Reference design beverage coaster

Renesas and TE Connectivity: Reference design beverage coaster

We are excited to debut a practical reference design in celebration of Oktoberfest 2017! Renesas and TE Connectivity have joined forces to bring you an exclusive beverage coaster that lights up, plays music, and indicates beverage drinkability!

The Oktoberfest coaster is a self-contained PCB board inside a plastic casing to protect it from accidental spills and overflowing foam. The coaster features a Renesas Synergy™ MCU using the Synergy Software Package (SSP), and multiple power/analog components from the Renesas product line. There are also five RGB LEDs and an ambient light sensor on the top.

As a beverage approaches the coaster center, the LEDs blink with increasing frequency until the drink is set down on top. A TE Connectivity thermistor indicates if your beverage is too warm (flashes red) or just right (flashes blue) while “The Chicken Dance” plays in the background. Simply press the switch on the back of the coaster to turn the board on or off.

The Reference Design:

  • Detects beverage proximity; LEDs flash
  • Detects beverage placement; LEDs solid & song plays
  • Indicates beverage drinkability
  • Utilizes low power consumption
  • Low continuous active current with on/off switch
  • Powered with two AAA batteries
  • Quickly designed utilizing SSP’s Application Programming Interface (API)
coaster circuit board
Front of Beverage Coaster PCB
coaster board, circuit boar and batteries

Back of Beverage Coaster PCB

Product Description
ISL8202MIRZ-T7A Analog 3A single, DC/DC Power Module, 4.5x7.5mm QFN, 250pc Reel
ISL29102IROZ-T7A ISL29102IROZ PbFree Small, Low Power, Voltage-Output Ambient Light Photo Detect IC
ISL9111EHADJZ-T7A Low Input Voltage PWM/PFM Step Up Regulator, Adj V, 6LD SOT23, 250pc T&R
ISL28133FHZ-T7A ISL28133FHZ Pb-Free Micropower, Precision 5V CMOS Oper. Amplifier, 250pc Reel
ISL28534FVZ-T7A ISL28534FVZ Pb-Free 5V Instrumentation, Zero-Drift, Prog Op-Amp, 250pc T&R
ISL21440IRTZ ISL21440IRTZ Pb-Free, Micro-Power FGA Reference w/ Comparator (2V-11V)
R7FS3A77C3A01CFM#AA1 ARM® Cortex®-M4 Synergy S3 Microcontroller IC 32-Bit 48MHz 1MB (1M x 8) FLASH 64-LFQFP (10x10)
YSDKS3A7E20 Synergy DK-S3A7
YIOTFASTPROTOS3A7 Synergy S3A7 IoT Fast Prototyping Kit
GA10K3A1B TE Connectivity Thermistor Sensor
5-146285-2 TE Connectivity Unshrouded 2 Position 2.54mm Thru-Hold Connector Header
5-146285-3 TE Connectivity Unshrouded 3 Position 2.54mm Thru-Hold Connector Header
Renesas, circuit board

Technical Highlights: The beverage coaster reference design showcases Synergy MCU from the S3A7 MCU Group with the ISL8202M 3A power module and several other power and analog signal chain components. The board utilizes the ISL9111 boost converter to use all available power from two AAA batteries and increase the voltage to 4V. The ISL8202M bucks the voltage down to 3.3V for the rest of the components on the board. Additionally, the board uses a TE GA10K3A1B thermistor, ISL29102 light to voltage sensor, ISL28133 MicroPower zero-drift op-amp, and ISL28534 programmable gain zero-drift in-amp.

Microcontroller: The Synergy S3A7 Group MCU device is powered at 3.3V and the internal oscillator is utilized to minimize component count. It controls each color in the RGB LEDs and can produce any color of the rainbow by changing the duty cycle of each RGB control line. For this demo tool, the LEDs are set to either blue, purple or red to indicate relative beverage temperature. The S3A7 MCU also plays a song when the beverage is placed on the coaster. Song notes are generated by driving the piezoelectric buzzer with square-wave digital signals produced by utilizing the flexible internal timers in the S3 to produce unique frequencies for each note, duration and beat.

The SSP C-code running on the S3A7 MCU was written using the e2studio development environment, an intuitive development tool. The simple click-through configuration capability of the tool coupled with simple API calls to the SSP deliver an abundance of time-saving benefits to make designing with the Synergy Platform quick and easy.

The Synergy Platform allows the RTOS, middleware, communication stacks, user interface, and detailed MCU functions to be accessed entirely through the API. Developers can immediately start developing end-product application code at the API level, thus eliminating the learning curve for software and MCU operation below the API. In this design, the following S3A7 MCU hardware features were utilized using simple API calls:

  1. Timers – the abundance of timers in the MCU are used to create the musical notes, control the ADC and to create the RGB LED PWM control.
  2. A/D converter – the MCU’s ADC is used for the light to voltage sensor.
  3. Easy setup of the interrupt control drivers to detect external signals and control the GPIOs.

