We have designed and prototyped a low-cost electronic device capable of measuring the flow velocity inside 1 mm wide microchannels, taking advantage of the light absorbance produced by some fluids. In addition, we have incorporated a spectrometer module capable of detecting 20 different wavelengths of the fluid sample. We have also designed a prototype suction pump that moves the liquid at a constant pressure inside the microchannel, so that it passes through the optoelectronic system and thus facilitate rheology measurements of different fluids, especially those of biological importance such as blood.