HobbyCNC controller spindle control?

[PranksterO]

I have a HobbyCNC 3 axis controller board with turbocnc running my cnc setup. I wanted to be able to have the computer control the spindle on/off actions. I read a few posts and found out that controlling the spindle is pretty simply set up with a 5v relay connected to (in my case) pin 17 on the parallel port and then ground. The problem is my relay isnt kicking over. It seems not to be getting the full 5v required to throw the relay. Anyone have any ideas?

[wjbzone]

How are you checking your relay? I thought my relay was not working when I was just checking continunity across the 120v side with a volt-ohm meter.
When I put a load on the 120v side it worked. Hook up a light bulb or your router and try it.
Bill

[PranksterO]

I know my relay isnt working because when I apply a battery to the relay I can hear it clicking over. I have also checked it on a volt meter. Seems that the parallel port isnt providing enough juice to throw my relay.

[wjbzone]

How many volts is your parallel port? My relay is rated to turn on with 3.5 volts.

[PranksterO]

I thought the parallel port provided 5v? I dont really have an accurate voltmeter avalible but I could probably safely say that it's below the 5v required by my relay. Is there anything I can do that will be easier that just buying a new relay? If I do need a new relay where whould the best place to be to get a pretty cheap solid state relay with a lower voltage?

[rustyolddo]

Just a note, the parallel port is designed to sink current not source it. Chances are your relay requires more current than the port can supply. Here's the data for the port:


Data output (>2.4V)...........2.6 mA
Data line sink (<0.4V).........24 mA
Control output (>2.4 V).......0.5 mA*
Signal lines (short circuit).....1 mA
Control line sink (<0.4V)......7 mA

So, if your relay requires more than 2ma @ 3V, you won't get a closure. You can use an electronic switch or opto isolator and a seperate 5V p/s which would be the recommended way of doing it. If you do power the relay from the port directly, be sure to use a snubber diode to keep the back EMF from potentially damaging the port.

Edited to try & fix formatting.

[ljoe1969]

tell me how to hook up this "snubber diode" you mentioned.