I run a dedicated Mach3-only computer , Xp-optimised, with a Breakoutboard.

With  Mach3  already started , i switch on the power to the breakoutboard.

Then i hear a electrical noise that makes my outputs  1,14,16,17 outputrelays  come on  and off
mostly with seconds interval but sometimes with a higher frequency.

It sounds just  like the earlier days parrallel printer initializing at switch on.

It Takes the system a fewl minutes to settle down, and then all is Ok.

As i use the outputs for spindle-control , i am looking for a cure....

PCs will do funny things with the pins on start up and shut down. Do you have a charge pump on the board you are using? You may want to do a search on Charge pump here and also look at some of the board makers sites for explanations.

Brett

Thanks Brett, i will first look in to that.

How do you power your relays. The best would be a direct drive from the PC - but it is not likely you would have the power.

I would suggest you use Darlington driver arrays. These are 8 circuits in a single chip. The inputs (which can be doubled up) are connected to the computer, together with one lead at 0v. There is a connection to the chip for the relay supply voltage. The outputs (which again can be doubled up) drive the 0v pins of the relays.

The 0v to the chip must have a direct path back to the computer, so that when the computer is turned on the 4 output signals have a 0v to refer to, and therefore set the following circuitry.

I would suggest that your problem is in the breakout board wiring, in that the signal ground wire from the computer is not making a direct contact with your driver circuit for the relays. This means that although you (correctly) start up Mach 3 first, the signal to the relays is not fixed, in that the supply voltages to your driver circuit do not come on until you switch on the breakout board.

After that, it takes a little while for the relays to pick up the driver voltage and settle.