Data Logger

On 24th October 1995, a Total Solar Eclipse (TSE) was visible from the northern part of India. Khagol Mandal, the biggest amateur organisation in India, experienced the eclipse from Hamirpur in Uttarpradesh where totality lasted for about 1 minute. Various groups in Khagol Mandal had conducted different experiments like recording light intensity, temperature change, humidity change, wind direction, contact timings, flash spectrum of the sun, biological experiments, etc. I was in the 'contact timings' group. As the totality approached, the excitement in the air started growing. My hands started shivering because of the thought that I was going to experience something very extraordinary, something that was a life time achievement. I was unable to start the stop watch at the proper time. I started it about 10 seconds early. My brain told my hands to reset it and start it again, but my hands refused to move. As the totality got under way everyone was off the ground. I discovered myself on my feet and clapping spontaneously. The experiment was left behind. Very few were able to concentrate on their experiments because watching the eclipse was more important. Those who did concentrate, repented afterwards for the missed opportunity. After the eclipse, it was decided to automatize the experiments so that humans won't be held up in performing them.

On 11th August 1999 we went to Bhuj in Gujarat for watching the total solar eclipse. Our group had automatized two of the experiments, light intensity measurement and temperature measurement. We used the 8085 microprocessor development system (MDS) as the processing unit. An 8 channel ADC card was interfaced to the on board 8155 port, though only 2 channels were actually used. We had to build some more circuits like a digital clock and a signal conditioning circuit for the light sensor.

For the signal conditioning circuit, we used the circuit developed by my friend Shriram and me at the Diploma project. It was the LDR characteristic Linearizing circuit. This circuit gave linear output voltage with respect to the input light intensity falling on the LDR, the L-R characteristics of the LDR being nonlinear.

A highly accurate hardware digital clock of 1 Hz was constructed to get an accurate reference time. The hardware clock would interrupt the CPU every second and then a subroutine would read in the temperature and light intensity values and log it.