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Questions about the sessantaquattro AUX channel

I have bought a sessantaquattro+ recently for torque experiment. There is a problem when i try to synchronize the torque signals and the hd-emg signals. I learned that there are two AUX A/D channels on the adapter. I want to send a trigger signal to one of the AUX channels when the torque is sampled through stm32 (the hd-emg sampling starts earlier, thus the emg signal before the trigger is needless). But the OT Biolab+ shows that the AUX channels have a voltage of 3.26V even there is no signal. And when i choose ISO-AUX in the configuration page in the OT Biolab+, the voltage changes to 5V roughly. I wonder if there are some setup steps i missed when using the AUX or the AUX channel can only be used with auxiliary equipment.

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The sessantaquattro AUX-IN input range is +/-3.3V. When no signal is provided (the input is left floating) the input can drift up to one rail, in your case the positive rail, and you read a saturated signal close to 3.3V.

When you set in the OT BioLab+ setup the ISO-AUX, the software use a conversion factor of 1.5 (the ISO aux accept inputs from -5V to +5V and "remap" the voltage to the +/-3.3V). So is the same as before, but with a larger input range.

From the picture, it seems you are providing only GND to the AUX-IN. You need to add a second wire with the signal to one of the two jack rings. On the user manual see page 21 on the rigth with details and pin-out.

Lastly, consider that the sessantaquattro must remain floating. You cannot connect to the AUX something if it is not battery powered or electrically insulated from any other power source. See again the user manual on page 9.

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