Getting TTL Logic values into the computer

ttl logic at serial port

Hi everyone, this is my first post, and I'll start by saying that I really don't know much about electronics. I'm more of a software man

As part of a University project, I'm making a device that can track the spatial position of a finger and display it on a computer program. The prototype is only going to be 1-dimensional tracking. I didn't think it would be very hard, but I fear I was wrong! I'm using LEDs mounted on a square frame, coupled with photo-transistors about 20cm away. The idea is that when a 'beam' between a LED and its associated photo-transistor is broken, the logic 1 is sent to the computer and displayed in the program I will write. If two neighboring beams are broken simultaneously, the software can show the finger as being between the two beams. I've attached a screenshot of the MultiSim circuit diagram, but I've just used switches instead of the LED/phototransistors.

Here's my big (unexpected) problem: How on can I get the logic values from the outputs INTO the computer? I thought it would be a simple case of purchasing some sort of microprocessor that takes the outputs from the circuit, and interfaces with the computer via USB (I don't have a RS232 serial port on my laptop!). But it seems that I'm going to have to purchase a microprocessor and program is myself with hardware programmers and assembly code and lots of other time-consuming stuff! Is this really the case? To read simple logic values into a computer, I have to do so much work?

I had one potential idea - buying a home alarm kit that can interface with a computer. The microprocessor's program would be perfect. When movement is detected, an output is 'switched' and the new logic values are sent to the computer and decoded for further processing.... Would scabbing the microprocessor out of one of these systems be sensible?

My main concern is that I just don't have time (with all of my other subjects) to learn how to program a microprocessor. I'm doing Biomedical Science, so I've never done anything like it. I can do the computer programming, and I can make the actual sensing circuit, but I can't get the information INTO the computer.

Any hints would be greatly appreciated. If you need me to clarify anything, please let me know.

Thanks in advance everyone!

c# ttl logic

There are several ways to do this. FTDI makes USB interface chips that do most of what you want. Take a look at:
**broken link removed**

If you are doing only a couple of prototypes, then you could also try using a USB to Serial converter and follow that with some TTL logic to form a parallel to serial shift register. The USB to Serial converters are now available in most electronic and computer stores for a very small price. Below is a link to a recent article along the same lines. The author is doing digital outputs rather than the digital inputs you want, but the concept is the same. I think he even has some example C# code. The beauty of this method is that the emphasis is on high level code on the computer which is your strong point and avoids using a microcontroller.

**broken link removed**