Project Design Breakdown

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2:29

Environmental Exposure Risk Meter – Detailed Design Review 1. Project Purpose
A hand-held, solar-assisted environmental exposure meter that:
  • Measures indoor / outdoor air quality (CO₂) and ultraviolet (UV) index.
  • Connects to Wi-Fi / Bluetooth via the on-board ESP32 to push data to mobile or cloud dashboards.
  • Runs from a small Li-ion battery that can be charged by a photovoltaic (PV) panel and boosted to power-hungry peripherals when needed.
Typical use-cases: personal health monitoring, classroom air-quality indication, building-HVAC feedback, wearable sun-exposure tracking.
2. Core Hardware Blocks & Interaction 
Diagram



  
    
  
  
    
  














VBAT

3.0-4.2 V

5 V BOOST

3.3 V

UART

I²C










"Solar Panel"
"CN3791 MPPT Charger(SL2)"
"Li-ion Cell (VBAT)"
"MT3608 BoostConverter (SL1)"
"AP2112 LDO 3.3 V(U1)"
"ESP32-WROOM-32E(U2)"
"MH-Z19 CO₂ Sensor(UART)"
"VEML6075 UV Sensor(I²C)"
"LED + Two Push-Buttons(LED1, SW1, SW2)"
"Headers & JST Qwiic(J1-J6)"

Block-by-Block

BlockKey Parts (linked)FunctionNotable Design Choices / Trade-offs
PV ChargingSL2, +V_SOLAR, J4MPPT charger maximises solar harvest while safely charging Li-ion.CN3791 offers >90 % PV utilisation but needs good layout for thermal dissipation.
Battery RailVBAT, J51-cell Li-ion removable.Directly feeds LDO and boost; no ideal-diode ORing, so reverse-polarity protection is absent.
Boost ConverterSL1, VBOOST, BOOST_ENSteps 3-4 V up to ~5 V for sensors needing higher V or USB-UART flashing.MT3608 is easy to source, but >1 MHz switching may radiate – careful PCB plane design needed.
3.3 V LDOU1, C2Quiet 600 mA rail for ESP32 and logic.LDO wastes power at high Vin (boost active). Could be bypassed by feeding ESP32 directly from battery for better efficiency.
MCU / CommsU2Wi-Fi, BLE, I²C, UART, ADC; central data processing.Module avoids RF layout complexities, eases certification, but fixes antenna position constraints.
Level-Shift & AutoprogramQ2, Q3, R3, R4MOSFETs form the classic RTS/DTR auto-reset circuit for USB-UART programming & IO0 boot mode.Resistor values 10 kΩ are standard; ensure gate actually reaches 3.3 V for reliable switching.
User InterfaceLED1, R1, SW1, SW2Basic status LED and two tactile buttons.LED current set to ~3 mA (1 kΩ) – power-friendly.
Sensor InterfacesNotes reference: MH-Z19 CO₂ (UART) and VEML6075 UV (I²C) modules. Connect through headers/JST.Modular sensors allow swaps / upgrades.UART vs I²C split reduces bus loading, simplifies software.
ConnectorsJ1–J6, QwiicExternal access for sensors, programming, power.PH series provides locking, but thru-hole raises board height; could switch to SMT to save assembly time.
3. Step-by-Step Operation
  1. Energy Harvesting & Storage
    • PV panel feeds CN3791 → tracks max power point, charges Li-ion at up to 2 A (config-dependent).
    • Battery voltage (VBAT) available even without sunlight.
  2. Power-Up Sequence
    • VBAT enters U1 → stable 3.3 V rail for logic.
    • If firmware asserts BOOST_EN, MT3608 turns on, creating 5 V (VBOOST) for high-current sensors or external peripherals.
  3. Boot & Programming
    • RTS/DTR from USB-UART header (J6) toggle Q2/Q3 to pull ESP32 EN and IO0, enabling auto-flash.
  4. Sensor Polling
    • ESP32 I²C pins (IO22/IO21) communicate with VEML6075 via Qwiic connector (J3).
    • UART0 secondary (IO16/IO17 via J1 & J2) exchanges data with MH-Z19 CO₂ module.
  5. Data Processing & Transmission
    • ESP32 calculates UV index & CO₂ ppm, assesses risk, lights LED1 or pushes notifications over Wi-Fi/BLE.
  6. Low-Power Mode
    • Boost disabled, peripherals off, ESP32 in deep-sleep (~10 µA). AP2112 quiescent is ~55 µA, still the dominant drain.
4. Key Technologies & Dependencies
  • 2.4 GHz Wi-Fi/BLE stack (ESP-IDF or Arduino-ESP32).
  • I²C & UART drivers for sensor modules.
  • MPPT charging firmware optional (CN3791 is HW-only).
  • Power-budget analytics to balance sample interval vs battery.

