National Instruments DIO 24 Digital IO card to utilize steering wheel control
Sorry for a long winded post, but since this is THE "hardware development" sub forum, I thought I'd better explain where I am coming from...
A while ago, I wrote a very simple Visual Basic application that utilizes National Instruments PC-DIO-24 digital IO card. I am not an expert in VB, but the task was simple enough so I was able to write the program.
Anyway, this is the card.
I bought a used ISA version for $20. Before you bash me with the ISA, there are PCI and USB version of the same card. My question is more fundamental than choice of the bus.
My VB software basically worked as a switch panel interface. It was for an industrial machine control. The operator panel has 20 or so buttons, and I had to "Map" those buttons to the control "Buttons" in the VB application.
While planning for a CarPC, I thought, if I re-route wires from Steering Wheel buttons, Headlight switches, Reverse gear line, etc etc, then I can "MAP" the control to the front end. Then I will be able to control Volume, FF/REW, Audio Mode, RearView Camera, Night Dimming etc.. I can probably add a toggle switch or momentary switch as a Mute button or curser control keys... options are endless......What a great idea.... so I thought.
Then..... this PC-DIO-24 has 24 channels of I/O... i.e., It outputs too.... I can configure it to have 16 inputs and 8 outputs... If some how I can get this card to trigger a 12V relay, I can control car's functions like sunroof, window, HVAC, Remote turn on of the Amplifier to prevent thump, interior lights, etc etc....
Ok. So that was long winded introduction. Here's the real questions.
According to the spec sheet, this card can output 5 Volts @ 2.5mA. Basically a state "LOW" is 0V, state "HIGH" is 4~5 Volts, and it can deliver 2.5mA.
So here's my question to you Electronic Gurus.
1. I don't think there is a mechanical relay that can be pulled reliably with this kind of power. Correct?
2. If my assumption #1 is correct, then I'll have to drive a smaller relay (which trigerrs with ~3mA) to trigger a bigger relay (that can carry 12V@20A). Correct?
3. Then what "small" relay should I use? Solid State relay? Opto-Relay? What relay can I safely use here? I understand I might have to have a 5V power rails... but I can take that from the PC's PSU.