The Lutron Smart Bridge Home Kit
Home automation is the dream of many electrical engineers and hobbyists, with the limiting factor typically being the personal budget. While most home automation devices allow control of lights and outlets, the Lutron also allows remote control of blinds and shades.
The Lutron Smart Bridge Home Kit ($88) contains an in-wall dimmer switch, a Pico remote, and the Smart Bridge. This allows the replacement of one wall switch that can control incandescent, fluorescent, and most LED lights. The Lutron SmartBridge allows users to control devices remotely with their smartphone or the included remote.
Image courtesy of Lutron.
The system integrates with Amazon's Alexa, Apple Homekit, Nest, and many others.
The Pico Remote
The Pico remote can control one or many wall switches at a time. It has buttons for on, off, preset, raise and lower to control lights, shades, or some audio systems.
Open the Pico remote by inserting a large flathead screwdriver (or key) into the slot on the side of the remote closest to the bottom button.
The remote control includes a CR2032 battery, several SMD resistors, several SMD capacitors, a crystal oscillator, and a Split Ring printed monopole antenna. The heart of the remote is a Silicon Labs 4010 RF transmitter.
- Built on an 8051 µC
- 4kB RAM (Random Access Memory)
- 8kB NVM (Non-Volatile Memory)
- 128 bit EEPROM (Electrically Erasable Programable Read Only Memory)
- 8 byte low-leakage RAM
- Digital peripherals
- Power characteristics
- High-performance RF transmitter
This tiny transmitter has impressive range and power output of 10 dBm. The sub-GHz transmitter stays well away from the crowded 2.4 GHz band that microwave ovens and Wi-Fi access points compete for and easily penetrates walls for whole-house usability.
It should be possible to link a single transmitter to open your garage door, turn on the garage lights, turn on the exterior lights, and open the blinds throughout your house when you arrive home, all from the comfort of your car. A single remote could also be programmed to turn your entire house off at night or, in an emergency, turn on all lights and open all shades.
Caseta Wireless Bridge
The Caseta Wireless Bridge connects your Lutron devices to your smartphone, Apple Home, or Amazon Alexa, etc. It is a 7 cm x 7 cm x 3 cm white box with an RJ45 connector to connect to your home router, a micro-USB connector for power, and a right angle tactile switch for reset.
Open the Caseta Wireless Bridge by removing the four M2x10mm self-threading screws at the bottom of the unit hidden underneath the four gray stick-on feet with a Torx T8 standard driver. Remove the internal M2x10mm self-threading screw and desolder W1 while pulling up on the board. The internal transparent plastic circuit board holder is attached to the top white plastic box by four melted connections. If you wish to remove the plastic circuit board holder, do so with flush-cutters after you remove the circuit board.
Upon removing the bottom plastic case, we are presented with the bottom of the circuit board. Here the only component of note is U5—the STM32L100—a 32-bit microcontroller with USB, three USARTs, two SPIs, and two I²C communication lines. This capable device could handle many communication and computation tasks.
After desoldering W1 (a helical wire antenna) and flipping the board, there is only a single small microchip outside the RF shielded area—the Texas Instruments CC110L wireless RF transceiver. This sub-gigahertz transceiver has transmit power up to +12 dBm (16 mW) and receive sensitivity as low as -116 dBm (2.5×10-15 W).
The metal cover RF-shield on the front side of the board can be removed without tools. Inside the metal perimeter, in the top left corner is the KSZ8081 Ethernet transceiver which takes care of communication between the Local Area Network and U1, a Texas Instruments AM3352 32-bit microprocessor.
Adjacent to U1 is U10, a serial EEPROM. In the upper-right corner of the metal box is the TPS650250 power management IC. The other two large black chips are from Micron Technologies, and require an online decoder to decipher their identities as SDRAM and NAND flash memory.
The microcontrollers work together to bridge different wired and wireless technologies to allow the Lutron devices to work seamlessly with controls from Apple, Amazon, and others.
|Texas Instruments AM3352BZCE30||TI MPU Sitara ARM Cortex-A8||$13||Datasheet|
|Texas Instruments TPS650250||Power Management IC||$4||Datasheet|
|Microchip KSZ8081RMACA||Ethernet Transceiver||$1||Datasheet|
|STMicroelectronics STM32L100RBT6||32-bit microcontroller||$5||Datasheet|
|Micron MT29F2G08ABBEAH4-IT:E*||NAND Flash Memory||$3||Datasheet|
|Texas Instruments CC110L||Wireless Transceiver||$5||Datasheet|
Lutron 15-Watt Dimmer
Underneath the switchplate cover are two #6-32x5-32" flush head bolts. After removing the bolts, use a small flat-head screwdriver to gently pry the plastic pushbutton housing away from the metal backing plate. Remove the two 2 mm x 12 mm self-threading screws and use a center drill to defeat the security rivet. The metal plate can be set aside to reveal the contents of the switch housing. Slice through the stickers on either side of the housing at the mating of the top and bottom pieces.
Inside the switch-housing is a friction-fitted circuit board that does not remove easily due to the presence of a metal clip at the lower right corner of the circuit board that is press fitted into the back of the switch housing. I recommend desoldering that component from the circuit board to avoid damage.
On the front of the board are various LEDs, transistors, switches, resistors, current-sense resistors, capacitors, a crystal, a loop antenna (which is oriented toward the camera and thus difficult to see), and Q1, a TO-220-package device labeled "130355 NXP PJA1537 D6 0728" that might be a high-power transistor.
On the reverse is where most of the interesting circuitry is located.
In the upper right corner, you'll see where I damaged the circuit board upon removal. The large microcontroller is the STM8L151, an 8-bit 16 MHz processor that controls the circuit board and communicates with the TICC110L transceiver. Additionally, there is a rectifier and two STN1NK80Z N-channel MOSFETs.
The board is further populated by power control circuitry and various other passive components.
|STMicroelectronics STM8L151C8U6||8-Bit Microcontroller||$2||Datasheet|
|Texas Instruments CC110L||Wireless Transceiver||$5||Datasheet|
|STMicroelectronics STN1NK80Z||N-Channel MOSFET||$2||Datasheet|
|Power Integrations LNK562DN-TL||Off-Line Switcher IC (for transformer replacement)||$0.4||Datasheet|
A great deal of good engineering went into making the Lutron Wireless products, and even more went into the Lutron Smart Bridge to make it compatible with various competing standards.
If you want to "hack" the controllers to create your own Lutron-compatible products, the place to start appears to be with the CC110L transceiver. However, you should stay away from creating high-voltage appliances and focus on the low-voltage side of things—e.g., blinds, garage-door openers—as there is no way to safely engineer your own RF power line switches.
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