The Opal (and Emerald and Sapphire) movement monitor has a single button input that can be used to "tag" or "mark" the Opal data stream. Often it's used to mark the start and end of a gait and balance test, or to precisely record external events. Although the External Synchronization Interface on the Access Point is meant for this, sometime you just really need it on the Opal itself -- particular when using the logging modes of operation.
How the button "input" works
The Opals have a 10 pin connector that is used to charge the Opal and transfer data to the Dock. One of those pins is the button input. Usually it's weakly pulled high (to a "1"). If you short that pin to ground, the Opal records a "0" for each sample of data collection. Otherwise, it records a "1". It's as simple as that. Pin 2 is the button input, and Pin 6 is ground, so if you just short pin 2 to pin 6, you've pushed the button. Here's the schematic:
Since you're just grounding Pin 2, you could also replace the switch with an N-channel MOSFET, or even an opto-islated FET (like the HFE411) to trigger the Opal button.
See the "Working with HDF" section in the Technical Guide for information about how the button state is stored in the data stream.
Making your own button
The connector on the Opal PCB is the Hirose ST60-10. Datasheet for that family of connectors is here. There are two connectors that mate to this connector: the Hirose ST80X-10S (Digi-Key # H1957CT-ND), which is a vertical "docking" connector, and the ST40-10S-CV (Digi-Key #H11360-ND), which is meant for a 4mm OD maximum 10 wire cable. We suggest using the ST40-10S-CV, and soldering directly to pins 2 and 6. Use the plastic cable shell that comes with the ST40-10S-CV in order to lock into the Opal connector, and of course strain relieve the cables.
Closeup of the Opal Connector
The Hirose ST40-10S-CV connector set (connector + shell).
The assembled Hirose ST40-10S-CV connector.
Opal for scale
Off the shelf solutions from APDM, Inc.
NOTE: We no longer manufacture these options, but they are left here for reference
APDM has two button options for you to choose from.
1. The Opal External Button, which uses the Hirose ST80X-10S vertical connector soldered to a very thin PCB, with a small surface mount tactile button on the outside.
Opal external button
Opal with external button.
2. The Opal external button breakout board, which uses just the connector part of the ST40-10S-CV and a small PCB that has two holes for you to solder a wire directly top.
The button breakout board. Note the "BTN" and "GND" connections for wiring in an external button. The "5V" connection is to charge the opal, not to provide 5V power.
Opal with the button breakout connector (note that the entire PCB fits inside the Hirose shell)