Development board for 8 pin AVR microcontrollers

I got a bunch of ATtiny13 AVR microcontroller chips because I tought it would be fun to see what you can do with a tiny 8 pin microcontroller. The thought first popped into my mind when I looked at a project for creating motor controller for an electric spinning wheel.

The project used the same chip as in an arduino with an arduino bootloader. The ATmega328 is a lot more expensive than a ATtiny13. You can get a tiny for around 20 Kr at e.g. electrokit in sweden.

Lots of projects such as motor controllers with buttons or a dial for controlling speed does not need anything more than a tiny13, and a small program. My first problem however hooking up the circuit below to program one of my tiny13s, is that it is easy to connect the cables to the programmer wrong.

The example above is not too bad because I used colored wires with one female and one male end. Thus I could connect the female end directly to the output of the programmer and the male end into the breadboard. But if you have to connect into the connector of a ISP6 cable then it is easy to get the pin numbering wrong.

So that is why I build the above curcuit first on a breadboard, tested it and then built it on the prototype board below.

It has a ISP6 connector (black 2x3 pins). With this there is only one way to connect the cable from your programmer, so it is very quick to connect your 8 pin AVR microcontroller to a programmer. A lot of devboards contains the bare minimum of components. I wanted to be able to test most of my ideas and programs directly on my development board without having the move the chip to another circuit to do actual work.

So my development board has the following inputs and outputs which I believe I will typically be using for most projects:

• 2 outputs connected to a green and yellow LED. These are connect to pins which can do PWM, since I will need that for motor controller programs.
• 2 digital inputs connected to push buttons. Assume pullup resistor is enabled.
• 1 analog input connected to a potentiometer.

If figured I would to projects with blinking LEDs, dimmers or motor controllers. All that will require PWM. Hence pin 6 and 5 were selected for output.

In the design it is worth nothing that the outputs of the AVR chip do not power the green and yellow LED directly. The reason for that is that pin 6 and 5 are used for in system programming, and are thus connected to our programmer.

Connecting LEDs directly to these same pins as used by the programmer could interfere with its operation. ATMELs datasheets(page 6) says you should put in a series resistor between the load and the AVR. 10K would be a good value. I put in 22K and a transistor so very little current or voltage drop will happen to drive the LEDs.

I can program the AVR without any external power because the AVR-ISP500 programmer I use delivers power to the AVR through pin 2 of ISP6 connector. With the transistors I am also able to program it while external power is connected and the circuit is running. This makes development a lot faster, because I do not need to unplug anything to test the circuit, or plug in anythin to transfer an updated version of my program.

Here is a very simple program I ran on it to make one of the LEDs blink. I will not explain the program here, because it is just something for you to try, to make sure it works.

  .include "tn13def.inc"
  .def a = r16
  .org 0000
   rjmp Reset

Reset:
   ;define output
   sbi DDRB, PB0
   sbi DDRB, PB1
   cbi PORTB, PB0 ;turn off LED
   cbi PORTB, PB1

   ;set prescaler to divide clock freq by 1024. 
   ;each count is about 0.8ms at 1.2MHz
   ldi a, 1<<CS02 | 1<<CS00
   out TCCR0B, a

   ;set blink frequency
   ldi a, 250
   out OCR0A, a
   ldi a, 250
   out OCR0B, a

   ;set CTC mode (clear timer/counter on compare)
   ldi a, 1<<WGM01 | 1<<COM0B0 | 1<<COM0A0 
   out TCCR0A, a 
loop:
   nop
   rjmp loop