Programmed relay on PCI card in computer, need to bypass the bus?

[co88dy]

Sorry, I am not an electronic engineer but I do use eng-tips sister site tek-tips for telecommunications, but it looks like I need some eee assistance.

I attached a diagram showing what I have. To put it in words, I have a computer with a PCI card, that has a DB 15 port, that can be programmed as a relay. The relay is normally open and when a condition happens in the software it closes to power a light. All of this part works, except for one issue. The bus on the PCI card only supports 150mA and the light requires 400ma to power on.

I wanted to see if there is any premade device, or an idea on how to make something that will still use the computer relay for the software condition, but will pass the power down a separate circuit, bypassing the PCI card. I was think a device that detects continuity from the pci card, and opens or closes another relay when continuity is lost or detected.

Sorry for my lack on knowledge, and information would be appreciated.

 

[IRstuff]

USB supports 0.5A, but I don't understand the bit about the PCI card?

How is its bus limiting the current?

Why not run power outside of the PCI board?



TTFN
faq731-376

 

[SceneryDriver]

Since your drawing appears to show a power supply external to the PCI card, I'm going to assume that it is either a low-current relay contact, or low current transistor output. In either case, simply have the PCI card's output switch the coil of an external relay. That relay's coil should have a compatible voltage - 12vdc will probably work, as that's what you show in your drawing - and the contacts should be rated to carry the current of your load; 400ma is a tiny load. The relay linked to below has contacts rated for 15A.

Below is a relay that should work, given the limited info you have provided about your PCI card.

http://www.automationdirect.com/adc...81_-z-_782_-z-_783_-z-_784_Series)/781-1C-12D

A solid state relay would work as well. Pick your "coil voltage" and "contact voltage" appropriately to control your load.

Whatever relay you choose, be sure to provide a freewheeling diode across the coil to prevent an inductive spike from damaging your PCI card output. Note: if you choose to use a solid-state relay, the diode is not necessary.

Do yourself a favor and buy the socket for the relay. it makes it SO much easier to connect.


-SceneryDriver

 

[co88dy]

I need to use the PCI card so the software in the computer can tell the relay when to close, and send power to the light. I did consider using usb, but I am not sure how to program the software to do the same as it does off the PCI card. To give you more information about what I am doing; the computer is being used as a phone in a 911 dispatch center. They want a light to come on whenever they are on a 911 call. The only problem with this I have encountered is the power differences between the bus and the The technical specs of the the pci card which contains the relay, claim it can only handle 150ma at 24v. When the relay in the PCI card is closed it uses the bus on the card to connect the in and the out. Also I did try putting connecting a 12v 1A power supply to the setup and it turned the light on, but within seconds I could smell the pci card smoking, so I unhooked it.

Another question, if I were to use a the 12vdc by 1A power supply, and I run the hot lead straight to the light, which draws 400ma, how much power would be coming down the return. By this I mean, can I run the hot lead straight to the light, and put the return through the relay?

 

[IRstuff]

Do you have access to the software code?

Otherwise, you'll need to do as SceneryDriver suggests, which is to use the outputs you currently use to drive a relay that, in turn, drives the light. Note that you'll need the external power supply to do that. Note also, the relay cited requires 0.7W DC, which might still be too much for your board. Something like [URL unfurl="true"]http://www.digikey.com/product-detail/en/G5T-1A%20DC5/Z2774-ND/1731474[/url] might be gentler on your PCI board; it only takes 5V, 40mA to engage the relay.

TTFN
faq731-376

 

[itsmoked]

If you have 150mA available just use the correct light - A LED stack light! It will never burn out, you have no relay, no noise, the light will be nicely finished.

http://factorymation.info/catalog/fmcat_towerstacklights.pdf

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LiteYear]

Another question, if I were to use a the 12vdc by 1A power supply, and I run the hot lead straight to the light, which draws 400ma, how much power would be coming down the return. By this I mean, can I run the hot lead straight to the light, and put the return through the relay?

Nope, the full 400mA will be flowing in both leads so there's no tricks to get you out of trouble there. As SceneryDriver says, you need a cascading relay. Your PCI card's relay is hooked to the coil of the second relay and the second relay (appropriately rated) closes the light circuit. Note that you'll need to run your PSU in series with the coil of the second relay, as well as the light circuit.

By the way, as a courtesy to others, please consider using PNG for diagrams instead of JPG. The 'P' in JPG is to do with photographs - it really isn't well suited to diagrams. Your attachment was 2.5MB, which everyone that wants to help has to download individually. Compare to the attachment to this post, which is the same diagram as a PNG but comes in under 10kB.