General log¶
Week 1 : Preliminary concept sketch¶
Problem :
Mobile street vending is widespread globally, yet many lack reliable (and safe) access to affordable electricity especially during evening and night-time trading hours
Target user characteristics :
- Trade mostly in the evening
- Daily-based income
- Limited technical knowledge
Solution :
Plug and play, pay-as-you-go (pay amount based on usage or time for example daily, weekly or monthly) solar PV system for essential lighting and load appliances of the street, inspired by implementation in Africa.
Main features :
- Solar panel with built-in axis tracker for optimal energy capture in the morning before use during night-time trading hours.
- Smart controller that enables flexible installment payments (pay-as-you-go) without upfront cost and embedded security features.
Week 2 : Consultation at SEEED studio¶
First consultation on the final project with Matthew, the Fab Academy 2026 instructor for ChaiHuo makerspace, was done at the SEEED studio (check out @timmili_makers week 2 to get a peek)!
The following topics were discussed :
- Work breakdown ; the following upcoming sections will be organized around these four main building blocks: SBC, MCU, power supply, and payment system (see respective logs for detailed research)
- Focus will be on building a small, simple prototype first, with further expansion planned after gaining insights from the initial
- Materials required for the first prototype
Updates :
- MCU + peripherals: -
- SBC : -
- Power supply : -
- Payment system : -
Week 3 : Components acquired, initiate prototype testing¶
The following components were sourced from Taobao. Specifications on it could be seen below :
| Component | Specifications / Notes | Quantity | Additional Details |
|---|---|---|---|
| Photoresistor | Light-dependent resistor, Vin : 3.3~5.5 V | 1 | Detects light intensity |
| Servo motor | Vin : 4.8–6 V | 1 | Used to adjust solar panel orientation |
| Solar Panel | Voc : 9 V, Isc : 1.23 A, 220 x 340 x 3 mm | 1 | Converts sunlight to electrical energy to charge battery |
| Solar voltage Regulator | Vin : 9-30 V, Output (V A): 5 V 3 A, 9 V 2 A, 12 V 1.5 V | 1 | Stabilizes voltage for MCU and sensors |
| Battery | Vout: 5V, Iout : 2.5~3A, Li-ion, 6800 mAh | 1 | Powers the system despite when sunlight is low |
Regarding Voc and Isc
-
VOC (Open-Circuit Voltage):
This is the maximum voltage the solar panel can produce when no current is drawn (open circuit). It represents the upper voltage limit of the panel. -
ISC (Short-Circuit Current):
This is the maximum current the solar panel can produce when the terminals are shorted together (voltage = 0). It represents the highest current the panel can deliver under full sunlight. It is used to size fuses, wires, and regulators safely.
Source: ChatGPT by OpenAI, February 2026
Updates :
- MCU + peripherals : -
- SBC : -
- Power supply : -
- Payment system : -
- It was decided that the preliminary prototype should prioritize offline device activation, with the concept centered on token generation and matching to unlock the device. Further details can be found under the Details: Payment system tab.
Week 4 : MCU, servo motor, and light direction testing¶
The components purchased during Week 3 were used as the basis for the initial benchmarking experiments. This week focuses on comparing different motor types and light-sensitive sensors in order to better evaluate the suitability of the selected components for the intended final project application. In addition, the interface of these components with the MCU is also tested to verify integration and communication.
Lessons learned : All components and the microcontroller must share the same reference point (common ground)
Updates :
- MCU + peripherals :
- Comparison of motors and light-sensitive sensors
- The connection and communication between the XIAO ESP32C3 MCU, servo motor and two light direction systems were tested. Test results could be seen at the Week 4 : Embedded programming documentation.
- SBC : -
- Power supply : -
- Payment system : -
Week 5 : Solar charging path revision¶
Compact size and low weight are prioritised over the solar panel's ability to fully charge the battery within a single day. The focus this week is therefore to validate the chain from the solar panel to the battery charging system to ensure that it operates correctly and behaves reliably under real-world conditions. During outdoor testing, some technical issues were identified specifically on the compatibility between the solar regulator and solar panel, as well as the battery management system (BMS) of the purchased battery pack.
| Component | Specifications / Notes | Quantity | Additional Details |
|---|---|---|---|
| Photoresistor | LLight-dependent resistor, Vin : 3.3~5.5 V | 1 | Detects light intensity |
| Servo motor | Vin : 4.8–6 V | 2 | Used to adjust solar panel orientation |
| Solar Panel | Voc : 9 V, Isc : 1.23 A, 220 x 340 x 3 mm | 1 | Converts sunlight to electrical energy to charge battery |
| Solar Regulator (Replaced) | Vin : DC 5–36 V, Vout : 5 V, Iout : 2-3 A | 1 | Stabilizes voltage for MCU and sensors |
| Battery Pack (Replaced) | Vin, Iin : 5 V, 2 A, Vout, I out : 5V 5A, pass through/UPS | 1 | Powers the system despite when sunlight is low |
Updates :
- MCU + peripherals :
- SBC : -
- Power supply : Revision on solar regulator and battery pack
- Payment system : -
Week 6 : First PCB design¶
A first revision was designed that integrates four phototransistor channels and two SG5010 servo outputs - result could be seen at Week 6 : Electronics Design. It is worth to note that the power for the system comes from a bench DC supply and 5 V for the servos is taken from the XIAO RP2040's 5 V pin.
Improvements to be made :
- Replacing the bench supply with a battery-based power path so that it matches expected deployment scenario
- Route servo motor current on a dedicated 5 V rail as the RP2040 potentially could not provide sufficient amps
At this stage, the design does not yet incorporate additional resistor networks. Therefore, a more in-depth investigation was conducted to better understand how they could be integrated into future revisions of the system.
Updates :
- MCU + peripherals : Deep dive on resistors
- SBC : -
- Power supply : -
- Payment system : -
Week 7 :¶
The next focus is to better understand MOSFET-based switching circuits to enable remote control on power management of the solar pv system.
Updates :
- MCU + peripherals : -
- SBC : -
- Power supply : Deep dive on MOSFETS
- Payment system : -
Week 8 :¶
The next focus is to better understand capacitor behavior to stabilise the power management of the solar PV system.
Updates :
- MCU + peripherals : -
- SBC : -
- Power supply : Deep dive on capacitors
- Payment system : -