Tag Archives: RTC
by MIKE BARELA @ adafruit.com:
Trinket lends itself very well to building clock projects, its small and easy to hide behind a larger display. And clocks don’t need a lot of logic, this example only has maybe 20 lines of code. Adding a digital display via I2C is possible using seven segment or character-based displays (with the library code posted for other projects).
This project interfaces Trinket to the the Adafruit DS1307 real-time clock (RTC) breakout board to form a clock. But in a twist, the display is done using two analog meters. One for hours, one for minutes.
The Trinket can output to a meter without digital to analog converters. Trinket has pulse width modulation (PWM) on three of its pins. The meter uses a moving coil inductance movement, acting to average the indication of current flowing through it. If you have narrow pulses, the average voltage it sees is lower, thus the current is lower for the fixed resistance attached to it. For wide pulses, the meter sees nearly the supply voltage and will stay around the full scale. This circuit varies the pulse width sent to the meters proportional to the hour of the day and the minutes after the hour.
Meter Clock using a DS1307 RTC and Trinket Microcontroller – [Link]
by Susan Nordyk @ edn.com:
Furnished in a ceramic surface-mount package that is just 3.2×1.5×0.8 mm, the RV-8803-C7 real-time clock module from Swiss manufacturer Micro Crystal consumes 240 nA and operates from a supply voltage as low as 1.5 V to increase the life of backup supplies. The device gives designers the option to replace expensive batteries and supercapacitors with low-cost multilayer ceramic capacitors for battery backup.
The temperature-compensated real-time clock is accurate to within ±3.0 ppm (±0.26 seconds/day) over a temperature range of -40°C to +85°C. In addition to low current consumption and high accuracy, the RV-8803-C7 has one of the smallest ceramic packages in the industry with an integrated 32.768-Hz quartz crystal. It operates from a supply voltage ranging from 1.5 V to 5.5 V and employs an I2C interface.
Tiny real-time clock consumes only 240 nA – [Link]
Startup Percheron Electronics Ltd is looking to fund their rather neat E-Paper display HAT for the Raspberry Pi. Unlike some similar display solutions for the Pi this E-ink HAT attaches without any long ribbon cables. An advantage of this type of display (similar to those used on the Kindle) is that the image persists on the screen when power is removed so they use less power than a TFT display but the E-Paper technology does not support fast moving images.
The PCB is compliant with the Raspberry Pi Foundation’s HAT specification, including device tree configuration of the required GPIO pins by the HAT EEPROM. The board is able to drive a 2.7″ 264 x 176 pixel E-Paper display panel and is also suitable for the 1.44″ and 2″ display panels from the same manufacturer.
The board also features a DS3231 real time clock (RTC) IC with a CR1220 lithium coin cell for battery backup when the Pi is powered down. The DS3231 is accurate to 5 parts per million, or within 3 minutes per year. The RTC can generate an interrupt/alarm signal and also a 32 KHz clock signal which can be connected through to GPIO pins by solder pad links, if required.
Neat E-ink HAT for RPi – [Link]
The PCA8565 plays a very important role in the real time systems like digital clock, attendance system and tariff switching. In applications where timestamp is needed, PCA8565 real time clock is a good option. It provides the following benefits: low power consumption, allows the main system for time-critical tasks, and more accurate than other methods.
The PCA8565 is a CMOS real time clock and calendar optimized for low power consumption. A programmable clock output, interrupt output and voltage-low detector are also provided. All address and data are transferred serially via a two-line bidirectional I2C-bus with a maximum bus speed of 400kbps. The built-in word address register is incremented automatically after each written or read data byte. It provides a year, month, day, weekday, hours, minutes and seconds based on a 32.768kHz quartz crystal. It features alarm and timer functions, low current, and extended operating temperature range of -40 degrees Celsius to +125 degrees Celsius. It further contains an 8-bit year register that can hold values from 00 to 99 in BCD format, which also compensates for leap years, thus leap year is automatically corrected.
From the application circuit, the PCA8565 can be used to perform standard RTC functions, such as tracking the actual time and date, or acting as a reference timer. To support power management, the PCA8565 can be used to wake the microcontroller from hibernation mode. In systems that use a PLL, it can serve as a system reference clock for the PLL input. The PCA8565 can also be used as a watchdog timer, or as an activation timer to start measurements or initiate other functions.
