SC403 is an SC400 series digital I/O module for the I2C bus.

This module houses a MCP23018 and provides 16 quasi-bidirectional input/output lines. Each I/O line can be driven low by the MCP23018 or pulled low by an external signal. The state of the I/O lines can be written and read by an I2C bus master.

The I2C device address is set by a voltage normally generated with two resistors. The default address only requires a single wire link instead of the resistors.

The device slave address (7-bit) is: 0b0100AAA, where AAA = three address jumpers.

The recommended (default) slave address (7-bit) for SC403 is: 0b0100000, 0x20 (R3 = not fitted, R4 = wire link)
The address bytes are: 0x40 write, 0x41 read

Downloads

• SC403 – Kit contents sheet (PDF)
• SC403 – Printed circuit board Gerber files
• SC403 – Schematic v1.0 (PDF)
• Example code: see SC400 series details

Suppliers

• SC403 – Kit (Tindie)
• SC403 – PCB (Tindie)

Parts List

Reference	Qty	Component
PCB	1	SC403, v1.0, PCB Design at OSHWLab
C1	1	Capacitor, ceramic, 100 nF
P1	1	Header, male, 2 row x 6 pin, angled The second row of pins needs to be removed.
P2	1	Header, male, 1 row x 6 pin, straight
R1 and R2	2	Resistor, 10k, 0.25W Optional
S1	1	Header, female, 1 row x 6 pin, angled
P3 and P4	2	Header, female, 1 row x 10 pin, straight
P5	1	Header, female, 1 row x 3 pin, straight
R3	0	Not required for default address
R4	1	Wire link (eg. resistor leg)
R5	1	Resistor, 10k, 0.25W
U1	1	MCP23018
U1 socket	1	28-pin DIL socket, narrow (0.3″)

Assembly

This design is so simple it does not justify a detailed assembly guide. Just assemble according to the photo above.

In order for the daisy-chained PCBs to be a consistent level, header pins (P1) need to have a profile that matches the socket (S1). By far the most common angled header pins do not match. A suitable profile header can be created by removing the second row of pins from a double row header. The pins can easily be pulled out of the plastic guide with a small pair of pliers.

The two resistors, R1 and R2, are not normally required. These are pull up resistors for the I2C bus signals, serial clock and serial data. The pull up resistors typically found on I2C bus masters are usually all that is required. However, should you require additional resistors for any reason, they can be fitted here. The most likely reason to add resistors is to terminate a long bus with many devices connected.

The I2C device address is set by a voltage normally generated with two resistors. The default address only requires a single wire link instead of the resistors. Fit a wire link, such as the offcut of a resistor leg, in position R4 and do not fit anything in position R3.

Notes

• This product is designed for hobby use and is not suitable for industrial, commercial or safety-critical applications.
• The product contains small parts and is not suitable for young children.