DAC Circuit Board - User Guide

Introduction

Thank you for purchasing the Classic Flight Digital to Analogue Converter (DAC) circuit board. We hope that you will find that it is a simple and effective tool for use in your motion platform. It has been designed to fit in well with the rest of the components in the drive control chain.

We have tested the circuit board extensively and derived the accompanying guidance from our motion base design, building and testing. However, we cannot be responsible for any loss or damage arising from use of our DAC board, or the guidance set out in this or any other documents released by us.

This guide assumes that you have already purchased, installed and configured Motion Drive software on your PC. In order to install and calibrate your DACs, you will need to have Motion Drive or a similar software package installed on your PC, together with the suitable USB devices, such as the USB modules provided with Motion Drive. If you are using a motion software programme other than Motion Drive, you should still follow the instructions given here, but you will need to refer to your software user guide to find out how to carry out some of the steps.

If, after reading this documentation, you have some questions regarding your particular application, please contact us.

Essential Information
Care and location of your DAC boards
Storage. The DAC boards are a delicate item of electronic circuitry. They are supplied to you in special anti-static protective wrapping and should be kept stored in that wrapping until ready for use in a clean dry place.
Location. They should be located in a suitable place on your motion base, where they will not be subject to physical or electrical damage, preferably firmly fixed inside a suitable electrical enclosure box of the type that can be purchased from component suppliers.
Installation. When handling and installing the boards, you should take care not to incur damage through careless handling and static electrical discharge. Make sure you use a suitable earthing method on yourself before and during handling. When connecting components (USB modules, other boards etc.), ensure that the boards are NOT powered up by disconnecting the USB modules from the USB port of your PC.

Functional Description

The function of a digital to analogue converter circuit is, as its name suggests, to convert digital signals that are input to it into analogue signals that are then output from it. Our DAC board is no different.

The digital signals are generated by the Motion Drive 3.0 software and transmitted from your PC via one of the two USB modules provided in the software package. For the DACs, USB module #1 is used to receive the signals from the PC. The signals are then transferred to the DAC via one of the three ports on USB #1. Which port is used depends on which drive the DAC is working.

The signal is transmitted as an 8-bit binary word - a value in binary between 0 and 255. The value of the word that the DAC receives varies with the strength of the signal that the PC is sending. It also depends on whether the PC and DAC are running in unipolar or bipolar mode (see below).

In addition to the binary word, the DAC has one other input. This is a control pin signal in the form of a logic high or logic low signal. This signal is used by the DAC as an instruction to act (see below).

The digital signal is converted to an analogue (continuously variable) control voltage by the array of microchips and other components on the DAC board. It is then available as an output to be sent further downstream in the drive control chain. Nearly all forms of drive controller - electric motor, hydraulic or pneumatic actuators - require an analogue control voltage to provide a variable output (motor speed, actuator force). There are a few exceptions e.g.DC stepper motors. So for the vast majority of motion platform designs, some kind of DAC will be needed.

Unipolar and Bipolar modes
The DAC has been designed not only to fit in with the USB modules and Motion Drive software, but also to work with a range of possible drive controller devices. You may have chosen electric, pneumatic or hydraulic drive actuators for your platform, and they will have their own requirement in terms of the analogue drive signals as their inputs. Some drive controllers want control voltages that run from 0v upwards and some that run from a negative voltage to a positive one. The Classic Flight DAC can provide either of these, as can the Motion Drive software.

Voltages that run from 0v to some positive figure are said to be unipolar and when sending that kind of output, the DAC is working in unipolar mode. Volatges that run from some negative figure to a positive figure are said to be bipolar, and the DAC will working in bipolar mode when sending that kind of output. The Classic Flight DAC will send out control voltages either in the range 0 to +5V when in unipolar mode or in the range -2.5V to +2.5V when in bipolar mode. You are able to sleect in which mode the DAC runs.

Control signal
The control signal input to the DAC is a simple logic high or logic low on one of the pins from USB module #2. The DAC responds to the state of that control signal as its instruction to what it should do. When the pin is low, the DAC is open to receiving a new 8-bit binary word value through the main input. When the pin is made high, it instructs the DAC to convert that last signal into an analogue out voltage, and to keep sending that voltage until a new 8-bit word is received. So, each time that you want to change the ouput from the DAC, you need to take the control pin low, then send the new 8-bit word, then take the control pin high, which initiates the conversion into analogue.

Of course, all this instructing takes place at very high speeds, so the appearance at the output of the DAC is of a continuous voltage, which varies in steps as the software demands.

Having covered the overall functions of the DAC, we can move on to connecting the board and calibrating it.

© Active Simulation Limited 2007

DAC circuit board User Guide version 1.0