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Subject: Re: Triac???

Date: 02/03/03 at 3:35 PM
Posted by: Brian Snell
E-mail: bsnell@lara.on.ca
Message Posted:

In Reply to: Triac??? posted by Geoff on 01/31/03 at 5:57 PM:

Hello Geoff.

Your E-Mail description is somewhat helpful but I am lost when trying to work out that your "single" (presumably "signal") will come from your motherboard but is then routed to your device to await either one of two selectable additional signals being initiated. Why not just include the desired final action command from the motherboard in the first place. My query re interface port was to find out if you already had a dedicated "external peripheral" control arrangement or not. You list a serial and a USB port for your computer but no "parallel printer port". By using a parallel port as an output source, all sorts of signals are available from the motherboard simply by selecting any printable keyboard character to "print" and decoding its corresponding pin on the parallel printer cable. These printer-coded signal are very short but can be "captured" by an external interface circuit and used to control whatever. If you wish to control 24 volt motors these could be switched via a triac which could be triggered by an opto-coupler, such as an MOC3011, which in turn would be enabled by the decoded "print x" signal.

There are a few points which require clarification. The triac is a bi-directional switch designed for full-wave AC control, so if your motors are run from 24 volts A.C. a triac would work O.K. but would require a "pulse-stretcher" to extend the duration of the controlling "print" pulse until whatever cycle driven by the motor has elapsed. If the motors are run from 24 volts DC then use an SCR (unidirectional switch) which becomes self-latching in the "on" position after receipt of an initial trigger pulse. In this case, some form of "de-latching" would be required -- probably the easiest would be some form of microswitch actuated from some portion of the mechanism driven by the motor when the mechanical cycle has been completed. There are also a few potential problems with electrical transients, and/or false triggering, produced when the motors are switched and also while running, but these can be corrected by appropriate filtering and careful design.

If you would indentify whether your motors are AC or DC, and confirm whether you have available a parallel port, then this would be a start. It would also be helpful to know if you have electronic-assembly skills and can understand circuit-diagrams, as it would appear that you will need to put together some circuitry in order to implement your desired operation.



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