Re: [CAD_CAM_EDM_DRO] Re: Getting Parallel port to run relay

bertmantx wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, codeSuidae <codesuidae@c...>
>wrote:
>
>
>>bertmantx wrote:
>>I would not recommend trying to run the relay on power from the ports, they aren't intended to supply that kind of current. Instead use an external power source (a 5ish volt battery is fine for testing, or grab a 5v supply line from inside the computer).
>>
>>
>I thought I understood that Pin 1 on serial port was direct path to comp. power
>
>

Presuming you meant to write game port, yes, it is, but I have no idea
how much current it can supply. Feel free to use it, but keep an eye on
it for a while to make sure its stable.

>>Your transistor circuit is the correct way to handle the relay,
>>
>>
>
>Is NPN proper style of xsistor??
>
>

In the configuration you are using it, yes. If you are using something
like a PN2222A you might need a fairly stiff drive current to saturate
it, Hfe can be anywhere from 30 to 300. A 1k or even 500 would be worst
case.

>>you'll need to connect the coil to an external power supply.
>>
>>
>I assume that external and internal grounds will have to be common
>right?
>
>

Yep.

>Shouldn't the circuit have fired with 5v power source going directly
>to Base? Or does it have to be current reduced with resistor?
>
>

If your voltage is high enough to reliably trip the relay (about the
best you'll be able to do with the transistor is 4.3v), and the
transistor hasn't been destroyed by excessive base current, then yes.
Whats the coil resistance for the relay?

CS