The phenol red is commonly used in cell culture medium as visual pH indicator by changing its color from darker red color to the orange-yellowish color as the pH is changing from neutral to acidic level. The color change of phenol red is hardly to be determined by using naked eyes that will be interpreted differently by different person. Thus, this study is executed to develop a specialized colorimeter for phenol red pH measurement by using Raspberry Pi as a microcontroller unit, green LED as a light source and photodiode in tandem with capacitor as a light sensor. The Raspberry Pi calculated the capacitor charging time which is in relative to the amount of light sensed by the photodiode. Based on the results, the capacitor charging time can be related to the pH value by using non-linear relationship with high accuracy of R2 = 0.8946 and RMSE = 0.4447. This study successfully introduced the development of low-cost system for phenol red pH measurement by applying the capacitor charging time which is in correspond with the absorbance value.