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MeccanIC Controllers, a
preliminary discussion.
The controllers run the motors and interact with the I/O signals.
The  concept of the levels of control.
The Concept of Levels for the Controllers
and some preliminary ideas


If we subscribe to a system of
"levels of sophistication" in our system it will make our lives easier.

If we decide that the controllers must be able to be
daisy chained it will mean that each controller can be smaller and each one has to have a unique eight bit (one byte) address.  Though doing this will make each controller smaller each one will cost a bit more in that we have to have a processor, memory etc in each one now, i.e.  we will be repeating some components in each controller.  Still this approach has its advantages.

(For now let just us say that all controllers can be daisy chained in
any combination of and level controllers other than level 0 because they do not respond to computers.)

I think each controller should have the ability to run
a minimum hardware configuration that we agree on.  What should that minimum configuration be.  I.e. two motors, 4 switches, 6 relays! etc. etc.  (It will be whatever we decide,  below are some preliminary suggestions.)

To date I have not been sold on the idea of the Lego type controller into which you can download a small program.  We want to be able to build machines that are
much more sophisticated than that.  Just like there is not limit to what you can build with Meccano there shoud be no limit to what you can add to the electronic and electrical capabilities with MeccanIC.  Ambitious yes, impossible no.



Basically what do controllers do?

Basically controllers run motors, turn output switches on and off and report when external switches are turned on and off to the controlling computer.  The computer interrogates the controller frequently and also tells it what to do with the motors and the output lines.  It does not control the input lines (external switch conditions).  The rest is what you decide the machine has to to and how you do it.  Software.

The following requirements must be met by all controllers:
Maybe: Require only 1 power supply (at 12 or 24 VDC regulated).  All motors will be 12 volt motors that are run on 24 volts through a PWM or analog system so there is some advantage of going with 24 volts as the standard power supply.
5 volts generated internally. 12 volts generated internally if needed.
Have one RS-2323 serial interface (or we might want to use the new USB Universal serial bus standards),
Must allow daisy chaining to next controller
Have terminal strips for all wires (no soldering allowed anywhere on controller. This is necessary so the controller will last longer)
Handle all overloads automatically without blowing up.  Fuses or electronic shut off.
Have internal self check capability with Green LED indicating OK condition at each startup.
All high voltages shall be isolated and made safe at the power supply provided meaning at the wall socket at the plug and "not at the controller".  In the US any voltage higher than 24 volts has to be in metal conduit.  24 Volts is considered the top end of low voltage and is used extensively in industrial controls.  If the European standards are different from the above that has to be considered.

Level 0 devices
Level 0 is the bottom level.  All low leved devices can be used without a computer or a controller.
ON-OFF switches are level 0 devices.    They can be
used without a computer. 
Simple motors are Level 0 devices,. 
They can be turned on and off with the level 0 switches.
Later on these devices must be able to be added to a higher level controller. 
At each level, the manufacturer can of course provide more than what the standards provide.  Standards are the minimum requirement.
The basic idea is that all lower level devices can be used at all higher levels so that there is no obsolescene built into the system.  The investment you make is always viable.

Level 0 control
Toggle switches etc.
Simple DC motors
Reversable PMDC motors with or without gearbox.
Microswitches
Relays
No computer is used. 
Example: A motor runs until it trips a switch that turns it off or maybe reverses it though a relay.  Motor speed only is controlled through a Level 0 controller. 

Level 0 controller proposal.
Level 0 controllers are controllers that
do not use a microprocessor or interact with a computer.  They control the speed of the motor only.
Power supplies are not provided with any level 0 controllers. 
The DC power supply selected by the user needs to match the needs of the motor to be controlled and does not need to be a filtered power supply.
Each controller is provided with an external potentiometer that can be located remotely from the controller to provide speed control.  
The potentiometer shafts are the standard Meccano size so all Meccano parts can be mounted to them. 
PMDC motors are preferred for all applications and are a must for reversing applications with these controllers
.

Level 1 controller proposal

A level 1 controller has the following capabilities.
It has a one byte address that can be set to any number from 1  to 16
It can communicate with a PC, Wintel of Mac
Control 2 Simple level 0 DC motors
It can reverse the motors
It can control the PWM speed of the motors
There is simple feed back from switches but none from motors.
It can power two small relays or they might be transitors. (Needs more thought because I cannot think what to use these for off hand at this level of sophistification.)
It can read 8 switches
Switches can be microswitches
Toggle switches
Momentary contact push buttons
Magnetic reed switches
The output contacts of a relay
It cannot read or output TTL signals directly.
It can control 8 LEDs.  These provide visual feedback to the user.
The LEDs are captive on the controller card.
2 yellow, 2 green, 4 red.
If you want to control 4 motors you daisy chain a second controller to the first one. And so on.

Next we control two stepper motors

Level 2 controller proposal
A level 2 controller has the following capabilities.  It can
Communicate with a PC Wintel of Mac
It has a one byte address that can be set to any number from 1  to 16
Control 2 Stepper motors
There is no feed back but position and speed can be controlled
It can read 8 switches
Switches can be: 
microswitches
Toggle switches
Momentary contact push buttons
Magnetic reed switches
The output contacts in a relay
It cannot read or output TTL signals as now proposed
It can control 8 LEDs
These provide visual feedback to the user.
The LEDs are captive on the controller card.
2 yellow, 2 green, 4 red.
It is very useful to be able to read on potentiometer or two. (Meaning that the position of the potentiometer in a machine can be used to make the computer do all kinds of things besides changing the speed of a motor.)


Next we control 2 Servomotors
add a 2 line by 16 character display
Level 3 controller proposal
A level 3 controller has the following capabilities.
It has a one byte address that can be set to any number from 1  to 16
It can Communicate with a PC Wintel of Mac
Control 2 Servo motors with encoders
full feed back and speed control
It can read 16 switches
Switches can be microswitches
Toggle switches
Momentary contact push buttons
Magnetic reed switches
The output contacts in a relay
It can read and output 8 lines of TTL level signals
It can control 8 LEDs
These provide visual feedback to the user.
The LEDs are captive on the controller card.
2 yellow, 2 green, 4 red.
It can output to a display
2 lines of 5 x 7 LED matrix
16 characters each line

Level 4 controller proposal
Suggest that there be no limit to what features can be
provided by the manufacturer in a level 4 controller
It would be useful if it had to have all Level 3 functions supported.
And it does have to meet the general software requirements if it is to be a
MeccanIC compatible device.  But we leave it  to the manufacturer.

Level X controller proposal
Level X controllers are controllers that interact with
Meccano and maybe MeccanIC electronica  but do not meet our specifications or obey the MeccanIC language.


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09 Apr 04