LCD-LED Display

Mini Experimental Board for ATtiny45 Schematic Circuit Diagram

This very simple little development board was designed for carrying out tests on the 8-pin AVR microcontrollers from Atmel. Any 8-pin IC with power on pins 8 (+5 V) and 4 (0 V) can be used, checking of course that the programming pins are the same as on the ATtiny45 for which this board was made.

Mini Experimental Board for ATtiny45 Schematic Circuit Diagram

The IC’s eight pins are brought out onto two rows of PCB pins and two screw terminal blocks (K1 and K2) with a 0.2” (5.08 mm) pitch. There are three possible ways to power the board: from an external 8–12 V (15 V) PSU via a standard power socket; from a 5 V rail via the programmer’s ISP connection (if the jumper is fitted); or by three 1.5 V cells via a switch. If batteries are not being used, a prototyping area with solder pads is available. There’s an LED to indicate the presence of power.

For experimenting, there are three tools on the board. First of all, a simple logic probe with an LED and its current-limiting resistor, then a potentiometer adjustable between Vcc and ground, which gives us a variable voltage for the A/D converters, and lastly a pushbutton which makes to the ground when pushed. Although SPI access connector K4 is shown as 6-pin in the circuit diagram, a 10-pin HE10 connector is actually used on the circuit board.

Two 18 pF SMD capacitors are provided for a crystal oscillator. These don’t interfere with operation even if a crystal is not used. Their rather unorthodox connection (one to the ground, the other to +5 V) has made it possible to simplify the PCB layout slightly. The 1N4007 diodes can be either conventional or SMD types, as can the resistors and certain of the decoupling capacitors. Printing the component layout onto glossy photo paper using an ink jet printer gives a very clean finish that is also extremely robust (even against alcohol). The PCB design, component overlay, and a few photos are available on [1].

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