010076-I

Projects/Microcontrollers

Elektor AVR

programmer

Simple universal AVR programmer

with USB interface

Dipl.-Inf. (FH) Benedikt Sauter and

Dr. Thomas Scherer

This companion to

the Elektor AVR

project is a plug-and-

play AVRISP MkII-

compatible USB

programmer for AVR

microcontrollers.

Elektor asked Benedikt Sauter to
design a simple AVRISP MkII-
compatible programmer which can be
used with a wide range of software. It
is particularly suitable for use with the
ATM18 test board used in our
microcontroller programming course.
The main requirement was that the
programmer should be as simple in
design and use as possible and as
inexpensive as possible. The result
was the simple dedicated USB
programmer described here.
In comparison to the earlier USBprog
design the circuit has changed little
(Figure 1), the main update being that
an ATmega32 is used in place of the
ATmega16. The printed circuit board
(Figure 2) has been made smaller,
thanks to the use of a miniature USB
socket and a 6-way header rather than
a 10-way header for the ISP interface.
The May 2008 issue of Elektor will
include a more detailed discussion of
this.

O F T W A R E

Being a clone of the AVRISP MkII
programmer, the Elektor design is
compatible with a wide range of
software. Since we are using Atmel’s
AVR Studio 4 [3] with the test board,
we can use it to install the relevant
driver (see Figure 3). After the driver
has been installed we can connect the

Figure 1: The circuit diagram of the Elektor USB programmer is broadly similar to its
predecessor described in the October 2007 issue of Elektor. A USB bridge and a microcon-
troller are the main components.

module to the PC and Windows should
then automatically recognise the new
hardware and select the correct driver.
In some Windows XP installations,
however, an error message is
produced, claiming that the file
‘libusb0.sys’ is not found. Ignore this
error message and click ‘Cancel’. The
driver will nevertheless be found and
installed and all will be well.

It is now possible to use the
programmer with a wide range of
software, including CodeVision AVR
[4]. Unfortunately, the programmer
cannot be used directly with Bascom
[5] as that software does not yet
implement the AVRISP MkII
protocols.
For non-Windows users there is a
greater choice: do an internet search
for ‘Linux’, ‘AVRISP MkII’ and
‘software’. For Linux and Mac OS X
the open source ‘AVRDUDE’
software [6] is particularly
recommended. Since this software is
driven from the command line, we
have also made available a file

‘Elektor-AVRprog Mac.pdf’ which
explains how to integrate AVRDUDE
with a ‘proper’ user interface.

O I N T S T O N O T E

The ‘bitrate’ to which the programmer
is set should not be greater than one
quarter of the clock frequency of the
microcontroller being used. The
programmer supports bit rates from

249 Hz to 2 MHz. From version 4.13,
AVR Studio refuses to run the
programmer at frequencies of less than
5 kHz. Figure 4 shows how the ISP
frequency is set in AVR Studio.
If any problems arise it is worth
checking [2] to see if a new version of
the firmware is available. To
reprogram the firmware it is necessary
to bridge the two holes next to the
quartz crystal on the programmer.
Then the new firmware can be loaded
over the six-pin ISP connector using a
second programmer.
It is worth remembering that the
programmer uses 5 V logic levels. If
the target device is supplied with 3.3 V
(or even less) during programming,

this can cause problems. The solution
is to operate the target device from 5 V
during programming.

ATM18

T E S T B O A R D

Pin 1 of the 6-pin ISP connector K13
is located nearest to the
microcontroller module (Figure 5).
During programming JP1 should be set
to the ‘EXT’ position if the board is
powered from a mains adaptor.
Alternatively, set JP1 to ‘USB’ and the
board will draw power from the USB
port via K5.

B O U T T H E A U T H O R

Benedikt Sauter is a passionate open
source hardware and software
developer and for this project is
responsible for the building and
maintenance of open source
applications.

Figure 2. The assembled module. Thanks to the use of a mini USB connector and a 6-
pin ISP connector the unit can be very compact.

Figure 5. Pin 1 of the 6-pin ISP interface is
the one nearest to the microcontroller mod-
ule.