Debugging from within e2studio is simple and intuitive. With the addition of the low-cost SEGGER Synergy J-Link® Lite for Synergy hardware debugger, the code in the Beverage Coaster can be modified or additional functionality added.

renesas, IT, circuit board

DC/DC switching regulators: The ISL8202M produces the 3.3V rail that is used by the rest of the active components on the board. This power module features a power dense design with minimal external components, providing a simple design with the ability to deliver a lot of power in a small space. While the ISL8202M is capable of delivering up to 3A of output current, this design actually draws less than 50mA on the 3.3V rail during song-play. This low-current application shows off the Pulse Frequency Modulation (PFM) mode of the ISL8202M which greatly improves the efficiency at light loads.

Circuit board, light applications

The ISL9111 boost converter is up to 97% efficient with a low quiescent current of only 20uA, making it ideal for light load applications using alkaline, NiCd, or NiMH batteries. It can deliver 100mA with a Vin of 0.9V or 240mA from 1.8V in. This converter ensures all the power is used from the two AA batteries on the board.

Circuit board, low battery detect

Low Battery Detect: The low battery detect of the coaster is not implemented but is a viable addition for the DIY enthusiast. When the batteries near their discharge state, a low battery detect circuit alerts the user that it is time to change the batteries. This is indicated by the D4 LED flashing red color. The circuit uses the ISL21440 voltage reference plus comparator, consuming only 400nA typical quiescent current. The battery voltage is divided down and compared to the 1.182V output of the reference. If the battery voltage drops below 2.2V, the output of the comparator goes HIGH and the microcontroller commands the D4 LED to flash red. This feature can most easily be demonstrated by removing the batteries and powering the board with a programmable power supply set below 2.2V.

Circuit board, thermistor

Temperature Measurement: The temperature of the beverage resting on the coaster is sensed by the GA10K3A1B TE Connectivity thermistor. It is encapsulated in a thermally conductive epoxy coating and has a wide operating temperature range as well as a fast response time. The lead wires are made of alloy for reduced thermal conductivity, thereby reducing the stem effect and providing high stability and reliability. The voltage across the thermistor is conditioned by the ISL28133 zero-drift operational amplifier before being passed on to the MCU. The op-amp is very accurate over temperature (0.075uV/°C max), has very low offset voltage and noise, and only consumes 18uA typical supply current.

coaster connectors

Board Connectors: The 5-146285-2 two-pin header with gold plating provides the connection for the microcontroller reset function. With 100mil spacing, a regular jumper connector can be used to connect the reset pin to the board’s ground, thereby resetting the MCU. Two 5-146285-3 three-pin headers are used on the coaster to connect the pushbutton switch board to the rest of the board. The switch is used to turn power to the board on and off and needs to be raised off the main board in order to reach the outside of the enclosure. The 5-146285-3 provides the necessary elevation and sturdiness for the switch board, and also conducts the current from the batteries and to the rest of the board via the middle pin on each side.

Circuit board

Strain Gauge: The strain gauge feature of the coaster is not implemented but is also a viable addition for the DIY enthusiast. The gauge would be part of a Wheatstone Bridge to detect the weight of the drink, have the signal amplified by the SL28534 instrumentation amplifier, and sent to the MCU for analysis. Programmable to 9 different gain settings, the in-amp offers flexibility as well as precision. It is built with zero-drift amplifiers to provide excellent accuracy over temperature, has a high CMRR, low offset voltage, low noise, and low gain error.

coaster circuit board

Ambient Light Sensor: The coaster board is populated with the ISL29102 light to voltage sensor. This sensor detects the decrease in ambient light as a drink is being placed on the coaster. As the ambient light decreases, the LEDs blink faster and faster until they are fully lit and the song plays. The ISL29102 has an extended light input dynamic range while maintaining excellent sensitivity in dim conditions with low lux levels.

coaster circuit board

LEDs: The LEDs used on this board are ASMB-MTB0-0A3A2 tri-color LEDs. Each LED package actually contains a red, green and blue LED. A different value of pull-up resistor was chosen for each color in order to create an equal light intensity out of each color. The S3 Synergy microcontroller has control over each color and can therefore produce any color of the rainbow by changing the duty cycle of each RGB control line. For the reference design, the LEDs blink based on the ambient light and change color based on the temperature of the beverage placed on the coaster.

coaster circuit board buzzer

Buzzer: The notes of the song are generated by driving the piezoelectric buzzer with a square-wave digital signal out of the microcontroller at frequencies corresponding to each note.

Renesas and TE Connectivity

Reference Design Beverage Coaster

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Octoberfest, lighting beverage coaster

Oktoberfest Coaster