I want to use the Velleman K8055 for data collection and also for remote control, so I started testing the analog inputs for sensor.
The first pair of sensor (will multiplex the inputs for others) is to get light conditions, will put a south faced solar power meter and a light above intensity meter. The relation between both during the day will, I hope, give me rough idea of the sky conditions.
For the light above intensity meter, the idea is to have a small tube pointing up with an LDR in the lower part. Since the K8055 analog inputs basically measure voltage I used an voltage divider, series of the LDR and a fixed resistor. For the South faced solar power meter nothing simpler than a small solar cell, I used two to compensate losses in the cable (will be a long cable run and the cells output very low power). Across the cells there will be a resistor for direct power measurement.
For fun, I run some simple math on the power from the solar cells and if scaled I would got 100W by each square meter (had no ruler by hand to measure the little cells so it was a ball part guess), the panels represent 0.00024 m2 and considering a 500W of total solar power during daylight hours that would give me a 20% in efficiency... a plausible figure considering the inaccurate data.....
Other sensors will follow, maybe next will be temperature.