Synchronizing NI CompactDAQ and CAN Measurements for In-Vehicle Data Logging

NI CompactDAQ is an ideal platform for in-vehicle data acquisition and logging. Often times, it is desirable to synchronize analog and digital measurements with CAN. This document discusses how NI CompactDAQ measurements can be synchronized with CAN I/O using NI PCMCIA-CAN interfaces.

Required Hardware

In addition to an NI CompactDAQ chassis and the I/O modules of your preference, the following equipment is required for CAN and NI CompactDAQ synchronization:

• NI 9401 – 8-Channel, 5 V/TTL High-Speed Bidirectional Digital I/O Module
• Any NI PCMCIA-CAN Series 2 Interface
• NI PCMCIA-CAN Synchronization Cable

2-port, NI PCMCIA-CAN card with synchronization cable	NI 9401 – 8-channel digital I/O

Additional Resources:
NI 9401 Model Page
NI PCMCIA-CAN Interfaces (syncronization cable is an accessory)

Hardware Setup

To achieve true hardware synchronization between NI CompactDAQ measurements and CAN data, the NI PCMCIA-CAN card uses the onboard NI CompactDAQ clock. To export this clock from NI CompactDAQ, an NI 9401 digital I/O module needs to be placed in either slot five or six of the NI CompactDAQ chassis. These two slots allow the onboard clock to be routed to a RTSI line, which in turn, allows the clock to be exported on a digital line. All other I/O modules can be placed in any of the remaining seven slots.

To connect the PCMCIA-CAN card to the NI CompactDAQ chassis, follow the directions below:

1. Connect the Trig7_CLK wire to Pin 17 of the NI 9401 digital I/O module.
2. Connect the Trig 0 wire to Pin 14 of the NI 9401 digital I/O module.
3. Connect one of the GND wires to Pin 13 of the NI 9401 digital I/O module.

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Figure 1. Wiring Diagram for NI CompactDAQ and a PCMCIA-CAN Card

Programming

The NI-CAN driver installs numerous example programs for creating applications with CAN and data acquisition (DAQ) hardware synchronization. These example programs are located in the example finder under the following section and include:

Hardware Input and Output >> CAN >> Channel API >> Synchronizing with DAQ >> DAQmx

To create an application with synchronized NI CompactDAQ and CAN measurements, the vast majority of the program remains the same as the examples listed above. The only difference is that NI CompactDAQ does not natively export a clock, such as with RTSI on PCI and with the timing and synchronization buses for PXI. To expose the NI CompactDAQ onboard clock and route it to a digital output line, simply replace the “CAN Sync with DAQmx.vi” with the “CAN Sync with CompactDAQ.vi” from the linked example program below.

The “CAN Sync with CompactDAQ.vi” has an additional input for clock frequency. When replacing the “CAN Sync with DAQmx.vi” with “CAN Sync with CompactDAQ.vi,” make sure to add a control for the “Freqout Input” parameter. With this control, you can specify what digital line the clock will be exported on.

Additional Resources:
NI CAN Software and Hardware Products
NI CompactDAQ Homepage
Synchronizing CAN and Analog Signals for Device Validation

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