Raspberry GELI

This is the expansion board designed for the Raspberry Pi. 

Detailed specification is below but in summary :-

– 8 Digital Output/8 Inputs/ 8 Status LED’s – Link Selectable

– 8 Bi-Directional Digital IO

– Upto 8 Analogue Inputs – 8 Bit Resolution

– Upto 2 Analogue Outputs – 8 Bit Resolution

– DC Motor Drive two channels

– Serial Interface with ( RS232) Level shifter for connection to PC/Terminal

– RTC Clock with battery Back Up

– 1-Wire ( Dallas/Maxim) Interface

Current Status

GPIO Expansion Board PCB complete and working,  now writing code using Java, JNI and some hacked C from the Wiki.

GPIO Expander and Lab Interface (GELI pronounced ‘jeli’) Spec

1.       Overview

The GELI provides a developer, experimenter with real world interfaces on a single 150*100mm PCB. Connection is currently by 26 way ribbon cable but could change depending on the RPI header.  Digital,  Analogue and high current interfaces are provided along with a prototype area.  In addition to real world interfaces the GELI provides a buffered asynchronous (RS232)  for TTY/COM connections to an external PC/dumb terminal as well as on-board Real Time Clock with optional battery backup.

The GELI has been designed to enable developers/experimenters to connect up to the real world using readily available low cost components as easily as possible.  The board has been designed with all almost all components

2.       Digital I/O

Buffered Digital IO – individually selectable by jumper directly from RPi GPIO Connector

a.        8 Outputs

Single buffered to 3.3V logic direct to Header, these are further buffered and connected to LEDS and can be connected by links to DC Motor PWM Drive (L298)

b.       8 Inputs

3.3V logic inputs, buffered and current limited to limit possible damage to RPi

– I2C Digital IO – 8 Input/Outputs – (PCF8574) and presented on header

3.       Analogue IO

Interfaces to external analogue sensors is implemented by use of two PCF8991 ? Analogue Interface over the I2C bus.  Each device provides 4 Input and 1 output channel.

a.        Analogue Input ( 8 Channels ) – 8 bit resolution , channels can be reconfigures for single ended or differential operation , see PCF89991 datasheet. Max input voltage 3.3V.

b.       Analogue Output ( 2 channels) – Single Ended 8 bit resolution – 3.3V Max Voltage

4.       Motor Drive

Single L298 DC Motor controller.  This L298 device consists of two separate channels and the GELI enables the single PWM signal to be fed to either ( or both of these channels.  The L298 can supply up to 1A feed to 32V,  the power feed for the DC motor controller is physically separated with connection only for logic supply of 5V and 0V.

5.       Real Time Clock (RTC)

A Maxim DS1307 Real-time Clock device , with optional battery back-up, provides real time and data functionality even when power is not supplied.

6.       One Wire Interface

The Maxim/Dallas 1-wire protocol provides access to additional device types such as Timers, Temperature Sensors and A2D convertors.  The 1-wire interface is accessed via the I2C bus.

7.       Prototype Area

A small prototyping are of 0.1’’ ( 2.54mm) spaced pads has been provided to enable additional devices e.g. sensors,  signal conditioning or microcontrollers

8.       DC Regulator

A single 3.3V regulator provides the capability to power the GELI board from an external 5V supply.  User selectable links guarantee that the GELI gets it supply form eithere the RPi or the external supply but not both.

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