRCT-ND RC0603FR-074K7L YAGEO RES 4.7K OHM 1% 1/10W 0603 Immediate 0.09000 £0.45 11 311-2.00KHRCT-ND RC0603FR-072KL YAGEO RES 2K OHM 1% 1/10W 0603 Immediate 0.09000 £0.45 12 311-0.0LECT-ND AC0603JR-070RL YAGEO RES SMD 0 OHM JUMPER 1/10W 0603 Immediate 0.09000 £0.45