Parkside Multi Charger: Controller Architecture for the Basic and Pro Versions

Development of the Parkside Multi Charger has entered a new stage. During the latest planning phase, several controller and power-switching architectures were compared to find a solution that keeps the Basic version easy to build while leaving enough room for the more advanced Pro model.

The goal of the project is to create an eight-slot charging station that uses an original Parkside charger and automatically switches it between the installed battery packs. The actual charging process and the related safety functions remain under the control of the original charger electronics.

How the Basic Version Works

The factory charger has two status LEDs. The controller determines the condition of the currently selected battery by monitoring these LEDs.

Factory charger LED	Meaning	Controller response
Solid green	The battery is charged, or the slot is empty	Move to the next battery slot
Solid red	Charging is in progress	Remain on the current battery and wait for green
Flashing red	Overheated or faulty battery	Move on after ten flashes and increase the error counter

The charger LEDs are monitored by two GL5516 light-dependent resistors. Each sensor is installed in a light-blocking enclosure directly above the factory red or green LED.

Battery Slot Status Indication

Each of the eight battery slots receives its own addressable RGB status LED.

Colour	Status
Blue	Charging in progress
Green	Charging completed successfully
Flashing red	Temporary error or overheated battery
Solid red	Permanent battery error after five failed attempts
Off	Empty or not yet identified slot

An empty slot and an already charged battery may both produce the same green indication on the factory charger. The controller therefore marks a slot as charged only when a solid red charging state was detected during the previous two hours and was later followed by a green state.

Rethinking the Power Switching System

The original concept used separate mechanical relays to switch every conductor of every battery. With four switched wires per battery, this would require 32 separate relays.

8 battery slots x 4 switched wires = 32 separate switching elements

Further analysis showed that three conductors are the most important from a switching perspective:

• 20 V positive power line
• 20 V negative power line
• ID or communication line

The current hybrid concept uses MOSFET switching for the two high-current power lines and a mechanical relay for the ID line.

Factory charger 20 V+ -> MOSFET switch -> selected battery 20 V+ Factory charger 20 V- -> MOSFET switch -> selected battery 20 V- Factory charger ID -> mechanical relay -> selected battery ID

A mechanical relay is preferred for the ID line because it provides a true open circuit when disabled and does not distort the communication waveform between the charger and the battery.

MOSFET or Mechanical Relay?

Property	MOSFET	Mechanical relay
Switching noise	Silent	Audible click
Service life	No mechanical wear	Limited mechanical switching life
Switching speed	Very fast	Slower
Galvanic isolation	Not automatically provided	True open contact
Body diode	Must be considered	Not present
ID or communication line	Only with a suitable topology	Well suited

Back-to-back MOSFET switching will probably be required on the power lines to provide true bidirectional isolation. A single MOSFET contains a body diode that may continue to provide a current path in one direction even when the transistor is switched off.

Basic Version: ESP32 and Arduino Nano

For the first Basic prototype, the combination of an ESP32 and an Arduino Nano currently appears to offer the best compromise.

ESP32 | +-- Wi-Fi +-- bilingual web interface +-- factory charger LED monitoring +-- charging state machine +-- error-cycle management | +-- UART connection | +-- Arduino Nano | +-- 8 positive power switches +-- 8 negative power switches +-- 8 addressable RGB LEDs +-- battery-slot temperature monitoring +-- system cooling control +-- watchdog and emergency shutdown

ESP32 Responsibilities

• Managing the Wi-Fi connection
• Providing the Hungarian and English web interface
• Monitoring the red and green LEDs of the factory charger
• Selecting the active battery slot
• Running the charging and fault-management state machine
• Supervising the Nano and displaying system information

Arduino Nano Responsibilities

• Controlling the positive and negative power switches
• Executing the safe switching sequence
• Driving the eight battery-slot RGB LEDs
• Optional battery-slot temperature monitoring
• Controlling the system cooling fan
• Disconnecting the power paths if communication is lost
• Local watchdog and overtemperature protection

Advantages

• Networking and low-level hardware control are clearly separated
• The Nano can safely disconnect the power paths if the ESP32 restarts or freezes
• Temperature sensors and cooling control can be added easily
• The prototype can be built from inexpensive and widely available development boards
• The firmware is divided into two clearly defined parts

Disadvantages

• Two separate firmware projects must be maintained
• A communication protocol is required between the ESP32 and the Nano
• The 3.3 V and 5 V logic levels must be matched safely
• The additional controller introduces more components and possible failure points

Alternative: A Single ESP32

A single ESP32 could also control the complete system with the help of output expanders such as the 74HC595 or MCP23017.

