ETT boards : MRT 8535 SDK

This is not an ETT board. This board is made by Micro Research Technology and it is known as the 'AVR-SDK2+'. And it's a nice board. Take a look at the picture and you see:

AC/DC power jacks with full bridge rectifier and voltage regulator (with a big heatsink)
Lots of connectors for taking off signal pins
ISP connector (proprietary format)
Big breadboard area, glued to the PCB
Development support:
- 4 pushbuttons
- 4 trimpots between +5V and Ground
- 8 LED's
- Buzzer
- Character LCD port
I2C bus interface:
- Socket for DS 1307 with crystal and battery connector pre-installed
- Socket for I2C EEPROM
- Socket for I2C signals SDA and SCL
Fully built RS 232 interface based on MAX 232, with the matching DB9 cable
Reset button
Mounted on a heavy duty plastic base with mounting holes

Now, that's what I would call value for money. The only nuisance is the yet once more non-standard pinning of the ISP cable connector. Apparently MRT would prefer me to buy their own programmer as well. Fortunately for me, Futurlec do not sell this item. But with a few lengths of wire and a few 10 pin boxed connectors, we can make our own pinswapper cable.

The AVR-SDK2+ series microcontroller development board is designed on the basis of easy to use and low cost. The board is available for the 20 pin ATtiny2313 and the 40 pin ATmega16/32/8535. The program can be uloaded to the processorboard using In System programming (ISP). The MRT programmer board is a seperate unit so that you can use it for your other MRT boards as well. For the rest, this board is populated with the things you require when experimenting with a (new) microprocessor.

Specification for the AVR8535 model

8 MHz Crystal
8 status LED's
4 pushbuttons
Piezzo speaker
4 trimpots for setting voltages (between 0 and 5 Volts)
Ports A to D brought out on seperate (grouped) 10 pin IDC connectors
LCD port in 4 bit mode
RS232C port
MCU upload port (MRT-ISP loader)
RTC crystal 32 kHz (for the optional DS1307)
Optional I2C EEPROM
Big breadboard area

This development board was designed to be used with two kinds of power connectors:

2.5 mm barrel connector (DC jack)
2 pin terminal block

Since there is a full wave bridge rectifier behind the connectors, the polarity of the 'DC jack' is irrelevant. Behind the rectifier is a 470 uF/25V electrolytic capacitor, followed by a 7805 regulator, mounted on a large heatsink. On several places on teh board you can find pick up points for both power and ground.

To the right you see how the four trimpots are connected. The most obvious application for these is testing the Analog to Digital Convertors and internal analog comparators.

And to the left you see how the pins are available on a terminal block using all kinds of pins.

This is the LCD port, which is controlled by the B port. The interface is 4 bits wide only.

Jumper 16 selects the RD/WR pin of the LCD module between 'controllable' and 'Write Only' modes. The trimpot is used to vary the contrast of the LCD.

This 10 pin IDC header (boxed header) is used to bring out the 8 pins of Port A to the exterior. The scheme is self explanatory.

This 10 pin IDC header (boxed header) is used to bring out the 8 pins of Port B to the exterior. The scheme is self explanatory.

This 10 pin IDC header (boxed header) is used to bring out the 8 pins of Port C to the exterior. The scheme is self explanatory.

This 10 pin IDC header (boxed header) is used to bring out the 8 pins of Port D to the exterior. The scheme is self explanatory.

To the right, you see the way Micro Research Technology has made their own ISP pinout. I call this a pity. Why come up with yet another pinout? To protect the own interests? Could be so, but people who already invested in a standard ISP programmer will now think twice (or more) before ordering this otherwise great board.

The circuit says it all. MRT use the older version of the MAX 232 but that's no problem since they also use big enough capacitors.

As you can see, only one RS232 channel is used.

The boards comes with the matching cable (3 pin to DB-9).

The board is equipped with 8 red LED's with current limiting resistors on the anode and the cathodes grounded. This way, a logic '1' on the input will light up the LED. The drive current seems to be around 10 mA. The circuit is simple, yet effective. If you lasted on this site for more than 5 minutes, this kind of circuit should not pose a trouble at all.

Jumperblock 1 is used for connecting the 4 pushbutton switches and the (buffered) piezzo buzzer. A logic '0' will pull open the BC557 PNP transistor.

You could use a pushbutton to test the speaker.... :o)

The board has the I2C signals brought out to a 4 pin headerblock.

To further complete this section, the boards has pre-installed two IC sockets for I2C peripherals: an EEPROM and a realtime clock (with battery support). The realtime clock must be a DS1307 (or compatible) and it is connected as shown to the right.

The manual is rather unclear about two resistors on the back of the board that need to be removed when a battery is connected. But there are no resistors on the back of the board...

The breadboard is here.

Page created on 5 February 2009 and

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