I found this cool article that might help with some out of the box ideas, of course with this you will save a lot of money but it will be a lot of work to make it work for your application.
one of the things will be trying to direct the light from your CB Led. i am thinking if you make a set up like the one described below using a LED to detect light, you will need to build a housing for it so you can mount a fiber optic to it.
either way i found it interesting. i copied a link and the text from the article below describing how to use a led to detect light.
Also if i were to do this and needed a reliable check i would use a vision camera, there are many different types and they are not cheap but you might be able to find a used one.
http://www.robotroom.com/ReversedLED.html
Making an Amplified Color Sensor from an LED and an Op Amp
Reversed LED Sensor: 1.Basic Circuit
2.Op Amp Schematic
3.Oscilloscope Traces
4.Signal To Noise
5.Op Amp Speed
Making an Amplified Color Sensor from an LED and an Op Amp
One of the first lessons that an electronics student learns is that an LED provides light from current flow. But, did you know that an LED put in backwards provides current flow from light? Yes! It’s true.
Don’t believe me?
A multimeter in voltage measurement mode detects voltage in a discrete LED when held close to a light source.
A multimeter in voltage measurement mode detects voltage in a discrete LED when held close to a light source.
Hook up a high-quality ultra-bright red LED by itself (no battery or other circuitry) to a multimeter in voltage measurement mode. Put the LED against a light source, such as a desk lamp. See the voltage? Now, hide the LED in a dark place. See a decrease in voltage?
An LED (light emitting diode) is a photosensitive semiconductor with a lens. The LED acts as a photodiode.
Photodiodes are used in robots and devices as light sensors. Photodiodes have a spectrum wavelength to which they are most sensitive, usually infrared. But, not surprisingly, a reversed LED is most sensitive to the same color of visible light as it normally emits. For example, if a circuit uses a reversed green LED, the most current will flow from exposure to green light.
Photodiode Amplification
Unfortunately, even under the best conditions, photodiodes (and reversed LEDs) don’t provide a lot of current flow. The output of the photodiode needs to be amplified for the light-detection signal to be useful in most circuits. A photodiode amplified by a built-in transistor is called a phototransistor.
You can connect a standalone photodiode to the input of a standalone transistor. But, it isn’t easy to control the gain of a single-transistor amplifier, and there are issues with signal noise and the amount of input current required. Instead, a better method for amplifying low-power signals in a high-quality repeatable way is an op amp chip (operational amplifier).
Putting this all together - a color sensor can be made from a reversed LED and an op amp chip. In fact, TAOS did just that with their TSLR257 (red), TSLG257 (green), and TSLB257 (blue) sensors.
Example schematic for amplifying a photodiode using an op amp.
Example schematic for amplifying a photodiode using an op amp.
•LED1: Normally an LED has the diode arrow pointed down toward ground because conventional current flows that way. But, this reversed LED points up. The more light that hits it, the more current will flow.
•IC1: The op amp takes the weak signal of the reversed LED, amplifies it, and sends it out the output pin. IC1 must be a ultra-low input current op amp. That means the chip can work with very little input current, which is good because the reversed LED can only produce a little current. This trick won’t work with an old-fashioned op amp, because it requires a lot more input current.
•R1: This is an extremely high-resistance resistor. Although TAOS uses a 320 megohm resistor, the next circuit in this article only requires 30 megohm.
Resistor R1 allows a teeny tiny bit of the op amp output to feed back into the input signal. If R1 didn’t exist, the high-gain op amp would amplify the LED1 signal so much that it would simply max out at 5V all the time. But, by taking a bit of current and feeding it back, R1 reduces the LED signal just enough so that the op amp output voltage is a usable level somewhere between 0V and 5V.
Think of R1 as the volume control. Crank the resistance too high and the output becomes too loud (oversaturated). Set the resistance too low and the output becomes too quiet to be useful.
•C1: Because this circuit deals with extremes (low input signal, high resistance, high gain), it may oscillate (change values back and forth) unintentionally. Therefore, a small amount of capacitance (likely in the picofarad range) can stabilize the signal.
Sadly, the TAOS TSLx257 family of color sensors has been discontinued. It’s too bad because they were a compact and easy solution.
However, this same type of circuit appears in white papers and technical notes for both National Semiconductor’s and Texas Instrument’s op amps. So, you can build a color sensor circuit using their parts.
Although the circuit will be a lot larger than one integrated into a single component, you'll be able to select specific wavelength sensitivity through your choice of LED color. And, you'll be able to determine the desired amount of signal gain through your choice of feedback resistance.
On the next page you'll see the complete schematic and solderless breadboard for the reversed LED color sensor. The remainder of the article is devoted to a series of oscilloscope traces showing the photodiode signal in action. These trace tell the story of why certain parts in the circuit improve the accuracy of the digital output and the signal-to-noise ratio on the input.
