Savel brain dump in English!

There are lots of chips with serial control. Some of them use Philips I2C buss. There two data lines and two power lines to transmit all data. There DTMF encoders, switches, Dolby surround audio processors, multiplexers and many many other devices. Just open any TV set and you can find some- like TV tuner. ATMEL chip has build in serial interface, but it is called TWI. In my PCB there are two bigger SMD pads to connect I2C buss. Don’t forget to solder 10K pull up resistors.

For testing TWI bus I selected I2C temperature sensor. It is LM75 or any other clone. I am using small PCB from old plasma display panel with Fairchaild FM75 chip. It is smarter and more precise clone of original LM75. FM75 is backwards compatible with LM75. It has more precision and this means more data bytes available to read. At full precision it used 12 bits for temperature. In my software I used simplified algebra to convert 1/16 fractions to metric system. For more precise calculations, read FM75 and LM75 datasheet. And maybe AD7416 datasheet too.

I am using i2c.c from internet, from USB Tenki project. This project is very interesting, pay a visit to original Tenki web page for more advanced device. lm75.c is from same source. LCD modules are same as in older my web blog posts. When you connect your LM75 chip, don’t forget to check the device address- base address is the same, but user selected pins maybe connected in other way.

Programa: 20070919.zip.

With these chips and software example it is possible to build some thermostat project. But don’t write all controll stuff for ATMEL chip. Read the datasheet again and use LM75 thermostat option. Use ATMEGA only for control, display and setup.

There is ADC in ATMEGA16 with 8 multiplexed inputs. This analog to digital converter have several interesting options. Here is abstract from datasheet:

• 10-bit Resolution
• 0.5 LSB Integral Non-linearity
• ±2 LSB Absolute Accuracy
• 13 – 260 μs Conversion Time
• Up to 15 kSPS at Maximum Resolution
• 8 Multiplexed Single Ended Input Channels
• 7 Differential Input Channels
• 2 Differential Input Channels with Optional Gain of 10x and 200x(1)
• Optional Left adjustment for ADC Result Readout
• 0 – VCC ADC Input Voltage Range
• Selectable 2.56V ADC Reference Voltage
• Free Running or Single Conversion Mode
• ADC Start Conversion by Auto Triggering on Interrupt Sources
• Interrupt on ADC Conversion Complete
• Sleep Mode Noise Canceler

The ATmega16 features a 10-bit successive approximation ADC. The ADC is connected to an 8-channel Analog Multiplexer which allows 8 single-ended voltage inputs constructed from the pins of Port A. The single-ended voltage inputs refer to 0V (GND). The device also supports 16 differential voltage input combinations. Two of the differential inputs (ADC1, ADC0 and ADC3, ADC2) are equipped with a programmable gain stage, providing amplification steps of 0 dB (1x), 20 dB (10x), or 46 dB (200x) on the differential input voltage before the A/D conversion. Seven differential analog input channels share a common negative terminal (ADC1), while any other ADC input can be selected as the positive input terminal. If 1x or 10x gain is used, 8-bit resolution can be expected. If 200x gain is used, 7-bit resolution can be expected.
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is held at a constant level during conversion. The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ±0.3 V from VCC. Internal reference voltages of nominally 2.56V or AVCC are provided On-chip. The voltage reference may be externally decoupled at the AREF pin by a capacitor for better noise performance.

Software is very simple. It just read data from ADC and prints the results to LCD module. With small change in the source (just uncomment fre lines) and it is possible to read data from all channels.

Changing value near text “Stepas” just indicate the cycle number (in default program version) or ADC channel number. And if this number is changing, we can determine, that software is still working 🙂

Sorftware, source code: 20070918.zip.

Blinking LED is not very cool. And not very informative. But we can use LCD module. It is very cheap and available device. There are many types of LCD modules in the world. I am using most popular- HD44780 controller based alphanumerical module. It is 2 lines, 16 symbols. There are 14 or 16 pins on this module. Two extra pins are used for backlight. All other pins are used in 8 bit mode. As MCU pins can be used for more usefull purposes, we use 4 bit mode- every byte is transfered in two cycles. As MCU is very fast, we can not notice any lag here.
LCd module has selftest mode. When we connect power supply we must see upper line in black. If, not black square are here, try to adjust contrast using the only available trimmer on the PCB.

LCD control software is from internet. After several experiment I selected Peter Fleury program. Other versions I tested had some hardware limitations. LCD connection is described in lcd.h file. No need to change lcd.cfile. But you can peek to it to find what procedures are in here.

Testing program is in test_lcd.c file. There is some push button routines here too. I am using jumper named “firmware” as button.

If you power this device from computer’s USB slot, don’t pay attention to windows messages about unknown device connected to USB buss. We solve this problem later.

Software source and hex file for testing is here: 20070917.zip.

Now we need to test PCB and MCU. To test this hardware we need to run some program. And to build program we need tools. I downloaded and used free software from internet. WinAVR package: http://winavr.sourceforge.net/. Also, I am using programmers notepad2. It is useful tool for MCU programmer.

First program is simple LED flasher. We will test if MCU is working and if all LED diodes are working and all pins of MCU is properly soldered. The only LED will be on all the time is power LED. As the photo is made with long exposure, it seams, that all LEDs are on. In real, they are flashing in binary way.

(My printer is dead, so the PCB is ver ugly)

Software source and hex file: 20070916.zip

Software is very simple- we just set some pin to output and start counting cycle. Counting results are set to output pins. It is bad programming practice to put whole byte to several pins. In real world we need to alter only these bits we need to change- never put data to unused pins or input pins. But this program is for testing only.

Few comments. As I mentioned, mine LPT port is damaged, so I am using add on card. So, edit “makefile” for your programmer. You must check the “program”section. In my version there is few words to describe port address of my add on card:

program: $(PRG).hex
avreal32 -pBC00 -ab -e +$(AVREALMCU)
avreal32 -pBC00 +$(AVREALMCU) -ab -w -c $(PRG).hex -v

Just change -pBC00 to you port. Use “avreal32 -h” for more information. Or, if you use other programmer, replace these line according your programmer manual. Or, don’t use “make program” menu item in editor’s toolbar.

Also, some words for absolute beginners. Typically you can find information about simple things- everybody know how to do and they even don’t think, that somebody will not know how to do simple compile things. So, to compile software use “make all” menu item from programmers notepad or from CMD prompt. The computer will print lots of stuff on screen, but the main message is at the end:Process Exit Code: 0 and if you don’t see any ERROR.
Command “make clean” or Tools->[WinAVR] Make Clean, cleans all compiled files. So if you change something in the source, use make clean to be sure.

And the last menu item, make program or Tools->[WinAVR] Program we program firmware to MCU.

Few words about security bits. Carefully read original Atmel documentation. Sometimes these bits are mixed in various documents. Some tell that “set” means write 1, others- vice versa. It is possible to set MCU to “closed” mode and it will not be visible by programmer. As I am using “second hand” MCU I don’t need to change fuse bits. Mine bit looks like this:

Fuses
OSCCAL = AD, AB, A7, A8
BODLEVEL = 0
BODEN = 1
SUT = 2
CKSEL = F
BLB1 = 3
BLB0 = 3
OCDEN = 1
JTAGEN = 1
CKOPT = 1
EESAVE = 0
BOOTSZ = 3
BOOTRST = 1

As it is still working I am not changing any bit. Use this online tool http://palmavr.sourceforge.net/cgi-bin/fc.cgi

You can find HEX file in archive, so you can test hardware without any compilation.