MCUs in E-Bikes: driving lights, LED/LCD display and measurements

June 20, 2013 //By Ronak Desai, Cypress Semiconductors
MCUs in E-Bikes: driving lights, LED/LCD display and measurements
This article explores design techniques and challenges for implementing an electronic bike (E-Bike) built using a microcontroller or Programmable System on Chip (PSoC). Current E-Bike systems use a microcontroller with external signal conditioning and comparator circuitry to drive the three-phase motor; external ADC and external amplifiers for different sensor inputs; relay driver circuitry for brake light, headlight, and directional lights; LED/ LCD displays; and temperature measurement.

Programmable SOC devices can be used in E-Bike applications as a single-board system for motor control, analog measurement, and direct drive LCD display. Programmable SOCs can also support capacitive sensing technology to replace mechanical buttons on the keypad. In addition, SOC devices use internal PWM, MUX, and comparators for driving and controlling the three-phase motor, internal ADC and PGA for sensor inputs battery monitoring, and temperature sensing using a temperature sensing device like a thermistor or RTD. The device can also directly drive the relays for the brake light, headlight, and directional lights, as well as direct drives the LCD display of temperature, battery status, speed, distance travelled, and any error/warning messages.

Using IDE-based tools, all interface and logic can be designed for the SoC. These tools also have readily available component blocks for designing more complex logic such as monitoring a capacitive sensor for the interface, an ADC for analog sensors and other inputs, driving the PWM for a buzzer, DAC, and a segment, character, or graphical LCD display. Thus, with a programmable SOC, the development and product cost of an E-Bike system can be substantially reduced.

Figure 1 shows the block diagram of a basic E-Bike system

Microcontroller: The microcontroller is typically used for different sensor input detection (i.e., throttle inputs, temperature sensor, battery input, fuel sensor, obstacle sensors), A/D conversion, output comparison components, and driving and controlling the three-phase brushless automotive motor. An ultra-low power microcontroller is required as an E-Bike is a battery-operated system. The microcontroller is also part of the central locking system, and can be used to communicate with different external devices used in the vehicle. Using a microcontroller whenever a brake is pulled automatically stops the motor spinning and prevents the motor from wearing down the brake pads faster than a standard human-powered bike.

Hub motor/Wheel motor: Typically, a brushless motor is used, either sensored (Hall Effect) or sensorless, for reliable and efficient

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