The development of a three-legged miniature robot, such as the NanoWalker, capable of taking steps in the micrometer and sub-micrometer range and equipped with instruments such as scanning, tunneling microsope (STM) tip, requires an adequate positioning system. In order to make use of these instruments, positioning the robot becomes one of the most critical issues. For atomic scale operations within a relatively large workspace, no traditional positioning systems were adequate for this type of robotic environment. The proposed atomic scale positioning system relies on three positioning levels where at each level, the resolution improves from 10 micrometers down to a few picometers while the circular positioning area decreases from 0,5 meter down to 200 nanometers in diameter. While the last two levels are STM- based positioning techniques, the first level with the largest positioning area is based on optical techniques. The paper describes the final set-up for implementing the first positioning level that incorporates a lateral effect photodiode to make measurements of the robot's position by detecting infrared signals emitted by the robot. Using a lens to project the robot's workspace onto the photodiode we are able to achieve of a resolution of a few micrometers in the central region of a typical 0.5-meter workspace. Due mainly to loss of signal at the edges of the workspace,the resolution of the system decreases as we near the edges.