First gather the following items you will need to build the LED LYT METER:
PIC Microcontroller (I used the 18F4550)
LCD Screen (2x20 or 2x16)
Now you should be able to follow the schematic to assemble the circuit on a breadboard or any other way that you like to put your circuits together. This one is fairly easy and has minimal parts. I did attach two different schematics, the one has the light measuring LED connected to two different microcontroller pins and the other one has this LED with the cathode (or negative end) connected to a microcontroller pin and the anode (or positive end) of the LED connected to ground. This seems backwards but, remeber, we are not using the LED to produce light, but to measure it instead. That is why it is connected in this way. In my pictures you will see that the LED is connected to two pins of the microcontroller. This is because I wanted to be able to use the LED to produce light too, in order to check to make sure it works when the program is started.
If you do choose to connect the LED to 2 pins of the microcontroller you will need to keep this in mind for it to work. I could not find this documented anywhere so it took a little experimentation to get it to work. In order to be able to light up the LED both microcontroller pins will need to be set as OUTPUTS. Then, to make the LED shine, you set the anode (or positive end) of the LED high so that current flows through the LED to produce light. At first I thought that I would need to set the cathode (or negative end) of the LED as an INPUT but this did not work.
Now that you have the componenets, put them together on the breadboard by following the schematic you want to follow. When assembled, it should look somewhat similar to the pictures below. I am using a 5 Volt Regulator to supply 5 volts to power the circuit. I use a 'wall wart' that supplies about 9 volts to the regulator.
The LCD screen that I am using is a Newhaven Display NHD‐C0220AZ‐FSW‐FTW COG (Chip‐on‐Glass) Liquid Crystal Display Module. I used to use the HD44780 LCD displays that many other people use. You can definiately use the HD44780 displays without any problem and there is a lot more source code out there to make them run. The Newhaven display had no source code but sitting down with the data sheet and using the HD44780 source code, I came up with the code to make it work perfectly. I like the display for a few reason. The contrast is very easy to set and so far I have not had to change it at all during the different seasons, it always remains clear and very easy to read. It also has a smaller footprint and was exactly what I needed for a huge project that I am working on where available space is at a premium. It is smaller and than the HD44780 displays and still displays 20 characters on each of the two lines. Finally, it is less expensive than the HD44780 displays as well. I picked a couple of these up from Digikey and at only a price of $10.25 each. Check them out here: Newhaven LCD Display at Digikey
. Keep in mind that this display requires from 3.3 to 5.5 volts so keep that in mind when choosing your power source. The source code that is supplied should also run the HD44780 displays without any problems.
This is just the way that I have it set up. You can place the components to diffent pins of your microcontroller. Just keep in mind which pins of the microcontroller you connect to the positive and negative end of the light sensing LED. You can also wire up your LCD screen to operate in 4-bit mode instead of 8-bit mode as illustrated. That would require four less connections in the circuit but makes your programming just slightly more complicated.
On to next steps...Writing the Program.