UPDATED: DS1307 Library

The functions were moved to separate files in the DS1307tiny library.

The sample code in the ds1307tiny_test1 module looks cleaner now. The output should be something like this …

Note that one of the challenges working with a real-time clock the the DS1307 is to set it up with the correct time at the beginning.

• One way is to do that programmatically – write a program for the microcontroller that will set the clock to specific date & time and run that program right at the specified in the code date & time.
• Another way of doing taht is to use some sort of USB-to-I2C module and set the date & time from the computer. Such modules exist but they are kind of expensive for the simeple thing they do.
  Ref: http://www.ebay.com/sch/i.html?LH_BIN=1&_nkw=USB+to+I2C&_sop=15

References

Source code available at: https://bitbucket.org/tinusaur/ds1307tiny

More information about the library will be available at its own page: DS1307tiny

 

Working with DS1307 Real-time Clock and ATtiny85 using USITWIX Library

Working with the DS1307 Serial Real-Time Clock using the USITWIX library for I2C / TWI on Atmel ATtiny85 / Tinusaur.

Let’s see how can we work with the DS1307 serial real-time clock using the USITWIX library for I2C / TWI on Atmel ATtiny85 / Tinusaur.

Bellow is the testing setup.

NOTE: We need the USB-to-Serial just for debugging – it isn’t essential part of the setup.

There is no library yet to do that but with in the testing code there are few functions that could do the job.

Here is brief a description of the functions:

• uint8_t ds1307_read_reg8(uint8_t reg_addr) – reads one byte of data from the specified register.
• uint8_t ds1307_write_reg8(uint8_t reg_addr, uint8_t reg_data) – write one byte of data to the specified register.
• uint8_t ds1307_init(void) – initializes the circuit by writing specific data into the registers.
• uint8_t ds1307_setdatetime(uint16_t year, uint8_t month, uint8_t date, uint8_t weekday, uint8_t hour, uint8_t min, uint8_t sec) – sets date and time.
• uint8_t ds1307_adjust(void) – this is helper function – it sets the date & time to a specific value – let’s not forget that a brand new circuit does not have correct date and time set.

There are 2 additional functions that are used to convert data byte to and from BCD format.

• static uint8_t bcd2bin (uint8_t val)
• static uint8_t bin2bcd (uint8_t val)

This is direct link to the source code of the testing program:
https://bitbucket.org/tinusaur/ds1307tiny/src/default/ds1307tiny_test1/main.c

Source code available at: https://bitbucket.org/tinusaur/ds1307tiny

More information about the library will be available at its own page: DS1307tiny

Working with BMP180 Pressure Sensor and ATtiny85 using USITWIX Library

In our previous post “USITWIX – Using UART as TWI / I2C” we looked at the USITWIX library that implements TWI / I2C communication between а  ATtiny85 micro-controller and peripherals. Let’s see now how we can use that library to work with the BOSCH BMP180 atmospheric pressure sensor and a ATtiny85/Tinusaur boards.

The BMP180tiny Library

So, we wrote a simple library (called it BMP180tiny) that uses USITWIX to read and write from/to BMP180 registers, retrieve the measurements, do some additional calculations and produce result suitable for use in an application.

Setup

Here’s the setup:

NOTE: We need the USB-to-Serial just for debugging – it isn’t essential part of the setup.

Here is a short fragment of initialization code

uint8_t bmp180_result;
if ((bmp180_result = bmp180_init()) != BMP180_RESULT_SUCCESS)
{
  return -1;
}

And here is now to use the functions …

// Read raw temperature
uint16_t temp_rawdata = bmp180_read_temp_raw();

uint16_t temp_10x = bmp180_read_temp10x();
// temp_10x holds the result dC, i.e. 123 means 12.3 Celsius

// Read raw pressure
int32_t pres_rawdata = bmp180_read_pres_raw();

// Read pressure
int32_t pres = bmp180_read_pres();
int16_t pres_hpa = pres / 100;
// pres_hpa holds the result in hPa (hectopascals)

// Read altitude
int32_t alt_x = bmp180_read_alt_x();
int16_t alt_dm = alt_x / 100;
// alt_dm holds the result in dm (decimeters)

The debugging output would look something like this …

t:raw=28622; t(dC)=253; p:raw/hi=5; p:raw/lo=4940; p(Pa)/hi=1; p(Pa)/lo=33948; p(hPa)=994; a/lo=24222; a(dm)=1552;
t:raw=28624; t(dC)=253; p:raw/hi=5; p:raw/lo=4964; p(Pa)/hi=1; p(Pa)/lo=33933; p(hPa)=994; a/lo=24307; a(dm)=1553;
t:raw=28623; t(dC)=253; p:raw/hi=5; p:raw/lo=4951; p(Pa)/hi=1; p(Pa)/lo=33939; p(hPa)=994; a/lo=22619; a(dm)=1536;
t:raw=28624; t(dC)=253; p:raw/hi=5; p:raw/lo=4942; p(Pa)/hi=1; p(Pa)/lo=33940; p(hPa)=994; a/lo=24560; a(dm)=1556;

NOTE: This is generated using OWOWOD library and hardware (not required by the library itself to work)

References

The source code is available at https://bitbucket.org/tinusaur/bmp180tiny.
— The library is in the “bmp180tiny” folder.
— A sample code could found in the “bmp180tiny_test1” folder.

