Data Sheet

7. Functional Description

This section documents the functions and behavior of the RC switch. The information in this section is

not needed to use the device, but it might be helpful if you are curious about the details.

Timing accuracy

The timing accuracy of the RC switch is limited by its internal clock, which has an accuracy of ±2%.

Because of this, the threshold and other timing parameters might vary by a few percent.

Configuration parameters

The device stores two user-settable configuration parameters: threshold and inversion.

The threshold parameter is a pulse width that can range from 900 to 2100 μs and must be a multiple

of 16 μs. The default threshold is 1696 μs.

The inversion parameter can either be enabled or disabled. When inversion is disabled, the pulses

have to be above the threshold in order to activate the switch. When inversion is enabled, the pulses

have to be below the threshold in order to activate the switch. By default, inversion is disabled.

Pulse measuring

The device measures standard RC pulses on its RC input (which is labeled RC IN or SEL depending

on the device). It is designed to have strict requirements for the signal and to deactivate itself as soon

as possible when those requirements are not met. The device expects the pulses to have a width

within 500 to 2500 μs and a frequency within 10 to 333 Hz. These limits cannot be strictly enforced

because of the ±2% clock accuracy, but the device is designed to accept any signal that is within these

limits. If there has been no activity for 130 ms, the signal is considered to be bad. If there have been

too many glitches detected on the RC input, the signal is considered to be bad.

The device requires three good pulses in a row before it will consider the signal to be good. However,

as soon as the signal violates any of the rules above, it will consider the signal to be bad and

deactivate the switch.

When comparing the measured pulse width to the threshold to determine whether the pulses are

above or below the threshold, the device uses a hysteresis of ±64μs.

Safe-start

All of the RC switches except the Pololu 4-Channel RC Servo Multiplexer have a safe-start feature that

reduces the likelihood of unexpected activation. Safe-start mode is active at power up, and while the

safe-start mode is active, the switch does not activate. The device deactivates safe-start mode when

the signal is good and it receives a pulse in the off position. The device will re-activate safe-start mode

if the signal is bad continuously for 500 ms.

7. Functional Description Page 37 of 45