5. Challenges & Performance Considerations

AreaRisk / ChallengeMitigation
Power EfficiencyDual regulation (boost → LDO) wastes ~30-40 % under certain loads.Feed ESP32 directly from battery (3.0-3.6 V safe) or swap boost for buck-boost.
RF InterferenceMT3608 1.2 MHz switch node near ESP antenna degrades RSSI.Place boost far from module, shield in ground pour, keep FB loop short.
ThermalCN3791 in TO-252 or QFN must dissipate up to 3 W.Large copper plane on bottom, thermal vias.
I²C Pull-upsNone present on SCL/SDA nets; bus may float.Add 4.7 kΩ to 3.3 V near connector.
DecouplingOnly two 1 µF caps shown; ESP32 spec calls for multiple 0.1 µF close to VDD & VDD3P3.Add at least 3 × 0.1 µF + 10 µF bulk near module.
DRC ErrorsCurrent design shows “Overlapping Copper”, “Floating Copper”, “Airwires”. Must be fixed before fab.Re-run layout, clear errors.
6. Opportunities for Improvement & Future Enhancements
  1. Electrical
    • Add reverse-polarity & input surge protection (Schottky + TVS).
    • Replace discrete level-shift with dedicated USB-to-UART (e.g., CP2102N) for simplicity.
    • Integrate charging fuel-gauge IC for accurate battery state-of-charge.
  2. Power Architecture
    • Adopt single buck-boost PMIC (e.g., TPS63070) to generate 3.3 V directly from 2.5-5.5 V, eliminating LDO + boost.
    • Use deep-sleep wake via RTC timer or UV/CO₂ threshold interrupts to extend battery life >1 week.
  3. Sensing & UI
    • Add temperature/humidity (SHTC3) and particulate matter (PMS5003) for full AQI.
    • Provide small e-Paper display for always-on exposure index.
  4. Firmware & Cloud
    • MQTT/HTTPS push to open-source air-quality networks (e.g., Ambient Weather, ThingSpeak).
    • BLE beacon mode for smartphone dashboards without network.
  5. Mechanical / Production
    • Conformal-coat for outdoor use.
    • Custom enclosure with integrated solar cell window and light guide for status LED.
  6. Scalability
    • Design as stackable module; additional sensor “shields” on same I²C bus.
    • Upgrade to ESP32-C3 (RISC-V, BLE5 LE) for lower power and Matter/Thread compatibility.
7. Conclusion
The current schematic provides a solid foundation for an IoT-connected environmental exposure meter with solar charging and dual-sensor support. Key strengths are the use of a proven ESP32 module and MPPT charger. Addressing power-path efficiency, decoupling, and DRC issues will greatly improve reliability. With iterative hardware tweaks and richer firmware, the design can scale into a versatile platform for portable air-quality and UV monitoring in consumer, educational, or occupational-safety settings.
Optimize power design
Improve decoupling strategy
Address RF interference
Reassess sensor interface
345 days
Sign up to send
SL1
UART0_RX
U1
Manufacturer Part Number
AP2112K-3.3TRG1
SW2
ESP32_EN
UART0_TX
UART0_RX
+3.3V
BOOST_EN
+3.3V
ESP32_EN
ESP32_RX2
RTS
ESP32_EN
UART0_TX
IO0
ESP32/I2C_SCL
+3.3V
ESP32/I2C_SDA
SW1
ESP32_TX2
VBAT
+3.3V
DTR
ESP32/I2C_SCL
+3.3V
+3.3V
DTR
ESP32/I2C_SDA
BOOST_EN
VBOOST
ESP32_RX2
+3.3V
IO0
VBAT
