Simulink & Arduino losing precision with multiple digital input blocks

Hi everyone, I have an issue with losing precision using a TTL pulse for synchronization using Simulink & Arduino.

For context: I want to synchronize a recording of brain activity to other measurements I am performing. For this, I am sending a semi-random pulse using Arduino_01 to the hardware recording brain activity (IMEC-PXIe Acquisition module), while also sending it to Arduino_02 that I’m using as DAQ, recording timestamps for pulses, speed on a wheel, and other measurements. (See Figure 01 for recording hardware diagram)

This works fine when Arduino_02 only records the TTL pulse, i.e., using a single Digital Input Arduino block. (Figure 02).

However, when I include other digital input blocks (to record other signals), it seems as if the sampling of the TTL pulse is reduced, leading to a different number of pulses between the IMEC module and the data recorded on MATLAB . (See Figure 03 to illustrate the effects of the problem).

I explored other alternatives, such as using an NI-USB-6001 to do the same, but I ran into the exact same situation: When using more than one digital input, it’s as if there is a loss in the sampling at which the TTL is being record. Any help would be greatly appreciated since I really don’t have an idea of how to solve this issue.

[Arun Kumar]

Hi Lucis,

Please consider using External Interrupt block available in the Simulink support packge for Arduino hardware and see if you face the same issue.

https://www.mathworks.com/help/supportpkg/arduino/ref/externalinterrupt.html