🚀 go-pugleaf

In article <845933481.19107.0@intra.demon.co.uk>
           paul@intra.demon.co.uk "Paul" writes:

> I am looking to switch on/off various pieces of equipment by writing
> software routines to interface between the com port and the equipment.
> 
> I have noticed when I open the com port the voltage across certain pins
> increases from zero volts to 20 volts. Is there any way of utilising
> this voltage increase to 'control' equipment.

Yes these can be utilised for controlling things like cassette recorders, 
especially the battery operated ones. You will need to provide some interface 
buffering between the com-port and the cassette recorder. If you are using the 
cassette recorder for data storage (good o'l Kansas style) then the whole 
interface could take account of the control needs.
 
> Initially I am just looking to switch on/off a 6V cassette recorder but
> eventually I would like switch on/off some 3 phase (330V) stepper
> motors.

Controlling high voltage stepper motors presents a whole different set of 
problems. In order to maintain a safe system you will have to consider the 
requirements for isolating the computer equipment from effects by such 
hazardous voltages. Also for consideration, and in view of the likely torque 
that such steppers will have) is the physical safety aspects of the system. It 
would not be a good idea to have such a stepper controlled from a PC directly. 
Far better would be the design and construction of a separate stepper motor 
controller which had built in features that ensured the motor could not be 
used in unsafe circumstances.
 
> I have seen the 64 channel i/o controllers as advertised by Maplins at
> 80 but I have no real idea how they work. What are 64 channels needed
> for ?  It appears that other hardware is also required, like relay
> boards. The relay boards at 120  appear to only operate at relatively
> low power consumption (120V 2amp). Surely there must be some cheaper way
> of getting a PC to switch on/off a cassette recorder than 200.

Switching on and off a cassette recorder should only set you back about UKP10 
to 20 (including boxes). The 64 channel device could be useful for running 
things like Lego models with multiple motors, autoimating the train set. For 
anything that is serious control then better parts are available which will 
guarantee the Safety Integrity of the system when used in accordance with 
manufacturers instructions. Where Safety is important (most control projects) 
then do a risk assessment first.

-- 
Paul E. Bennett <peb@transcontech.co.uk>
Transport Control Technology Ltd.
+44 (0)117-9499861
Going Forth Safely