ESP32_TX2
ESP32/I2C_SCL
IO0
RTS
ESP32/I2C_SDA
VBOOST
Note 1
Line 1
Sensor MH-19
Line 2
Intelligent Infrared CO2 Module
Line 3
------------------------------------------------------------
Line 4
https://www.winsen-sensor.com/d/files/PDF/Infrared%20Gas%20Sensor/NDIR%20CO2%20SENSOR/MH-Z19%20CO2%20Ver1.0.pdf
J1
Note 2
Line 2
Sensor VEML6075
Line 3
UV Light Sensor
Line 4
-----------------------------------------------------------
Line 5
https://www.sparkfun.com/products/15089
LED1
U2
J3
J2
C1
Capacitance
1uF
R4
Resistance
10KΩ
J5
R1
Resistance
1KΩ
Q3
Manufacturer Part Number
BSS138
R3
Resistance
10KΩ
Q2
Manufacturer Part Number
BSS138
C2
Capacitance
1uF
J6
  • Ground
    Ground
    A common return path for electric current. Commonly known as ground.
    jharwinbarrozo
    20.5M
  • Net Portal
    Net Portal
    Wirelessly connects nets on schematic. Used to organize schematics and separate functional blocks. To wirelessly connect net portals, give them same designator. #portal
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    43.0M
  • Power Net Portal
    Power Net Portal
    Wirelessly connects power nets on schematic. Identical to the net portal, but with a power symbol. Used to organize schematics and separate functional blocks. To wirelessly connect power net portals, give them the same designator. #portal #power
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  • Generic Resistor
    Generic Resistor
    A generic fixed resistor ideal for rapid circuit topology development. Its footprint automatically adapts based on the selected package case code—supporting 0402, 0603, 0805, 1203, and many other standard SMD packages, as well as axial horizontal and vertical configurations. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard resistor values: 1.0 ohm, 10 ohm, 100 ohm, 1.0k ohm, 10k ohm, 100k ohm, 1.0M ohm 1.1 ohm, 11 ohm, 110 ohm, 1.1k ohm, 11k ohm, 110k ohm, 1.1M ohm 1.2 ohm, 12 ohm, 120 ohm, 1.2k ohm, 12k ohm, 120k ohm, 1.2M ohm 1.3 ohm, 13 ohm, 130 ohm, 1.3k ohm, 13k ohm, 130k ohm, 1.3M ohm 1.5 ohm, 15 ohm, 150 ohm, 1.5k ohm, 15k ohm, 150k ohm, 1.5M ohm 1.6 ohm, 16 ohm, 160 ohm, 1.6k ohm, 16k ohm, 160k ohm, 1.6M ohm 1.8 ohm, 18 ohm, 180 ohm, 1.8K ohm, 18k ohm, 180k ohm, 1.8M ohm 2.0 ohm, 20 ohm, 200 ohm, 2.0k ohm, 20k ohm, 200k ohm, 2.0M ohm 2.2 ohm, 22 ohm, 220 ohm, 2.2k ohm, 22k ohm, 220k ohm, 2.2M ohm 2.4 ohm, 24 ohm, 240 ohm, 2.4k ohm, 24k ohm, 240k ohm, 2.4M ohm 2.7 ohm, 27 ohm, 270 ohm, 2.7k ohm, 27k ohm, 270k ohm, 2.7M ohm 3.0 ohm, 30 ohm, 300 ohm, 3.0K ohm, 30K ohm, 300K ohm, 3.0M ohm 3.3 ohm, 33 ohm, 330 ohm, 3.3k ohm, 33k ohm, 330k ohm, 3.3M ohm 3.6 ohm, 36 ohm, 360 ohm, 3.6k ohm, 36k ohm, 360k ohm, 3.6M ohm 3.9 ohm, 39 ohm, 390 ohm, 3.9k ohm, 39k ohm, 390k ohm, 3.9M ohm 4.3 ohm, 43 ohm, 430 ohm, 4.3k ohm, 43K ohm, 430K ohm, 4.3M ohm 4.7 ohm, 47 ohm, 470 ohm, 4.7k ohm, 47k ohm, 470k ohm, 4.7M ohm 5.1 ohm, 51 ohm, 510 ohm, 5.1k ohm, 51k ohm, 510k ohm, 5.1M ohm 5.6 ohm, 56 ohm, 560 ohm, 5.6k ohm, 56k ohm, 560k ohm, 5.6M ohm 6.2 ohm, 62 ohm, 620 ohm, 6.2k ohm, 62K ohm, 620K ohm, 6.2M ohm 6.8 ohm, 68 ohm, 680 ohm, 6.8k ohm, 68k ohm, 680k ohm, 6.8M ohm 7.5 ohm, 75 ohm, 750 ohm, 7.5k ohm, 75k ohm, 750k ohm, 7.5M ohm 8.2 ohm, 82 ohm, 820 ohm, 8.2k ohm, 82k ohm, 820k ohm, 8.2M ohm 9.1 ohm, 91 ohm, 910 ohm, 9.1k ohm, 91k ohm, 910k ohm, 9.1M ohm #generics #CommonPartsLibrary
