Greetings,
I'm in the process of building an ESP-32 powered project that will run a HC-SR04P Sonar Sensor to measure the water level in the rain water tanks that supply our house and out-buildings. Once I get the prototype sorted out, I'll be building six of these units for use around all the rain water tanks around the house and the out-buildings.
The water tanks close to the house will use the ESP32 on-board WIFI to communicate. For the rest of the tanks located at the out-buildings, I'll still use the ESP32, but instead of WIFI, I plan to use NRF24L01 modules with external antennas, for long distance data transmission. I've done some experiments with the NRF24L01, and have been able to achieve reliable data transmission up to about 1.2 Kilometers (with line-of-sight). As the furtherest out-building is 800 meters from the house, and I can get line of sight to all of the out-buildings, these modules should be able to do the job. At that range the data transmission speed is quite slow, but then the data I'm sending from each ESP32 is just a single two digit number, plus any data and communications overhead required by the radio modules, so low communications speed won't matter. There will be a single NRF24L01 and an ESP32 located at the house to receive the comms from the NRL24L01 transmitters at each out-building, and then upload the data via the ESP32's WIFI to the MQTT Server.
I've had a WIFI prototype running for about a month so far. The ESP-32 connects to the house's WIFI, and uploads the tank's water level data to my MQTT server. The prototype is currently running on a single 18650 Li Ion Cell which takes about ten days to discharge to 3 volts. The ESP-32 and HC-SR04P both run on 3.3 volts. (Note: The HC-SR04P is a newish version of the HC-SR04 that has been modified to run on a range of voltages from 5 volts down to 3.3 volts. The original HC-SR04 is a 5 volt only device, and doesn't work well with the ESP devices, without extra level shifting circuitry and dual 5 v and 3.3v power supplies.)
The ESP-32 is in Deep Sleep all most all the time, only waking up for about a minute once every hour, to take a reading and send the reading to the MQTT Server, and then going back into Deep Sleep.
So far I haven't found a way to power down the HC-SR04 when the ESP32 is in Deep Sleep, so at the moment the Deep Sleep power consumption, at 30 mA, is not as low as I'd like to get it. The ESP32 module itself only draws about 40 micro Amps when in Deep Sleep, so if I can put the HC-SR04P to sleep as well, the potential power reduction is worth chasing. When the ESP32 wakes up, and turns it's WIFI on, and takes it's water depth readings, the total consumption varies a lot as the WIFI connects etc, but averages at about 80 mA for that one minute period each hour.
Due to the location of the water tanks, well away from the house and any mains electricity supply, I need this project to be powered by a solar panel.
Which brings me to a few design questions that I hope you might be able to help with.......
Many thanks,
Roy
I'm in the process of building an ESP-32 powered project that will run a HC-SR04P Sonar Sensor to measure the water level in the rain water tanks that supply our house and out-buildings. Once I get the prototype sorted out, I'll be building six of these units for use around all the rain water tanks around the house and the out-buildings.
The water tanks close to the house will use the ESP32 on-board WIFI to communicate. For the rest of the tanks located at the out-buildings, I'll still use the ESP32, but instead of WIFI, I plan to use NRF24L01 modules with external antennas, for long distance data transmission. I've done some experiments with the NRF24L01, and have been able to achieve reliable data transmission up to about 1.2 Kilometers (with line-of-sight). As the furtherest out-building is 800 meters from the house, and I can get line of sight to all of the out-buildings, these modules should be able to do the job. At that range the data transmission speed is quite slow, but then the data I'm sending from each ESP32 is just a single two digit number, plus any data and communications overhead required by the radio modules, so low communications speed won't matter. There will be a single NRF24L01 and an ESP32 located at the house to receive the comms from the NRL24L01 transmitters at each out-building, and then upload the data via the ESP32's WIFI to the MQTT Server.
