switching high inductance loads

[kitcat]

Hi.
thanks for those suggestions. I shall take a look real soon. I had been wondering what to do about my schematics. As for the schematics you mentioned, if you o have a chance could you have a look and see if you can find them. I am going to start again with this and see if I can't nail it.

Matt Kitcat

[mytekcontrols]

As for the schematics you mentioned, if you o have a chance could you have a look and see if you can find them

I found them, but it was part of a project I was subcontracted to do, so I can't post the entire schematic (too bad, since it has a lot of very useful power control related aspects). However I did take a snapshot of the item of interest, and have it shown here:

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=386">

The circuit shows an MOC3022 being used. This is actually a random crossing device. For zero cross switching, you will want to substitute a MOC3043 (unless you use the PIC to monitor the AC line for zero crossing as I did on this project). Here is the spec sheet for the zero cross part: http://www.jameco.com/wcsstore/Jamec.../277843FSC.pdf
These are about $0.59 each from Jameco, and will be a drop-in replacement for the MOC3022 device. The external triac can be anything that is suitable for the voltage and load you anticipate for your application.

The AC source can be any voltage you wish. Although if you want to run this at 200+ volts, it is recommended that the resistors be increased to 180 ohms. Also as I mentioned in an earlier post, you can directly drive small AC loads directly from the opto isolator's output (a very small relay or solenoid).

By the way here is the Zero Cross Detection circuit I was using on the original project:

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=387">

The output of the XOR Gate was monitored by the INT0 line of the PIC, and would enable switching of the OPTO's only when the AC was in the zero crossing state. I took this route because I was also doing speed control of 2 motors utilizing phase delayed switching, based on zero cross as the starting point.

I hope this info is of use to you,