Advantages

• Only one firmware project
• Fewer microcontrollers
• No inter-controller communication protocol
• Lower component cost

Disadvantages

• Wi-Fi, web serving and power control run on the same MCU
• There is no separate safety controller if the ESP32 fails
• Output expanders quickly become necessary as the number of peripherals increases
• Networking tasks and hardware timing may affect each other

Alternative: STM32F4xx

We also investigated whether an STM32F4xx microcontroller could replace the ESP32 and Arduino Nano combination.

A larger STM32F4 device, such as the STM32F407VET6 or STM32F407VGT6, provides enough GPIOs, timers, ADC channels and communication interfaces to control the entire hardware platform from a single processor.

Advantages

• Large GPIO capacity
• Powerful Cortex-M4 processor
• Excellent real-time control
• Advanced timers, ADCs, DMA and watchdog peripherals
• The complete hardware can be managed by one state machine
• Well suited for a professional custom PCB

Disadvantages

• STM32F4 devices do not include integrated Wi-Fi
• An external ESP8266, ESP32 or other network module is required
• Web-server development is considerably more complex
• Development and debugging will take longer
• Prototype construction is less immediate than with the Arduino ecosystem

Controller Architecture Comparison

Property	Single ESP32	ESP32 + Nano	STM32F4xx
Integrated Wi-Fi	Yes	Yes, through the ESP32	No
Number of MCUs	1	2	1, plus a network module
GPIO capacity	Limited	Sufficient when divided	High
Development speed	Fast	Fast	Slower
Safety separation	Limited	Good	Handled within one MCU
Firmware complexity	Medium	Two separate firmware projects	Higher
Prototype suitability	Good	Very good	Moderate
Custom production PCB	Good	Good	Very good

The Pro Version

The Parkside Multi Charger Pro will not simply be an expanded Basic model. It will be a more advanced charging and battery-management platform.

The current Pro concept uses an ESP32 and an Arduino Mega 2560.

ESP32 | +-- Wi-Fi +-- Bluetooth +-- web interface +-- MQTT and Home Assistant +-- central display +-- data logging | +-- UART connection | +-- Arduino Mega 2560 | +-- two simultaneous charging channels +-- voltage and current measurement +-- RFID readers +-- temperature sensors +-- DC-DC module control +-- cooling fans +-- hardware safety system

Why Use a Mega in the Pro Version?

• Large number of digital and analogue inputs
• Multiple hardware UART interfaces
• Simple integration of many peripherals
• Well suited for RFID, measurement and cooling tasks
• Fast prototype development

Current Decision

Development of the first Basic prototype will continue with the following architecture:

• ESP32: Wi-Fi, web interface, charger LED monitoring and high-level charging logic
• Arduino Nano: power switches, RGB LEDs, temperature monitoring, cooling and safety functions
• MOSFET switches: 20 V positive and negative power paths
• Mechanical relays: isolation of the ID communication lines

The STM32F4xx option has not been rejected. It may become a serious alternative for a later custom-PCB version, especially if the complete low-level hardware control is moved to a more professional microcontroller platform.

Next Development Steps

• Develop the communication protocol between the ESP32 and the Nano
• Test bidirectional isolation of the MOSFET switches
• Test switching behaviour of the ID line
• Measure the temperature of the power switches under load
• Size and test the system cooling
• Assemble the first two-channel test bench
• Design the final eight-channel prototype

The project remains under active development. The hardware architecture may still change based on measurement results and practical testing.