Analog signal offset at -5V and saturation in Open Ephys

[Esteban Merino]

Hi everyone,

I have a question regarding my setup. I am currently sending the analog signal from a treadmill through a coaxial connector to the I/O board, and from there into Open Ephys.

I’m able to visualize the signal in the LFP viewer without issues. However, the direction signal (ADC2) appears highly saturated, and I cannot properly see the scale for that channel. Additionally, the mean of the signal is negative.

Although not shown here, the speed signal (on ADC1) shows a similar issue: it is centered around -5 V and increases from there, but always returns back to -5 V baseline.

I have also plotted the raw signals, and indeed all values sit at around -5 V when the treadmill is not moving.

Has anyone experienced something similar or knows what might be causing this offset/saturation issue?

Thanks in advance!

[Josh Siegle]

Hi Esteban,

Do the recorded signals have the same issue? Or do you think this is a display issue?

And have you tried acquiring the two signals with an oscilloscope to see how they differ from what appears in the LFP Viewer? It would be helpful to know what the expected output is.

Best,

Josh

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[Esteban Merino]

Hi Josh,

There are no issues when I record the raw data; the signals look fine and I don’t observe any problems in that regard. The signal has the expected shape from the running wheel: a rising or falling (more or less continuous) pulse when measuring speed, and a square pulse when the movement is forward or backward.

Additionally, what I observe on the oscilloscope is consistent with what I see in Open Ephys—the signal shape is the same in both cases. I also measured the voltage reaching the connectors during the speed and distance measurements, and it is in the expected range of approximately 0 to 3 mV.

For this reason, I think the issue is related to Open Ephys (or how the signal is being visualized/acquired). Specifically, the signal is not centered around 0 when recorded in Open Ephys. This causes the direction pulses to shift to very high values when the treadmill is moving, while in the absence of movement the signal sits around -5.

I have tried applying a filter beforehand, and in that case the signal does get centered around 0, but the pulse shape becomes significantly distorted as a result.

Thanks for you response!

El jueves, 26 de marzo de 2026 a las 9:13:12 UTC-7, Josh Siegle escribió:

Hi Esteban,

Do the recorded signals have the same issue? Or do you think this is a display issue?

And have you tried acquiring the two signals with an oscilloscope to see how they differ from what appears in the LFP Viewer? It would be helpful to know what the expected output is.

Best,

Josh

On Wed, Mar 25, 2026 at 5:14 PM, Esteban Merino <emerin...@gmail.com> wrote:

Hi everyone,

I have a question regarding my setup. I am currently sending the analog signal from a treadmill through a coaxial connector to the I/O board, and from there into Open Ephys.

I’m able to visualize the signal in the LFP viewer without issues. However, the direction signal (ADC2) appears highly saturated, and I cannot properly see the scale for that channel. Additionally, the mean of the signal is negative.

Although not shown here, the speed signal (on ADC1) shows a similar issue: it is centered around -5 V and increases from there, but always returns back to -5 V baseline.

I have also plotted the raw signals, and indeed all values sit at around -5 V when the treadmill is not moving.

Has anyone experienced something similar or knows what might be causing this offset/saturation issue?

Thanks in advance!

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[Esteban Merino]

In the end, I was able to fix it using one of the plugins available for OpenEPHYS, specifically the one called Scale Converter.

Thanks for the help in the previous message, Josh

Best,

El jueves, 26 de marzo de 2026 a las 9:13:12 UTC-7, Josh Siegle escribió:

Hi Esteban,

Do the recorded signals have the same issue? Or do you think this is a display issue?

And have you tried acquiring the two signals with an oscilloscope to see how they differ from what appears in the LFP Viewer? It would be helpful to know what the expected output is.

Best,

Josh

On Wed, Mar 25, 2026 at 5:14 PM, Esteban Merino <emerin...@gmail.com> wrote:

Hi everyone,

I have a question regarding my setup. I am currently sending the analog signal from a treadmill through a coaxial connector to the I/O board, and from there into Open Ephys.

I’m able to visualize the signal in the LFP viewer without issues. However, the direction signal (ADC2) appears highly saturated, and I cannot properly see the scale for that channel. Additionally, the mean of the signal is negative.

Although not shown here, the speed signal (on ADC1) shows a similar issue: it is centered around -5 V and increases from there, but always returns back to -5 V baseline.

I have also plotted the raw signals, and indeed all values sit at around -5 V when the treadmill is not moving.

Has anyone experienced something similar or knows what might be causing this offset/saturation issue?

Thanks in advance!

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[Josh Siegle]

Ok, glad that fixed it! What was the scale you needed to apply?

Josh

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