Electronic – What are the ways I can make the circuit communicate with a computer

communicationwireless

I am a novice at electronics hacking. I would like to know how I can make a circuit communicate with a PC. Take for example, a simple circuit, with one LED and a switch. The switch on the circuit however, is not used to control the LED. Pressing it communicates the present state of the LED. I have a program running on my computer, which has for an UI, a button and a graphic object; a black filled circle.

I should be able to turn the LED on and off from my computer by clicking the button on the screen.
Pressing the switch on the board, should communicate to the program the state of the LED. If the LED is on, the black circle should turn green, else it should turn black.

This a hypothetical situation I have described to explain the problem. I am not looking for a solution to implement this thing, but want to know how this communication between my circuit and the computer can be achieved, in a simple, inexpensive way, over

wire?
wireless?

And if you could suggest where I should look and what I should learn to get started with my electronics project, that would be of great help.

Best Answer

There are quite a few different ways you could achieve this. Here are a few:

You could program a small microcontroller like a Microchip PIC16F84A to watch the button and the LED. Whenever the button is pressed, the PIC16F84A sends a character through a FTDI serial chip to a USB port on your computer. On your computer, a program written in Processing watches the USB port and updates the pictures on the screen. Total cost: $20 for some chips and a breadboard.
You could buy a Bluetooth Arduino with a prototyping shield. The Arduino talks over a Bluetooth chip to a Bluetooth card in your PC. A program written in Python listens to the Bluetooth card and draws the appropriate picture on the screen with the Pygame library. Total cost: $150 for a Bluetooth Arduino.
You could attach a webcam to your PC that watches your LED and the button. A program written in Ruby is analyzing every image coming from the webcam, comparing it to the previous image. When it detects a change in the region of the image near the button, it looks at the color of the pixels in the LED region and updates a value in a database. A webpage auto-refreshes using the jQuery timer plugin, and updates an image on the screen based on the value in the database. Total cost: $25 for a crappy webcam.
You could find an old PC with a parallel port and install Ubuntu Linux on it. You connect the LED and the button to pins on the parallel port and then write a program in C that reads address 0x378. Based on the data returned, it makes calls into a C graphics library that does the appropriate screen drawing. Total cost: free, if you can find a PC old enough.
You replace the power button on your computer with the button in question, and the power LED with the LED in question. You replace your BIOS with a version of OpenBIOS that has been modified to display a green circle on the screen, and never boot any operating system. Total cost: probably the cost of a new PC.

But in all seriousness

I think I'd recommend an Arduino and Processing. They're simple and great for beginners. Total cost: $30 for the Arduino.

Best of luck.

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Electronic – Simplest remote IR

Phototransistor configured as an inverter:

5V ----+
       |
       /
       \  47k
       / 
       |
       +----- Logic output (inverted)
       |
  \   /
  \  |    NPN
      \>  Phototransistor
       |
      ---
       -

A phototransistor is like a photodiode, but has a significantly increased gain. So when light shines on it (or IR, if it has an IR filter) it will pull down the output, conducting a few mA. A photodiode could do the same job, but you'd need a much greater (x100-1000) resistor, and this might be overwhelmed by the any load impedance.

You could put another inverter on the output to get a logic signal of the correct polarity (or to buffer it, as it won't take much load current.) Here is one possible inverter circuit:

          5V ----+
                 |
                 /
                 \  10k
                 / 
                 |
                 +--- output
                 |
          10k   /
Input ---/\/\/--|   NPN
                \>  2N3904
                 |
                ---
                 -

Electronic – the cheapest way for two devices spaced less than 10 feet apart to communicate wirelessly with each other

I'll assume you want to do this wireless, otherwise the solution is obvious.

I would go for infrared. The transmitter can be a small microcontroller sending a pair of bytes to an IR receiver module.

These receiver modules are tuned to a particular protocol. You can use an RC-5 module; RC-5 transmits 14-bit at a time using Manchester encoding. You can easily add a pair of bits to it, and define your own codes.

A 3 m range should not be a problem. I've used Vishay RC-5 receivers at 15 m range. At shorter distances you probably won't even have to direct the LED to the receiver. In a normal size room the signal will reflect off the walls.

A cheap RF solution is the RFM70:

enter image description here

Less than 5 dollar at Digikey. That's far less than an Xbee.

Best Answer

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