SparkFun Forums

[John Polk]

I'm using multiple (6) independent OLA with built in IMUs to capture motion across body sites. Is there a way to deliver a synchronized signal (depolarization) or effectively 'push' the reset buttons simultaneously? Devices are not currently wired together. I saw a query on this in a forum post from 2020 but no published result. Grateful for advice.

[YellowDog]

I suspect it's not in the firmware but if you can set the clock via a ttl serial gps, you could use that to synchronize all the ola boards connected to a single gps receiver.

[PaulZC]

Hi @ John Polk,

How close do you need the synchronisation to be? Is to-the-nearest-second close enough? Or do you need more like millisecond synchronisation?

The OLA does have a trigger-on-pulse feature that might do what you need. But you would need to interconnect all six OLAs to a simple pulse generator for this to work.

Best wishes,
Paul

[John Polk]

Thank you Paul and Yellowdog!

[PaulZC]

Hi @ John Polk,

Thanks for your private message. Let's continue the discussion here, then everyone gets to benefit from it.

Please tell us more about your application. Specifically:
How fast do you need to sample the IMUs? Is 1Hz OK, or are you aiming for more like 100Hz?
Do you need each and every sample to be synchronised and time-stamped, so you can align the data in post processing?

The trigger-reading-on-pin feature may work for you. If you select that mode on all the OLAs and then link them all to a simple square wave signal, they will all take their samples at the same point in time. But the clock time would need to be accurately set on all six too. That's tricky to do at the 1/100th of a second level.

Instead it might be better to:
Synchronise the clocks manually as best you can. Hopefully you can get them aligned to the nearest second.
Set the logging interval at whatever rate you need. Set it the same on all six. Log the IMU values, RTC time and microseconds. Also log one of the analog inputs.
Assemble a simple 3.3V square wave generator. Set it to 1Hz. Any microcontroller board can do this. The Pulse Per Second from a cheap GNSS chip would also work. Connect the square wave to the analog inputs on all six OLAs. Connect GND too - two thin wires to each OLA.
In your post-processing, the clocks will be aligned to the nearest second (approx.). Look for the rising / falling edges of the analog input in the data from each, and use that to accurately synchronise the data from all six. 'Nudge' the data samples in time until the rising edges align in the data.

I hope this helps,
Paul