The page about BMP180tiny and articles about BMP180tiny.

The page about USITWIX and articles about USITWIX.

New Library: USITWIX – Using USI as TWI / I2C

As we know, there’s no I²C on ATtiny85, not even the TWI (Two Wire Interface, which is basically I2C with a different name) that some other Atmel chips have, so I had to write my own that takes advantage on the built-in USI unit. This library is called USITWIX and will be presented in this blog post.

Of course, I used other people’s work write mine and they’re references in the source code.

The primary source is the Atmel application note AVR312: Using the USI module as a I2C slave that explains how to use the  built-in USI unit as I2C slave.

The source code is already available at https://bitbucket.org/tinusaur/usitwix.

Some important code fragments

Although the TWI and I2C is a synchronous communication protocol it still requires precise timing.

In the code there are few places where some fixed time intervals are specified and this is in the usitwim.h file:

#define T2_TWI 5 // >4,7us
#define T4_TWI 4 // >4,0us

These may need to be adjusted if the CPU runs at a frequency different than default 1 MHz.

Using the USITWIX library

The BMP180TINY is another library for working with the BOSCH BMP180 atmospheric pressure sensor.The source code is available at https://bitbucket.org/tinusaur/bmp180tiny along with some samples.

There is also a Variometer project that uses those libraries to produce audible measurements of the changes in the altitude by measuring the atmospheric pressure and taking into account the temperature. Such tools, or instruments, are often used by paragliders.

Video here:
https://www.youtube.com/watch?v=6JTnYuJGo4w

References

Here are some references to sources that I used while working on this project.

AVR312: Using the USI module as a I2C slave
http://www.atmel.com/Images/doc2560.pdf
C-code driver for TWI slave, with transmit and receive buffers; Compatible with I2C protocol; Interrupt driven, detection and transmission/reception; Wake up from all sleep mode, including Power Down.

TINY USI Interface in I2C mode and the AVR312 Appnote
http://www.aca-vogel.de/TINYUSII2C_AVR312/APN_TINYUSI_I2C.html
What’s wrong with the AVR Appnote?

ATTiny USI I2C Introduction – A powerful, fast, and convenient communication interface for your ATTiny projects!
http://www.instructables.com/id/ATTiny-USI-I2C-The-detailed-in-depth-and-infor/
I2C, it’s a standard that’s been around for around 20 years and has found uses in nearly every corner of the electronics universe. It’s an incredibly useful technology for us microcontroller hobbyists but can seem daunting for new users. This tutorial will solve that problem, first by reviewing what I2C is and how it works, then by going in-depth on how to implement I2C in Atmel’s ATTiny USI (Universal Serial Interface) hardware.

I2C Bus for ATtiny and ATmega
http://www.instructables.com/id/I2C_Bus_for_ATtiny_and_ATmega/
This two wire interface is formally known as the Inter-Integrated Circuit bus, or just the I2C bus and was invented by NXP when it was still Philips Semiconductors. If you’re reading this Instructable then you’ve probably heard of the I2C bus and may even have used it on a PIC or other microcontroller. While conceptually very simple, and supported by hardware resources on the AVRs, software drivers are still necessary to use the I2C bus. Atmel provides Application Notes (see the Resources later in this Instructable), but these are incomplete and don’t show any examples beyond communicating with another AVR device.

ATtiny85 and ESP8266 – do you really need that?

Yes, why not. And here is what I did …

(this will be series of posts about what I did with ATtiny85/Tinusaur and ESP8266 WiFi module)

First, what could be accomplished with such limited device as ATtiny85? It has 8 pins, 2 of which are for the power (Vcc and GND), one for the RESET (pin 1 – PB5), another one potentially for the OWOWOD debugging (pin 2 – PB3) through serial line, so there are 4 pins left: PB0, PB1, PB2, PB4.

ESP8266 module uses UART to communicate so it would require at least 2 pins to work – URxD and UTxD.

There is also CH_PD pin that controls the chip and could power it down.

At first it may look that this takes another 3 pins out but not really.

If we use the CH_PD to disconnect the ESP8266 module we can use the same pins for other purposes like connecting additional I²C devices to the micro-controller. This is what I did.

What are the challenges?

1) There’s no UART on ATtiny85 so I had to write my own that takes advantage on the built-in USI unit. The library is called USIUARTX and will be presented in another blog post. The source code will be uploaded at https://bitbucket.org/tinusaur/ very soon.

2) There’s no I2C on ATtiny85, not even the TWI (Two Wire Interface, basically I2C) that some other Atmel chis have, so I had to write my own that takes advantage on the built-in USI unit. The library is called USITWIX and will be presented in another blog post. The source code is already available at https://bitbucket.org/tinusaur/usitwix. The BMP180TINY library (Source code at https://bitbucket.org/tinusaur/bmp180tiny) uses it to communicate with an BMP180 pressure sensor.

That’s it for now.

My next post will be about the above mentioned libraries.