Birch Interface Users Manual

Information in this manual is up to date at the time of writing, but the user interface for this device is evolving as new features are being added, so please check back on our website from time to time.

And, as always: Please reach out to us if you have any questions by email at or by phone at +1 215-387-5456.


The Birch interface is a powerful new optoelectronic interface based on our venerable FIU-932 interface, with an added single board computer and touchscreen for improved ease of use and new capabilities. It can be substituted in any system for a 932 (though support for some older legacy devices is not yet implemented).

The basic role of this interface is the same as it was for its predecessors: it sends light out to the fiber-optic response devices, detects the light received back from them, and converts these signals into standard USB HID computer protocols. Unlike our earlier models, though, Birch has powerful logging and timing capabilities: it can act as a parallel recorder of subject response events, capturing button presses with 5 microsecond resolution at the same time that your psychometric software is presenting stimuli and recording responses. Events are logged to a thumbdrive for later validation of events as they were captured by the "stim" computer.


Bottom view of the Birch interface connectors:


Left side of Birch interface:


User Interface

This is what the screen will look like during typical response collection, with an eight button bimanual response device connected as an example:



Please begin by mounting the Birch interface on a stand so that cables can "flow" downwards. Then connect the power supply (to P6 below) and press the power button (SW1), just to the left of the power supply input:


The system will take about 30 seconds to boot up after the power button is pressed. It is ready to use when you see a screen like this:


You will note that most of the screen is greyed-out: this is to guide the process so that you begin by choosing the response device to use. It is best (and simplest) to connect the removabel and the reposne device first, and then tap in the response device area on the screen and choose "Automatically" from the dropdown.

Connect the optical bundle and response device

Always connect the optical bundle and the response device before putting the interface into an operating mode -- this order is important because the interface will "look" at the optical connections when it is put into a user mode so you want to have the components in place then.


First choose the response device by tapping in this area, and then choose Autoconfigure:

select_response_dev.png automatically.png

The device will be detected (by sending light to it and detecting the unique pattern of light received back from it): if the detected device matches the one you have connected, confirm it.

Second, choose the output mode you want:

select_output_mode.png hid_key_bygrt.png

At this point you can begin collecting subject responses from the USB port.

You will notice the log file area is still greyed-out: insert a writeable thumbdrive in the top left USB slots to enable logging. Data will be written to a file with a date-time formatted filename.

Adapting scripts from older interfaces

If your scripts look for a specific interface unit (e.g., a 932 interface or a 905 interface) they will need to be adapted to find BIRCH-OIU instead. But it might be better to have your script look for Current Designs devices instead, so that they can work with any of our interface units. That is, it might be advisable to search for the Current Designs Vendor ID rather than the interface unit product ID.


Updating is done through a wifi connection and is described in UpdatingBirch.

Legacy Device Support

By "legacy" we are referring to response devices with model numbers beginning with "HH-", as distinct from "HHSC-" devices. These devices were made in 2008 or before. We do not have plans to support them on Birch at this time.

If you have a legacy device for which you need support urgently please email us ( We may be able to help you quickly.


  Specification Value Notes
1. Model Number BIRCH-OIU  
2. Dimensions, overall 9" wide x 6.5" tall x 2" thick without stand or power supply
3. Weight 1 lb 14 oz  
4. Power 5 VDC @ 3A max  
5. USB vendor:product 0x181b:0x0015 Current Designs, Inc.:BIRCH-OIU

-- BenDugan - 18 Apr 2023
Topic attachments
I Attachment Action Size Date Who Comment
automatically.pngpng automatically.png manage 73 K 18 Apr 2023 - 14:35 BenDugan  
birch_connections.svgsvg birch_connections.svg manage 44 K 18 Apr 2023 - 14:40 BenDugan  
birch_side_connections.svgsvg birch_side_connections.svg manage 11 K 18 Apr 2023 - 14:40 BenDugan  
hid_key_bygrt.pngpng hid_key_bygrt.png manage 50 K 18 Apr 2023 - 14:37 BenDugan  
screen0002.pngpng screen0002.png manage 125 K 18 Apr 2023 - 14:42 BenDugan  
screen_normal.pngpng screen_normal.png manage 66 K 18 Apr 2023 - 14:38 BenDugan  
select_output_mode.pngpng select_output_mode.png manage 63 K 18 Apr 2023 - 14:38 BenDugan  
select_response_dev.pngpng select_response_dev.png manage 123 K 18 Apr 2023 - 14:39 BenDugan  
Topic revision: r2 - 05 Sep 2023, BenDugan
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