Knowledge Base

SL100: Onboard counter type A (OBCA)

The board incorporates an onboard counter type A (called OBCA). This is a high speed hardware counter that can be used for frequency or totalized counting. Typical applications include mains (line voltage) frequency measurement, engine RPM, belt speed (using a pulse encoder) or wind speed using a rotating vane anemometer.

The OBCA exists on several SPLat boards. Generic documentation for the feature is provided in the Onboard counter type A guide.

The OBCA is connected to input number 7. There is some input filtering that limits the maximum count frequency. The maximum count frequency, assuming a squarewave input, depends on the supply voltage to the board. At 10V it is 7kHz, and it increases with supply voltage to 18kHz at 24V supply. The accuracy is approximately 0.1% (this varies from product to product, depending on whether they use a crystal for timing or not. This board has a crystal).