06-21-2002, 11:18 PM
I had this idea today while I was driving home today and I wanted to see if it is possible. Lets say I have Electric Solinoids that are powered by a 12v signal.When 12v hits the solinoid it activates once 12v stops it closes. Is it possible to send this signal from the serial port on my computer, using vb to activate then stop the twelve volts?
thanks for any input?
06-22-2002, 03:02 AM
I'm not 100% sure of this but I think the serial ports have 5V potential difference, so they could not drive it directly. You could, however, use it to switch a relay or a transistor and run the 12v through that.
06-22-2002, 03:31 AM
Not only that, but the actual current carrying capacity of the serial port is quite limited. A solenoid takes quite a bit of current....probably enough to blow your serial port....
Again, the solution is to use the serial port to trigger a low current relay.
06-22-2002, 12:54 PM
So technically if I used a relay, this is acctually possible.
Thanks a lot for the replys.
06-22-2002, 01:11 PM
The normal voltage on an rs232 control line is usually 10 or more
volts, but as Bill said, there just isn't enough current. It might
work with the low current relay, but to minimise the possibility of
blowing the uart chip, a solid-state buffer like Banjo mentioned
would be safer. Having not done any of this stuff for 20 years, I
don't even know what kind of chips are out there now.
07-01-2002, 07:28 AM
As the others have alluded to the fact that the serial port does not have much current driving capacity, you'll want to use a simple one transistor circuit to drive the relay. You can use an RS-232 port handshaking line to toggle the relay through the driver circuit. This way, you still have the use of the RXD and TXD to do serial i/o.
E-mail me if you'd like more details and a schematic.
BTW, the serial port voltages are +12v for a low
and -12v for a high (note that the logic is inverted).