I've had a WIFI prototype running for about a month so far. The ESP-32 connects to the house's WIFI, and uploads the tank's water level data to my MQTT server. The prototype is currently running on a single 18650 Li Ion Cell which takes about ten days to discharge to 3 volts. The ESP-32 and HC-SR04P both run on 3.3 volts. (Note: The HC-SR04P is a newish version of the HC-SR04 that has been modified to run on a range of voltages from 5 volts down to 3.3 volts. The original HC-SR04 is a 5 volt only device, and doesn't work well with the ESP devices, without extra level shifting circuitry and dual 5 v and 3.3v power supplies.)
The ESP-32 is in Deep Sleep all most all the time, only waking up for about a minute once every hour, to take a reading and send the reading to the MQTT Server, and then going back into Deep Sleep.
So far I haven't found a way to power down the HC-SR04 when the ESP32 is in Deep Sleep, so at the moment the Deep Sleep power consumption, at 30 mA, is not as low as I'd like to get it. The ESP32 module itself only draws about 40 micro Amps when in Deep Sleep, so if I can put the HC-SR04P to sleep as well, the potential power reduction is worth chasing. When the ESP32 wakes up, and turns it's WIFI on, and takes it's water depth readings, the total consumption varies a lot as the WIFI connects etc, but averages at about 80 mA for that one minute period each hour.
Due to the location of the water tanks, well away from the house and any mains electricity supply, I need this project to be powered by a solar panel.
Which brings me to a few design questions that I hope you might be able to help with.......
- Solar Panel. I've got a few 12 volt 3 watt Polycrystalline 145 mm x 145 mm solar panels left over from a previous project, so one of those will do (I hope) for the solar powered prototype. These panels have a short circuit current of about 250 mA in bright sun. In the mean time, I working on researching how to calculate solar panel size requirements ..... and battery chemistry and current draw requirements will need to feed into those requirements. I'm located in a sub-tropical area in Australia, with an abundance of sunny days throughout the year, so there should be more than enough sunlight to keep a system like this running all year round. And as we're fairly close to the Tropic of Capricorn, in mid-winter we still get 10 hours of sunlight per day, with 14 hours per day in mid Summer.
- Solar Charger Circuit. I want to keep the solar panel used in the production version of this device as small as practical, which means that the current available for battery charging will be fairly low. So, I'd like to focus on a Trickle Charger circuit that will simply keep the battery topped off. According to the Meteorological records for this area, it's rare (roughly once every three years) for us to get more than 5 days of 100% overcast in a row, so the battery needs to have enough capacity to run the system for at least five days, and as we only have a trickle charger, the battery capacity needs to be such that the remaining charge after 5 days of 100% overcast is such that the small solar panel and trickle charger will be able to top the battery's charge off again within one or two days, whilst both charging the battery and running the ESP32 and it's ancillaries..
- Battery Chemistry Choice. My understanding is that Li Ion, Li Po, and LiFePo4 cells all dislike being trickle charged (with some authors going as far as to say that it is impossible to trickle charge these Li based cells). So, I'm leaning towards using 3 NiMH cells, probably AA size, or maybe C size cells, if needed.
- There are plenty of Internet based resources for calculating Solar Panel size requirements for House Sized Solar Panel Systems, but very little that I can find for calculating Solar Panel requirements for small projects like this one. Can anyone point me to a suitable solar panel calculation resource that is relevant for a project this small ?
- Battery Chemistry. Your opinions please ? In choosing to use NiMH cells, am I going in the right direction for the right reasons ? Are there other alternatives that I should be considering ?
- Solar Trickle Charger. For a little solar panel, is it worth trying to find or design a solar charger that has MPPT functionality, or is MPPT only useful on large (i.e. house sized) Solar Panel systems ?
- Solar Trickle Charger Circuit for NiMH Cells. About forty years ago, I trained as an Electronic Technician, and then I went on to work in the Computer industry as a Programmer and a Manager for the next 35+ years. So my electronic knowledge is not current, and on top of that it's pretty rusty. However, I'm well able to build from a circuit diagram, including designing and etching the circuit board, But, designing the Solar Trickle Charger Circuit itself is beyond my skill level. So, can anyone suggest a design for a Solar Trickle Charger Circuit for NiMH Cells, that would meet these requirements ?
Many thanks,
Roy
