US Digital

The TTL outputs of our incremental encoders can sink (pull down) less than 4mA and source (pull up) less than 200uA. This is not always adequate. For long cables (6 to 1000 feet) or noisy environments, one of these tiny plug-in driver boards will provide additional drive. They are so small, they fit between the two wire loops on either side of the 5 pins of the encoder as shown in the attached drawings.

The PC4 is an RS-422 cable driver board designed to attach to our older first generation encoders: E2, E3, H1, H3, S1 and S2.  An on-board 0.1uF bypass capacitor across the power pins on each of these boards compensates for inductance and noise which can be expected at the end of a long cable. Each board has a 5-pin socket designed to plug into the 5 pins of the encoder.

A ribbon or discrete wire cable connector can plug into the on-board 10 pin shrouded plug. Simple ribbon cables can be used for lengths up to 100 feet. Twisted pair cable is recommended for longer lengths. An optional terminating resistor may be placed across each pair on the receiver side of the cable as low as 270 Ω, matching the cable's characteristic impedance. When calculating the power requirements of the encoder side of the cable, include the current consumed by the module, the driver IC and any terminating resistors. Be sure to supply sufficient voltage to compensate for the voltage drop across the power and ground wires (round trip). The typical cable resistance for 28 AWG wire is 60 ohms per 1000 feet. If an RS-422 receiver chip such as 26C32 is used on the receiver side of the cable, we recommend a 0.1uF ceramic monolithic bypass capacitor across +5V and ground located within 1 inch of the receiver chip.