Analog m-pod

‍Introduction

‍Analog m-pod is different from other m-pod models: The other models typically have 8 or 16 physical output lines; a signal is indicated when the voltage on one of these lines alternates between 0 and 5 volts.

‍Analog m-pod has a single physical output line. The voltage level that it produces is determined by three options:

Voltage Range. The factory default is for Analog m-pod to produce output between 0 and 1 volt. The maximum is 0 to 10 volts. You can change the output range in increments of 1 volt.
Voltage Levels. When in Fixed Delta analog mode (see below), Analog m-pod can divide the voltage range into 8 or 16 levels. The idea is to overcome the limitation of having a single physical line so you can have richer information. When in Binary mode (also see below), the voltage range can have up to 255 different levels.
Analog Mode. This determines how Analog m-pod creates the voltage levels.

‍Analog Modes

‍Analog m-pod offers two modes: Fixed Delta and Binary.

‍Fixed Delta mode is simpler: m-pod divides the voltage range by the number of levels. For example, with 8 levels and a 0 to 10 volts range, the output is:

Bit 0: 1.25V (that’s 10 volts divided by 8)
Bit 1: 2.5V (the value of Bit 0 multiplied by 2)
Bit 2: 3.75V
Bit 3: 5V
Bit 4: 6.25V
Bit 5: 7.5V
Bit 6: 8.75V
Bit 7: 10V (the value of Bit 0 multiplied by 8)

‍The main advantage of Fixed Delta mode is that it makes data analysis easier. You have only 8 (or 16) evenly distributed voltage levels to interpret. The disadvantage is that bits cannot be combined: the output will always be that of the most significant bit; any lower bits are ignored. For example, if you send a command to Analog m-pod to activate bits 6 and 7 at the same time, the output will be 10V (bit 7).

‍Binary mode is more powerful but might make analyzing the data more difficult. With a 0 to 10 volts range, the output is:

Bit 0: 0.04V (the value of Bit 1 divided by 2)
Bit 1: 0.08V (the value of Bit 2 divided by 2)
Bit 2: 0.16V
Bit 3: 0.31V
Bit 4: 0.63V
Bit 5: 1.25V
Bit 6: 2.5V (the value of Bit 7 divided by 2)
Bit 7: 5V

‍The advantage of binary mode is that bits can be combined. You can have up to 256 different voltage levels. For example, if you send a command to Analog m-pod to activate bits 6 and 7 at the same time, the output will be 7.5V (2.5V + 5V).

‍Tips

‍Consider setting Analog m-pod to use “Single Pulse” mode instead of the default “Reflective” mode. This will reduce odds that two different signals will overlap.

‍If you want to use Binary mode, we recommend a couple of steps to reduce the total number of voltage levels, which would make data analysis easier:

If you are using a Riponda or RB Series response pad with StimTracker, map all the response pad keys to a single output pin (voltage level). This will give you the precise onset. You can always determine which key was pressed from the behavioral data file generated by SuperLab or other stimulus presentation software you are using.
If using StimTracker, map the Audio Left and Audio Right signals to a single output pin (voltage level).
Generally, try to reduce the number of voltage levels if your experimental design permits.

‍If using Fixed Delta mode, we recommend that bits marking the onset of stimuli be lower than bits indicating a participant response. For example, if marking the onset of visual stimuli using a light sensor, it is better to have that indicated by Bit 0 instead of Bit 7. In a typical trial, stimuli are always presented first.

‍Default Output and How to Change It

‍The factory default for Analog m-pod is to produce output only in response to commands sent via USB to StimTracker or the response pad.

‍In order to produce other types of output, e.g. in response to onset of light sensor or audio, Cedrus provides a free utility for configuring your m-pod. After you use it, your configuration is saved to flash memory so that it’s remembered even after you power off m-pod.

‍

Back to m-pod Support main page
Last Revision: Dec 8, 2022