Synchronizing 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 CompactDAQ measurements can be synchronized with CAN I/O using NI PCMCIA-CAN interfaces.

Required Hardware

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

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

See Also:
NI 9401 Model Page
NI PCMCIA-CAN Interfaces (Syncronization cable is an accessory)

Hardware Setup

To achieve true hardware synchronization between CompactDAQ measurements and CAN data, the NI PCMCIA-CAN card will utilize the onboard CompactDAQ clock. To export this clock from CompactDAQ, an NI 9401 digital I/O module needs to be placed in either slot 5 or 6 of the CompactDAQ chassis. These 2 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 7 slots.

To connect the PCMCIA-CAN card to the 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.

The NI-CAN driver installs numerous example programs for creating applications with CAN and 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 CompactDAQ and CAN measurements, the vast majority of the program will remain the same as the examples listed above. The only difference, however, is that 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 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. This control will allow you to specify what digital line the clock will be exported on.

Related Links:
NI CAN Software and Hardware Products
NI CompactDAQ Homepage
Synchronizing CAN and Analog Signals for Device Validation

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