AVR ATMEGA 8535/16/32 (40 Pin IC) System Board

Here is system board for AVR ATMEGA 40 pin IC which i’ve designed.

Feature:

– I/O pin with VCC GND in each port

– Socket IDC for LCD alphanumeric 16×2

– connector DB9 for USART serial communication

– regulated power input (range 6-12 V)

– External Crystal Oscillator 16 MHz

– Port For ADC reference voltage, jumper only for 5V reference

– ISP downloader port

There are some main part in creating system board for AVR microcontroller:

– reset circuit

– power supply

– oscillator

Reset Circuit:

This part contain a pull-up resistor, capacitor and push button.

Pull-up resistor is used to keep the voltage in reset pin in 5V. This is required for reset pin is active low, thus the resistor will keep the IC from always resetting.It is connected between VCC to reset pin. The value is usually 5-10k.

Capacitor is needed for making a slow start on reset pin. While power is on, voltage in reset pin will rise slowly and give time for oscillator to be in steay state. If capacitor is not added, there are some case that require manual resetting by user. it is connected between reset pin and ground.

Push button is used for manual resetting by user, in case there some error in running program. There are other ways to handle error, but i will not write about them in this. Push button is connected between reset pin and ground. When push button is pressed, voltage in reset pin will be forced to 0V and trigger the reset interrupt

Push Button is used for manual reset.

Power Supply:

This is part which supplies the voltage needed for IC operation. AVR usually requires 4,5 – 5,5 V but for some other type, the voltage maybe lower. I use 7805 voltage regulator. It is really cheap way to provide 5 volt for IC  which cost only about Rp 2000. Input voltage range is 6-12 V. I add some capacitor in the input and output to prevent ripple from supply or load. Bigger value is better for bypassing ripple and acting as temporary additional supply when load draws too many current. Current output is 1 A in datasheet.

Oscillator Circuit:

Oscillator circuit acts as clock source for operating IC. There are some option for clock source, but i will give the external crystal oscillator circuit. It is good and commonly used because it has precise and bigger value than other type. in AVR 40 pin which i mentioned above, the maximal value is 16 MHz. This circuit contains oscillator crystal and two capacitor. Crystal is connected between pin Xtal1 adn Xtal 2 in AVR IC. Capacitor is connected between each crystal and ground.

With the three parts, your AVR are ready to be used. The other part are added as you need.

I have used this board for testing of  some of my microcontroller AVR related projects. it can communicate to hyper terminal in windows from DB9 connector via USB to serial RS 232, display character in LCD and interfacing to other hardware like led, transistor and other microcontroller.

I hope this is useful for you. If you have any question, i will try answering it.

Adi Wiguna