Connecting open-collector outputs

Introduction

An open-collector output is a transistor whose collector is not connected to other internal circuits, while its emitter is connected to the common rail. The transistor operates as a switch controlled by the preceding circuit. The off state (cutoff) corresponds to logic 1; the on state (saturation) corresponds to logic 0.

An open-collector output can increase the allowable digital-output current and directly switch a low-power load. An external resistor pulls the output up to an external supply, allowing devices with different operating-voltage levels to communicate.

Connection rules

To generate a signal, connect the open-collector output to a supply through an external pull-up resistor, typically several hundred ohms. Select the resistance for the required switching speed and power consumption. Lower resistance increases speed and power consumption.

Paralleling open-collector outputs to control a higher-power load. The transistor's off-state resistance is high but not infinite, so a small leakage current still flows.

Connecting to a Wiren Board controller

Three connection methods are available:

1. WBIO-DI-WD-14, 14 channels: connect the open-collector output to a Dx terminal and the device ground to the module's iGND.
2. WBE2-DI-DR-3, 3 channels: connect the output to the Ox terminal corresponding to the expansion module and the device ground to the controller GND.
3. Controller Ax (D1): add an external pull-up resistor of approximately 10 kΩ between 5Vout and the corresponding Ax terminal. Join the device and controller grounds.

Example: WBIO-DI-WD-14

Other Wiren Board digital-input modules are connected similarly.

1. Connect the device ground to iGND and the open-collector output to Dx. The module inputs are galvanically isolated from the controller, so the connected device and controller may have separate grounds.
2. Apply power, start the controller and open its web interface.
3. Add the module to the controller configuration.
4. Check that the external module appears in the web interface.

Web-interface controls

For the internal three-channel module, follow the WBE2-DI-DR-3 installation and configuration instructions.