I N K S A N D R E F E R E N C E S

[1] ‘USBprog’, Elektor, October 2007

[2] Project

website:

http://www.embedded-
projects.net/usbprog

[3]

AVR Studio 4:

http://www.atmel.com/avrstudio

[4] CodeVision

AVR:

http://www.codevision.be

[5] Bascom: http://www.mcselec.com

[6] AVRDUDE:
http://www.nongnu.org/avrdude

O U R C E S

The USB programmer is available
from Elektor as a ready-made SMD-
populated printed circuit board
including USB and ISP cables for 32
Euro.

You can order via
http://www.elektor.com or via the
Elektor shop.

Figure 3. Screenshot from the installation of AVR Studio 4. As soon as the software and
drivers are installed the programmer is ready for use.

Projects/Microcontrollers

Parallel

programmer

Ultra-simple STK200- and STK300-

compatible AVR programmer

Dr. Thomas Scherer

For some, even the

low-cost USB

programmer for the

ATM18 test board

described in the

accompanying series

of articles might

seem a little

expensive. Here is

an even cheaper

solution, using just a

couple of resistors!

Elsewhere we describe a simple and
inexpensive USB programmer for
AVR microcontrollers, designed for
use in conjunction with the
microcontroller programming course
and ATmega88 module and test board.
However, if the full flexibility of that
programmer is not required, it is
possible to simplify the design and
reduce its cost even further.

H E C H E A P E S T

P O S S I B L E P R O G R A M M E R

It may come as a surprise to learn that
the ISP (in-system programming)
interface of an AVR microcontroller
can be driven directly from a parallel
port, and indeed this is how Atmel’s
early STK200 and STK300
programmers worked. All that is
needed to make a fully-functional
programmer for AVR microcontrollers
is a PC with a parallel printer port.
Four resistors are needed to protect the
port and the target device from one
another. The de luxe model of the
programmer sports an extra resistor
and a low-current LED to show when
data transfer takes place between

programmer and target device.

H E C I R C U I T

Calling Figure 1 a ‘circuit’ is perhaps
stretching the term. Besides the ground
connection and the wiring of pins 2
and 3 of the printer port back to the
flow control signals, just four 270 Ω
resistors, R1 to R4, are needed. Pin 7
can be used to drive a low-current
LED via a 1 kΩ resistor to give a
visual confirmation of data transfer,
but this is an optional extra.

O N S T R U C T I O N

The minimalist circuit can easily be
built on a small piece of perforated
prototyping board. The output takes
the form of 6-pin header K2, the ISP
connector. On the input side you can
either use a Centronics socket in
conjunction with an ordinary printer
cable, or a 25-way sub-D insulation
displacement connector (IDC) to fit
the port on the PC, a suitable length of
ribbon cable, and a two-row 26-way
IDC header, with a corresponding
socket on the programmer board as
shown in Figure 2. The result is a neat
and practical parallel programmer.

O F T W A R E

Since the programmer is compatible
with the STK200 and STK300
devices, it will work with a wide range
of existing software. Indeed, when
configuring programming software
either ‘STK200’ or ‘STK300’ should
be selected as the programmer type.
The programmer works perfectly with
both CodeVision [1] and Bascom [2]
software and the ATM18 test board
(Figure 3). Sadly, Atmel’s own AVR
Studio 4 no longer supports parallel
programmers, but the alternatives
make more than adequate substitutes.

ATM18

T E S T B O A R D

Pin 1 of ISP connector K13 on the
ATM18 test board is the one nearest to
the microcontroller module, as shown

in Figure 4. If the connector is
inserted the wrong way round no harm
will be done, but the device will fail to
program.

Also note that JP1 on the test board
should be set to ‘EXT’ during
programming if the test board is
powered from a mains adaptor capable
of providing 7 V to 16 V at a current
of a few milliamps. Alternatively, set
JP1 to ‘USB’ and the test board will be
powered from the USB interface via
K5.

O T A B E N E

If the parallel programmer is used in
other projects, it is worth remembering
that the printer port works with 5 V
logic levels. If the target device is
powered from 3.3 V or less during
programming, it may not function
correctly. In such cases power the
target microcontroller from 5 V, if
necessary transplanting it to a
prototype board for programming.
Some laptops have a parallel port that
operates using 3.3 V logic levels. This
will sometimes result in failure to
program a microcontroller running on
a 5 V supply.

