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Biamp Systems

Wiring potentiometers to the EX-LOGIC and GPIO

Of the many options that can be used to control levels in Tesira, one allows the use of external potentiometers. Since potentiometers are analog devices, these need to be connected to Tesira through GPIO ports or an EX-Logic. This note covers the details on wiring off-the-shelf potentiometers as well as Biamp’s RP-L1 and RP-L2 Remote Panels to GPIO ports 1-4 or to ports 13-16 of the EX-Logic. Ports 1-12 of the EX-Logic do not support Control Voltage. 

Wiring a generic potentiometer

Wiring a potentiometer to a GPIO or EX-Logic can be a bit confusing since it has three contact points. Not wiring it properly might cause the potentiometer to either work in reverse or not at all. Looking at the pot from the knob side with the contact points pointing at you, you will have the Low or CCW (Counter Clockwise) terminal on the left, the W (Wiper) terminal in the middle and the High or CW (Clockwise) terminal on the right. Connect the CCW terminal to the Ground terminal, the W terminal to the analog input and the CW terminal to the +5V terminal of the EX-Logic as shown in the diagram below.

A linear-taper potentiometer in the 5K – 50K range is recommended. When the Tesira control voltage port calibration wizard (in Device Maintenance) is run it will sense the voltage range passed by the potentiometer. Note that if a logarithmic (audio-tapered) potentiometer is used, the control will not seem to work “evenly” across the range.

The inputs do have noise filtering but for longer cable runs, lower-value potentiometers in the 5K-10K range will have greater noise immunity. 

Potentiometer to EX-Logic.GIF

Wiring the RP-L1 or RP-L2

The Biamp RP-L1 and RP-L2 are wall plates with 25KΩ linear taper potentiometers for volume control. The RP-L1 has only one potentiometer while the RP-L2 has two. These potentiometers came prewired from the factory with pigtails for ease of installation. These pigtails are color coded green for Low or CCW (Counter Clockwise) terminal, red for W (Wiper) terminal and white for High or CW (Clockwise) terminal. Connect the CCW (green) wire to the Ground terminal, the W (red) wire to the analog input and the CW (white) wire to the +5V terminal as shown in the diagram below.

RPL-x to EX-Logic.GIF

Please note that the RP-L1 and RP-L2 products have been discontinued as of Fall 2015.

Programming

Within Tesira software a Control Voltage block needs to be added to the layout from the Logic objects menu.

The block can be set to Fixed in Unit = True in the Properties of the Control Voltage block to manually assign a specific device and GPIO port to the control, otherwise the compiler will assign one automatically.

Double-clicking the Control Voltage block opens a dialog box to associate controls with the potentiometer. (Note that the Identifier column shows generic names and not the physical port assigned, it can be renamed as desired.) Click in either the Object Code or Instance Tag field to select the desired pairing. (Tip: Left-click once on whichever control you are looking to pair and look at the lower left-hand corner of the Tesira software window to see the Instance Tag of that block.) Finally, choose the Control ID of the channel within the block you wish the potentiometer to control.

Calibration

To calibrate a potentiometer you first need to send a configuration to set the GPIO port as a Control Voltage port. Connect the potentiometer as explained in the wiring sections of this article. 

Once the unit is configured go offline, open Device Maintenance, and select the hardware device which has been configured for Control Voltage.

  • For a Server-class device select the unit in the Device List, then click the Port Settings button and click "Calibrate Control Voltage..." to select the port.
  • For an expander-class device (EX-Logic) click "Remote Devices...", select the desired unit and click "Calibrate..."

Click on the desired port (unconfigured ports will be unavailable to select) to start setup and follow the prompts. First turn to the potentiometer to Maximum and click Next, then rotate to Minimum and press Next, then Finish. The potentiometer will now control the associated level from its lowest to highest setting as defined by the range in the targeted control block.

Further reading

  • All potentiometers that are connected to an EX-Logic or GPIO port must be calibrated to ensure proper operation. See the Tesira software help file for more information.
  • EX-LOGIC programming
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