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  • Generic Capacitor
    Generic Capacitor
    A generic fixed capacitor ideal for rapid circuit topology development. You can choose between polarized and non-polarized types, its symbol and the footprint will automatically adapt based on your selection. Supported options include standard SMD sizes for ceramic capacitors (e.g., 0402, 0603, 0805), SMD sizes for aluminum electrolytic capacitors, and through-hole footprints for polarized capacitors. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard capacitor values: 1.0pF, 10pF, 100pF, 1000pF, 0.01uF, 0.1uF, 1.0uF, 10uF, 100uF, 1000uF, 10000uF 1.1pF, 11pF, 110pF, 1100pF 1.2pF, 12pF, 120pF, 1200pF 1.3pF, 13pF, 130pF, 1300pF 1.5pF, 15pF, 150pF, 1500pF, 0.015uF, 0.15uF, 1.5uF, 15uF, 150uF, 1500uF 1.6pF, 16pF, 160pF, 1600pF 1.8pF, 18pF, 180pF, 1800pF 2.0pF, 20pF, 200pF, 2000pF 2.2pF, 22pF, 220pF, 2200pF, 0.022uF, 0.22uF, 2.2uF, 22uF, 220uF, 2200uF 2.4pF, 24pF, 240pF, 2400pF 2.7pF, 27pF, 270pF, 2700pF 3.0pF, 30pF, 300pF, 3000pF 3.3pF, 33pF, 330pF, 3300pF, 0.033uF, 0.33uF, 3.3uF, 33uF, 330uF, 3300uF 3.6pF, 36pF, 360pF, 3600pF 3.9pF, 39pF, 390pF, 3900pF 4.3pF, 43pF, 430pF, 4300pF 4.7pF, 47pF, 470pF, 4700pF, 0.047uF, 0.47uF, 4.7uF, 47uF, 470uF, 4700uF 5.1pF, 51pF, 510pF, 5100pF 5.6pF, 56pF, 560pF, 5600pF 6.2pF, 62pF, 620pF, 6200pF 6.8pF, 68pF, 680pF, 6800pF, 0.068uF, 0.68uF, 6.8uF, 68uF, 680uF, 6800uF 7.5pF, 75pF, 750pF, 7500pF 8.2pF, 82pF, 820pF, 8200pF 9.1pF, 91pF, 910pF, 9100pF #generics #CommonPartsLibrary
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  • Generic Inductor
    Generic Inductor
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  • Terminal
    Terminal
    An electrical connector acting as reusable interface to a conductor and creating a point where external circuits can be connected.
    natarius
  • RMCF0805JT47K0
    RMCF0805JT47K0
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  • 875105359001
    875105359001
    10uF Capacitor Aluminum Polymer 20% 16V SMD 5x5.3mm #forLedBlink #commonpartslibrary #capacitor #aluminumpolymer #radialcan
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  • CTL1206FYW1T
    CTL1206FYW1T
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ENVIRONMENTAL EXPOSURE RISK METER

ENVIRONMENTAL EXPOSURE RISK METER thumbnail
Environmental exposure risk measuring device based on ESP32, ultraviolet light (UV) and CO2 gas sensor modules. It has a voltage booster based on MT3608 chip and a solar panel lithium battery charger with MPPT based on CN3791 chip.

Properties

Properties describe core aspects of the project.

Pricing & Availability

Distributor

Qty 1

Arrow

$0.46–$0.79

Digi-Key

$1.53–$9.74

LCSC

$6.21–$6.31

Mouser

$0.60

Verical

$0.35–$0.65

Controls