I N K S A N D R E F E R E N C E S

[1] CodeVision

AVR:

http://www.codevision.be

[2] Bascom:

http://www.mcselec.com

Reaction timer

Bonus program example for the
Elektor AVR project

Fancy a game? Here is a little test of skill in the form of a reaction timer. The only hardware required is a pushbutton,
which is already available on the ATM18 test board. The button is connected to port PB0 of the ATM18 module, which
is an input with an internal pull-up resistor. In fact we do not need the pull-up resistor in this experiment as all the
pushbuttons on the board are already equipped with pull-up resistors, but it does mean that the example will still work if
the microcontroller board is used in stand-alone configuration. The game could be built into a tiny enclosure with a 3 V
lithium cell as power source.

A S C O M L I S T I N G F O R T H E R E A C T I O N T I M E R

I M E

B A S

)

'Time of reaction measured on PB0, output on 6 LEDs on PortC

$regfile = "m88def.dat"

$crystal = 16000000

Config Portc = Output

Config Portb = Input

Portb = 255 'Pullups

Config Portd = Input

Portd = 255 'Pullups

Dim Leds As Byte

Dim Timeout As Word

Leds = 1

Portc = 255

Timeout = Rnd(1000)

Timeout = Timeout + 500

Waitms Timeout

Portc = 0

Timeout = 0

Timeout = Timeout + 1

Waitms 10

Loop Until Pinb.0 = 0 Or Timeout = 127

Leds = Timeout

Portc = Leds

Waitms 1000

Loop

The outermost infinite do loop means that the program repeatedly carries out new reaction time measurements. First all
the LEDs are turned on and then there is a random delay of between 0.5 s and 1.5 s. The randomness ensures that the
player cannot get used to the rhythm of the game. Tension builds, and suddenly all the LEDs are extinguished! The
player must now press the button as quickly as possible, and the reaction time is counted in units of 10 ms. The result is
displayed in binary on the LEDs, which gives the player the bonus mental exercise of converting the result to decimal.
For example, the display 0010011 means that the measured time was 19 times 10 ms, or 190 ms (which is a pretty
impressive performance). With a bit of practice your grey cells will get used to doing this conversion in the one second
the game allows before the next trial begins!

P R O J E C T

On the Elektor website you will find not only the two Bascom projects but also the C project ATM18_Demo1 by Udo
Jürß, created using the IAR compiler. The project is also a reaction timer game, but this version also uses the serial
interface. The functions and required connections are listed in the program source code. Port C is used to drive six
LEDs, and PD2 is used to drive the seventh LED. PD0 and PD1 are used for the serial port, and two buttons are needed,
connected to inputs PB0 and PD6.

More advanced experimenters will find in this example many elements and techniques that they can adapt for more
complex projects, including the use of timers, interrupts and advanced output operations using the serial port. The
program also demonstrates how to respond to commands received over the serial port. For example, it would be
possible to arrange to turn individual outputs on and off or carry out various types of processing in response to serial
commands.

T H E R

C O M P I L E R S

We have also modified the first C project for the Elektor AVR board by Benedikt Sauter so that the source code can be
compiled using WinAVR GCC, and Antoine Authier has contributed a suitable Makefile. It is also planned to make a
version of this project available that is suitable for use the the CodeVision AVR C compiler. Future C projects in this
series will be made available for the CodeVision compiler as well as for WinAVR GCC.

O N T E N T S O F T H E F I R S T S O F T W A R E D O W N L O A D

Elektor AVR download part 1 (071148-11.zip):

- [ATM18_Demo1.zip] with C source code for the IAR compiler by Udo Jürß

- [Bascom.zip] source code in Bascom AVR Basic

- [ATM18_Hello_GCC.zip] modified C source code by Benedikt Sauter for use with WinAVR GCC

- [makefile_for_hello_on_ATM18.zip] Makefile for AVR GCC (using WinAVR or under Linux or other operating
systems) by Antoine Authier

Document Outline