Calculating Densitometer

The "Calculating Densitometer" is actually the same densitometer I had built using the Basic Stamp II, a pair of Texas Advanced Optical TSL230 programmable light-to-frequency converters and a constant current source for the LED.  In this circuit, however, the Stamp is replaced with a PIC16F84 microprocessor.  The 16F84 is connected to a host computer via a Maxim 232 serial interface chip to create the RS232 levels needed to talk with the computer's serial port.

As before, a Maxim 7219 LED driver is used for a 3 digit display.

What isn't shown above (for the sake of simplicity) are the pullup resistors, the MAX232 chip or the power supply.