I managed to cram in integer adder AND three double digit hex displays by using ANALOG circuitry for addition!
This circuit converts two 8-bit registers to analog voltage in the range of [0..16) volts using four 4-bit DACs, sums the voltages and converts result back to binary representation using 8-bit ADC for display.
8-bit ADC is implemented with two 4-bit ADCs paired through the (topmost) operational amplifier and DAC.
Overflow of addition is detected by the 3rd (bottommost) operational amplifier. Overflow is displayed by blinking the dot in the output display on the right. Note that unlike binary adder, analog result will not wrap-around in the case of overflow. Instead you will see hexadecimal FF value with a blinking dot.
USAGE: You can enter pair of binary values on the left and result of addition will appear on the hex display in the bottom right corner. In case of the 8-bit overflow the rightmost display with have blinking dot.
NOTE: Such analog adder would be impractical in the real-life due to noise, high-cost and latency of DAC/ADC, however it can be still interesting as a concept.
