Data Sheet

When the RC signal on the SEL channel is lost or invalid, the optional FAILMODE jumper determines

the output behavior. If the jumper is left off, the master inputs will be in control. If the jumper is

connected, the output channels go low and stay low for as long as the signal on the SEL channel

remains invalid. For many servos and electronic speed controls (ESCs), a constant low on the signal

line will turn them off, which might be desirable if the control signals are known to be bad.

Note that SEL is the only input that requires a valid RC servo signal (10–330 Hz pulse rate, 0.5–2.5

ms pulse width); the master and slave inputs can be general digital signals. For example, you could

use OUT4 to control the brightness of a small (< 20 mA) LED by sending PWM signals to the inputs

on S4 and M4.

Power

The power supplied by the master RC device should be between 2.5 and 16 V, and it must be capable

of supplying the current that the servos connected to the outputs draw. The power pins of the SEL,

M1–M4, and OUT1–OUT4 channels are all connected to the same VM rail, and the board draws its

power from those pins. The power pins of the S1–S4 inputs are connected to each other on the VS

rail but are not used by the board.

Additional outputs and indicator LED

The yellow indicator LED indicates what state the switch is in. The LED behavior is described in

Section 8.

The FAILMODE jumper consists of two pins that might be individually useful to advanced users:

• The FAILMODE pin with the octagonal pad (the one closer to the edge of the board) is the

GOOD output. This output is low when signal on the SEL input is valid, and high when the

signal on the SEL input is invalid or missing.

• The other FAILMODE pin is the EN input. This input is pulled low by default. When this input

is driven high, it disables all of the output channels, causing them to go low (0 V) and stay

low.

The RC multiplexer has an internal signal named OUT that indicates whether the switch is activated or

not. The OUT signal is high when the switch is active and is low otherwise. This signal is not accessible

on any through-hole pin but you can access it by finding the 16-pin chip and soldering a wire to the pin

1, which is the pin that is closest to the OUT1 channel.

When high, all the output signals on the device will output a voltage approximately equal to 5 V or

VM, whichever is lower. When low, these outputs will be at 0 V (ground). These outputs do not have

resistors in series with them. Each output can source or sink up to 25 mA.

6. Pololu 4-Channel RC Servo Multiplexer Page 33 of 45