Data Acquisition System With Controller Area Network and SD Card

ajay_bhargav
Sun Nov 08 2009, 02:09 am

This project implements a high speed data acquisition system using Mega32 microcontrollers and a Controller Area Network (CAN).

Recording data is essential to testing and developing a racecar. Recording what each sensor is doing can tell an engineering how the car is performing, and most importantly, how to make it faster. A well outfitted car can have many sensors, with Formula One cars having well over 100 sensors. Cornellâ€™s FSAE car has over 50 sensors on it, many of which require high sampling rates to be useful. Commercial data acquisition systems are either expensive, slow, or have few inputs. A solution to this problem had been attempted by previous 476 students (Karl Antle and Ryan Mcdaniel) using a PIC18F2585, but it was only able to log reliably at 150 Hz. Many sensors on the car require much higher sampling rates, as the sensors are recording events occurring in a very short period of time. For example, when looking at a sharp bump using rocker position the event may only last .05 seconds when driving quickly. If taking the derivative of the data a very high sampling rate is required to give useful data, at least 500 Hz. It was this need for high speed data acquisition that motivated us to create a high speed data acquisition system to replace the current one.

Our system uses multiple transmitter nodes to acquire data from sensors and transmit the data in packets over a CAN bus. Each transmitter consists of a Mega32 microcontroller, an external Analog-to-Digital converter, a CAN controller and a CAN transceiver. The CAN packets are received by a single receiver node and stored to a Secure Digital (SD) card. The receiver node consists of a 2 Mega32s, a CAN controller, a CAN transceiver, and a SD card. The goal of the project was to create a system which can record 32 10 bit ADC channels recorded by 4 Mega32s and transmitted over the CAN bus. In addition, the system should be expandable to accept CAN packets sent from other modules, such as an ECM or a standalone O2 unit. 500 Hz on the 32 AD channels was set as a goal for sampling frequency.