PCA8565 Application Circuit – [Link]
by Alan @ kalshagar.wikispaces.com:
I found those beautiful vintage IV9 & IV16 tubes and I had to use them, clock being the perfect candidate. I made already mutliple others based on what was supposed to be a WordClock (hence the project name) only, but became more diversified. I did also a first test with a chainable 5cm x 5cm tube board, this is a 5cm x 10cm dual board improved version.
When I made this project and designed it the idea I had was of course the design (very important) but also reusability and pragmaticallity regarding the components used. What I mean by the latest is that you never really know what component you’ll have at hand, depends on your provider, the component availability, it’s price, or even the package DIP or SMD. Hence the board can work with 3 different type of RTC clocks: just use your favorite or the one in your shelf stock. Personally I love the Maxims DS3231 and DS3234 which are temperature compensated (to a fantastic extend for the DS3234), and both are accessed through different protocols: SPI for the DS3234 and TWI for DS3231. There’s also the EPSON RTC4543 for those living in Japan like me. So again depending of what else you need to wire, choose your poison: all the pins of the MCU are accessible and there’s even a small zone for some DIP components.
The top board uses 74HC595 for maintaining the displayed digits: they come very cheap but I didn’t want to be stuck to the DIP or SMD model (having both in stock), so the board can use any of the two. Same goes with the current limiter resistors: SMD, through hole or even resistor array, your pick. And of course there’s a SMD or DIP led footprint under each tube for the blingbling! (single color, not RGB led)
IV9 & IV16 tube numitron clock – [Link]
This project embodies the concept of I2C bus standard. It signifies how important to know the I2C devices and how they will be integrated. There are a lot of innovation can be made using the standard and more people are attracted to get involve in the embedded world professionally or just as hobbyist. The number of I2C devices included in this project may develop new ideas and designs.
The design includes 8-Bit Microchip PIC18F14K22 microcontroller which serves as the master of the I2C bus communication principle. The PCA9547D device is an 8-channel I2C-bus multiplexer with reset that communicates with the I2C devices one at a time. The PCA9500 device is an 8-bit I/O expander with an on-board 2-kbit EEPROM that simplifies the connection of LCD to the multiplexer. The MCP9801-M/MS device is a 2-Wire High-Accuracy Temperature Sensor for temperature monitoring. The 24LC025/ST device is a 2.5V, 2 Kbit Addressable Serial EEPROM (Tape and Reel) with no WP pin for firmware application. The MCP3221A0T-I/OT and TC1321EOATR devices are both for data conversion. The MCP3221A0T-I/OT is a Low Power 12-Bit A/D Converter With I2C Interface and the TC1321EOATR device is a 10-Bit Digital-to-Analog Converter with Two-Wire Interface. The MPL115A1 device is Miniature I2C Digital Barometer for pressure sensing applications. The MCP79400-I/MS is a Battery-Backed I2C™ Real-Time Clock/Calendar with SRAM and Protected EEPROM for applications that includes time. The PCA9530D device is a 2-bit I2C-bus LED SMBus I/O expander optimized for dimming LEDs in 256 discrete steps for Red/Green/Blue (RGB) color mixing and backlight applications. The 2X16 LCD is for display and monitoring application.
The design is very versatile since it opens up ideas to innovate. It is an excellent project for embedded system application. There are a lot of student will be attracted to develop their own design.
Interfacing MCU to various I2C Devices XD – [Link]
John Boxall over at Tronixstuff has posted a detailed tutorial on how to on how to use DS1307 and DS3231 real-time clock modules with Arduino:
There are two main differences between the ICs on the real-time clock modules, which is the accuracy of the time-keeping. The DS1307 used in the first module works very well, however the external temperature can affect the frequency of the oscillator circuit which drives the DS1307’s internal counter.
This may sound like a problem, however will usually result with the clock being off by around five or so minutes per month. The DS3231 is much more accurate, as it has an internal oscillator which isn’t affected by external factors – and thus is accurate down to a few minutes per year at the most. If you have a DS1307 module- don’t feel bad, it’s still a great value board and will serve you well.
Using DS1307 and DS3231 real-time clock modules with Arduino – [Link]
The most popular RTC for the Arduino is the DS1307. However, it does have some drawbacks, the most notable of which is that its operating voltage is 5v, which means it cannot be used with 3.3v projects. The Maxim DS1339 however, features a wide tolerance of voltages from 2.97V-5.5V with the typical voltage as 3.3v, a battery backup, two alarms, and a trickle charger. The breakout board here packages the DS1339 with the components and connections necessary to use with your Arduino projects easily.
MAX DS1339 RTC Real Time Clock for Arduino – [Link]