Last article, I wrote about how to use our own homemade Arduino Pro Mini bare bones along with an OLED display and how to make both of them consume as little power as possible. In fact, we managed to achieve a small 1.1 uA current with both of them sleeping. Also in our circuit there were a PCF8563 real-time clock module and one AT24C64 EEPROM memory. Now, to proceed with our smartwatch project we need to add sensors, such as an accelerometer, compass and pressure sensor. This article is about how to add them, read the variables and keep saving power.
On the previous article I wrote about how to use the real-time clock module with the EEPROM non-volatile memory. Now it is time to get something working that resembles a watch. Make something that matters. How about adding a display? Last post it was possible to achieve a power consumption of only
16 uA (improved) 0.7uA on the smartwatch prototype. Now we can see how much power the watch will consume. In this case, it is an application that needs to consume the smallest current possible but also needs a display, then one can use a OLED display, which is the abbreviation of “Organic Light-Emitting Diode”, which is a much more economic display in terms of current than the regular LED displays. An overview about OLEDs, first.
One thing I didn’t find clearly over the internet is how to make an Arduino Pro Mini bare bones, that is, from the scratch, and how to make one on the breadboard. This is really useful if you want to make a custom pcb/smd circuit, because you will be able to test your hardware ans software before sending the schematics and the layout of the board to the manufacturer. Also, it will make your circuit Arduino compatible. If you read my previous article, here, I showed how to make a simple circuit with the PCF8563 real-time clock, reading and writing it. Now it is time to put your Atmega 328p on the breadboard and complete a simple read of the clock, maintaining the power consumption low, and for that I will use the LowPower library.
Last post I started a discussion about some of the most common real-time clocks out there, and people gave some feedback to update the article. At the end, I chose the PCF8563 from NXP to use on the first smd version of my smartwatch (Arduino compatible). Of course all RTCs are fairly accurate, some more than the others, and as we’ve seen, from 2 to 20 ppm, but the real deal for this project was to use a module that consumes the least power possible, and on this IC is from 0.5uA (standby) to 200uA (I2C interface active).
Well, this is my very first post on this blog. First of all, let me introduce myself. I’m a Brazilian engineer graduated in mechatronics in a university called USP (or University of São Paulo). I don’t expect for you to know it, but for people that works in academics, it is a well known university, that was ranked 39º best of the world on the year 2009. However, English is not my primary language, because here we speak Portuguese. So expect some spelling mistakes.
On this first post, I’m going to describe some of the RTC modules available on the market, and how to use them. The advantages and disadvantages about each other and also their usage to make one of my projects, that is an arduino based smartwatch, with accelerometers, compass, altitude and pressure sensor. For this purpose, I had to search for the module with the least power consumption possible. For most of this I have to thank Dennis, another member on Instructable that helped me on my first steps with RTCs.