How can I read buttons, k***s and switches and flip switches (control lights, buzzers) from software?

Question

I want to build a very basic security system (as a summer project - I don't have anything that needs protecting). I want software that can read input from a keypad or an RFID sensor as well as a door switch. I want to control a buzzer/siren and status lights.

I have a Mac on which I can run Linux (I'd rather not do Windows - an extra $200 I want to avoid.) My technical expertise is decent in terms of software - though it's all in the web app realm - my dad knows more about hardware-level electronics.

So... what kind of system can let me control and read switches for not very much money? Would I have to learn a new language (I know Python and a little Java - PHP also, but that doesn't seem relevant)?

Thanks!

Answer 1

the problem is not in the software, it's in the hardware. To read a switch's position (assuming a toggle switch) you usually need a separate set of contacts on the switch that you can connect to 5 volts. This 0v or 5v signal can be connected to a wire that can be read by an interface to the computer. In your case, probably via a USB bus interface.

similar techniques get you signals from other controls. Something that is not digital, like a k**b controlled potentiometer, such as a volume control is more difficult. You would have to put another pot ganged to the first, put a fixed DC voltage across it, and run the wiper of the pot to a A-D converter, which you run to the USB if. difficult.

Lots of other difficulties.

Which is why people who design instruments that are to be interfaced to a PC do the design with that in mind. Very difficult to retrofit an old design.

I'm out of time, try more later.

here is a USB IF, there are lots more around.

this one has 24 bits of control.

http://www.hobbyengineering.com/H3387.ht...

get this working and you are a long way there.

.

Answer 2

Simple way if you can use windows:  Use an x-10 computer interface to transmit x-10 signals over your house wiring to control devices.  I think it can also receive x-10 signals from external devices.

Check:  http://www.smarthome.com/1140.html

More complex way:  buy a LabJack U-3 USB hardware interface.  It comes with drivers for Windows & Linux which can be called from a Python script.  I chose this route and installed the driver on my Linux PC, but have not yet had the time to write the python program.  This is a much more versatile solution, but the LabJack device is somewhat complex and will take some time to understand fully.

Google "LabJack" to find out more about this device.