Dermatoscope plays an important role in the field of dermatology. It enlarges the images of the skin disease regions so that the dermatologists can examine them which otherwise cannot be seen by naked eyes. Currently in Vietnam more and more young people suffer from skin diseases such as acne, melasma, folliculitis, blackhead, dry and oily skins. Devices on the market are quite expensive and not always accessible to common users. Images qualities from smartphones are not clinically appropriate due to the reflected light glare. To avoid those issues, we developed here a low-cost device as a clip-on to a smartphone. This combination constitutes a dermatoscope that provides enlarged and clear images of diverse skin diseases. It would eventually be incorporated in an Internet of Things (IoT) system to transfer wirelessly those images to dermatologists for care from distance. The developed device consists of an ATtiny13 microcontroller along with an Arduino UNO module to generate a Pulse Width Modulation (PWM), an LED system whose light intensities are adjustable by the PWM, a circular polarizing lens to eliminate the glare, a microelectronic system and a firmware to control the device functioning. The clinical trials on patients were evaluated by dermatologists. Their positive assessments and good technical performance proved that the device is a clinically valuable tool. Further, with its cost effectiveness and simple design within reach of most low-and-middle income countries laboratories, this dermatoscope can be manufactured by local machine shops and is commercially viable for entrepreneurial people.