This is a very simple analoque to digital converter circuit based on 8-bit analog-to-digital converter ADC0808. Typically analogue-to-digital converter (A/D Converter / ADC) requires interfacing through a microprocessor to convert analogue information into digital format. This needs extra hardware and appropriate software, resulting in more complexity and hence the total amount of cost.
Here the Arduino UNO schematic diagram (click to enlarge): About Arduino UNO: The Arduino Uno is really a microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 may be employed as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, along with a reset button. It contains every little thing needed to support the [...]
The following diagram is the Clock Generator circuit diagram which build based on NAND Gate logic IC. You may use IC 7400 or 4011 for this circuit. The 7400 is a TTL type, while 4011 is CMOS type. IC 4011 is cheaper than 7400 but the 7400 is faster than 4011. Circuit Notes: Excellent clock generator to drive 4017 type cmos circuits. R1 = 10K to 10M, C1 = 100pF [...]