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Atmega 16/32 module v. 1.2
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On this page a small board for Atmel AVR ATmega16(L) and ATmega32(L) (TQFP44 package) is introduced. On the board, a crystal, a RESET pushbutton, an ISP connector for microcontroller programming and other components are provided. All microcontroller signals may be accessed through connectors provided on the board outline. In order to program the microcontroller an external programmer is required, as an example the Atmel STK500 development system.

Main characteristics

The small development board here introduced has been designed mainly to develop applications with Atmel AVR ATmega16(L) e ATmega32(L) microcontrollers in the TQFP44 package, while being available only the traditional Atmel STK500 development bord, which can not carry microcontrollers in a TQFP44 package.
The board here introduced does not have on-board peripherals or other devices, like EEPROMs, etc., therefore it is not an evaluation board; its simplicity makes it instead available to interface the mentioned microcontrollers with several kinds of application circuits. If the STK500 is available, it is possible to use some of its features, as an instance the PC-controlled supply, the level converter between microcontroller logic levels and RS-232 levels, etc..
In figure 1 it is shown the ATmega16/32 module interfaced with external circuits through Amphenol pin terminated wires and with the STK500 through an ISP programming flat cable. On the board shown in figure 1, single row, 2.54 mm pitch, 90° connectors are mounted. Using single row, 2.54 mm pitch, straight connectors, the board could also be mounted on other PCBs or prototype boards with proper sockets.

Figure 1 - The ATmega16/32 module v. 1.2 connected to the STK500 through an ISP cable and to other devices

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Acknowledgement and disclaimers

The design and realization of the board here introduced have been carried on by the undersigned in first person, though on the net something analogous may be surely found.

Should the content of this page be used for not merely personal or educational purposes, or should it be made available to others, included in Web pages and so on, it is compulsory to ask a written permit (by mail) to the author of this article. The use of this board for personal or educational usage is absolutely free.

The informations on this page are published without any warranty. The author of this article does not assume, of course, any responsibilty for possible direct or indirect damages to things or persons deriving by the use of the informations contained in this article. 

Notes concerning the use of the module

As it can be seen in the electrical schematic in figure 2, the circuit is quite simple.
The clock source is a crystal: it may be useful to use a crystal holder or a 5.08 mm pitch connector, in order to make it possibile to use different crystals.
Before applying supply, it is warmly advisable to read carefully the datasheet of the mounted microcontroller and to look at the electrical schematic of the module, concerning in particular the supply allowable range and the possible need to connect each other through on-board connectors some supply pins of the module, GND and/or VCC.
The module has been realized and tested with ATMEGA32L and ATMEGA16 microcontrollers; with both devices, 16 MHz and 8 MHz crystals have been tested.
Before connecting the board to the programmer, it is warmly advisable to look at the electrical schematic of the module and to read carefully the programmer datasheet, concerning in particular supply and RESET circuits.
Concerning the supply, it is possible to feed supply to the ATmega16/32 module through the ISP connector if the programmer allows it, obviously taking care not to exceed the programmer current limit; it is possibile to supply the board with an external supply, but in this case it is necessary to take care to avoid problems with the programmer ISP pins if the ISP cable is connected to the programmer.
Concerning the RESET signal, in order not to damage the programmer RESET circuit in case the RESET pushbutton is pressed while the RESET signal is driven by the programmer, a resistor has been provided between the on-board RESET pushbutton and the RESET ISP pin; the resistance value i suitable for the use with the STK500, but it may not be suitable with other programmers.

Figure 2 - Electrical schematic

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PCB realization

The module may be realized on a FR4 double sided board. In figures 3 and 4 the top and bottom layouts are shown.
The high resolution images can be downloaded through the images caption links. Note: images on this page could be low resolution images. The images downloadable through caption links are 600 dpi images. In order to verify that the printed image is a true size image, you may check that the distance between the extreme pins of the 11 pin connectors is 25.4 mm. It is advisable to check both horizontal and vertical connectors.
The mimimum track width is 0.4 mm. With a good quality master, as an example a master printed on a film, the board may be realized with a home made photoetching process. It may be possible, but it has not been tested, that good results could be obtained with masters printed by a LASER printer, possibily using 2/3 overlapped masters.
With a home-made process, it is necessary to use wires or component terminals for vias, and to solder on both sides the component terminals used to connect the top and bottom sides, as an example the terminals of some capacitors.
It may turn out not easy to solder some connector pins; in case of connectors joined by a plastic shell, an attempt may be made moving the plastic shell.
Soldering the microcontroller is not a trivial task, but with a bit of experience in SMD soldering it generally turns out successfull. It is not adviceable to solder the microcontroller without any SMT soldering experience. Before applying power to the circuit it is recommended to clean the board from flux residuals and to check track continuity.

Figure 2 - Top side layoutFigure 3 - Bottom side layout

Figure 4 - Top side silkscreen

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Component list

Components needed are listed below. Component values are not critical.
Capacitors should stand at least 50 V.
Resistors be at least 125 mW.
      Ref.   Kind/Value    Package   
1    C1    KER 22 pF    8X3R5,08   
2    C2    KER 22 pF    8X3R5,08   
3    C3    100 nF    8X3R5,08   
4    C4    100 nF    8X3R5,08   
5    C5    100 nF    8X3R5,08   
6    C6    100 nF    8X3R5,08   
7    C7    10 nF    8X3R5,08   
8    CMP1  Double side board, 58 mm x 42 mm   
9    IC1    ATMEGA32L-8AI    TQFP44    ( Note 1 )
10    K1    K1X11    1X11    -  SIL connector, 2.54 mm pitch
11    K2    K1X11    1X11    -  SIL connector, 2.54 mm pitch
12    K3    K1X11    1X11    -  SIL connector, 2.54 mm pitch
13    K4    K1X11    1X11    -  SIL connector, 2.54 mm pitch
14    K5    K2X3    2X03    -  DIL connector, 2.54 mm pitch (for ISP programming)
15    L1    L-air 10 uH    R5      ( Note 2 )
16    Q1    QUARZ_8,0000MHZ    HC49/U    ( Note 3 )
17    R1    4.7 KOhm   R5   
18    R2    470 Ohm   R1   
19    S1    SMD pushbutton N/O   TACT_DTS-644   

Note 1: Suitable ICs: ATMEGA16, ATMEGA16L, ATMEGA32, ATMEGA32L, package TQFP44
Note 2: The inductor L1 is not strictly needed if the ATmega 16/32 internal ADC is not used, and may be replaced with a bridge, in order to connect the ATmega 16/32 AVCC pin to VCC.
Note 3:  Tested crystals: 8 MHz, 16 MHz with ATMEGA16 and ATMEGA32L

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Final notes

I have personally used the module here introduced for a few applications, above all during the pre-prototype phase of circuit development. As an example, I have used it for ADC conversion, for I/O pins control through commands from a PC via RS-232 (using the STK500 on-board level converter), for I2C communication with other devices, etc..
Before successfully using the module for some applications, preliminar or experimental investigations should be carried on. Just as an example, in case AD conversion must be used, care should be taken concerning the 50/60 Hz noise if connecting the module to other circuits with long wires.
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