Bill of Materials

The I/O expansion board should comprise 8 Digital Inputs, 8 Open-Collector Outputs, 2 Opto-Coupled Outputs and 2 power outputs. The complementary components consists of:

2 x Relays;
4 x Switches;
4 x LEDs;
2 x 7-Segment display;
1 x LCD display.

To implement I/O expansions it's also needed :

PC;
1 x Raspberry Pi 2;
1 x 40 GPIO connector;
2 x MCP23S17;
1 x ULN2803A;
2 x 4N25;
2 x 330 Ω Resistors; (opto)
2 x 10k Ω Resistors; (opto)
2 x Diodes 2N4007; (relay)
? x Jumpers;
PCB manufacturing environment.

4N25

ULN2803A

MCP23x17

The MCP12x17 device family provides a 16-bit general porpouse parallel I/O expansion for I2C or SPI applications. Specifically, the MCP12s17 is used for SPI serial interface.

Features:

16-Bit Remote Bidirectional I/O Port:
- I/O pins default to input;

High-Speed SPI Interface:
- 10 MHz (maximum);
Three Hardware Address Pins to Allow Up to Eight Devices On the Bus;
Configurable Interrupt Output Pins:
- Configurable as active-high, active-low or open drain;
INTA and INTB Can Be Configured to Operate Independently or Together;
Configurable Interrupt Source:
- Interrupt-on-change from configured register defaults or pin changes;
Polarity Inversion Register to Configure the Polarity of thr Input Port Data;
External Reset Input;
Low Standby Current:
- 1 µA (maximum);
Operating Voltage:
- 1.8 V to 5.5 V @ -40 ºC to +85 ºC;
- 2.7 V to 5.5 V @ -40 ºC to +85 ºC;
- 4.5 V to 5.5 V @ -40 ºC to +125 ºC.

The ULN2803A device contain eight NPN Darlington transistors with common emiters and internal supression diodes for inductive loads. Each Darlington features a peak load current rating of 600 mA (500 mA continuos) and can whistand at least 50V in the OFF state. It has a 2.7 kΩ resistor for 5 V TTL and CMOS. Outputs can be parallel for higher current capability. ULN20803A is going to be used to implement the 8 open-colector outputs.

Features:

500-mA-Rated Collector Current

(Single Output);

High-Voltage Outputs: 50V;
Output Clamp Diodes;
Inputs Compatible With Various

Types of Logic.

The 4N25 device consist of a gallium arsenide infrared emitting diode optically coupled to a monolithic silicon phototransistor detector in a dual in-line package.

Features:

Switching Speeds:
- 3 µs (Typ.);
DC Current Trasnfer Ration:
- 100% (Typ.);
Isolation Resistance:
- 1 TΩ (Min.);
Isolation Voltage:
- 2500 Vrms (Min.).