Kaylee is a RS-485 adapter for the imp001; the UART on pins 1 and 2 is connected to an ST485 Differential Driver, which translates between the imp001’s 3.3V single-line UART signals and a ±5V differential signal for RS-485 devices. Kaylee’s design was motivated by many industrial devices and appliances that communicate point-to-point or in small networks using RS-485.
Kaylee is powered by a 12V supply, either provided on pin 4 of the optional RJ-12 registered jack connector (J4) or by the optional barrel jack (J2). The power supply is selected during fabrication by placing a solder bead on short pads W1 or W2; the power supply can be re-selected later by removing the solder bead from one set of short pads and placing a bead on the other set. Short pads W1 connect power from the RJ-12 jack, and pads W2 connect power from the barrel jack. Reverse-voltage protection in either case is provided by PFET Q1. Kaylee has an on-board buck power supply built around the TPS62172 to provide a stable 3.3V supply for the imp, and uses an AP1117Y50G-13 fixed 5V LDO to provide a 5V supply for the ST485.
Kaylee’s mechanical design is tailored to fit the Hammond 1593KBK enclosure.
In addition to handling translation to RS-485, Kaylee is very useful for other differential 5V serial communication applications, notably DMX512, commonly used in theatrical lighting. Example code is provided below for a DMX512 application.
Revision-controlled example firmware for the Kaylee board is available on the Electric Imp GitHub examples page.