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July 31, 2014

Electronics: Bigshot camera lessons

The gearbox on the bigshots gives an opportunity to dwell into the energy generation in the camera using a manual crank. I had already demonstrated that only at reasonable rotation of the handcrank the battery charges.

I wanted to give children something tangible to measure so I can connect it back to math (especially decimals as I am in the process of introducing these). For the measurements I needed to introduce the multi-meter. I started with the most exciting feature of the multi-meter, the continuity test and though I had not intended for it to become an entire class the children did not tire of getting materials that they thought would conduct or not conduct electricity. The most interesting choice of elements being magnets.

I next introduced DC voltages. I still find it amazing how much of electronics terminology is commonplace with children. They knew it was called Direct Current, but didn't know why. I called it a battery voltage. We measured various batteries and learnt how to read the voltage rating on the batteries.

With a bit of difficulty with water analogy I have started to use the body and flow of electricity to the flow of blood in the body and the battery as the heart that pumps the blood through the body. The voltage in this analogy is the pressure with which the heart pumps. Children relate it to when they are engaged in a physical activity and their heart pumps harder/faster.

We then measured the voltage of the rechargeable battery of the bigshot camera. We found it to be 4.1 V. The children summarized that what was charging this battery had to be greater than 4.1 V. They were quite surprised when they disconnected the battery measured the output of the PCB was 0 V. I then reminded them that that hand crank was disengaged. On rotating the hand crank they did get a voltage around 5 V (not loaded with battery). 

The Bigshot learning material talked about how the AC from the dynamo gets converted to DC for the battery. I felt that could be something fun to measure and realize the difference between DC and AC. I let the children measure with multi-meter still set in the DC mode for the children to see that an AC gives zero DC. We bypassed the PCB and directly measured the output of the dynamo. It was I who was in for a surprise, the meter read 9 V during one of the turns. I realized that it was only a small DC motor giving un-regulated DC voltage that was being regulated for the battery by the PCB. The pic below follows the link to the images:

I noticed that children are really struggling with indoor images and if you are absolutely still when taking the shot, you can get a few decent shots. Something I need to train the kids in.

A few children had done the demonstration for the class and I thought this was something they could all measure. I brought in few cameras assembled by other grades and we disassembled these cameras. The next day I split the class in groups of two and gave the choice to do the measurement or to assemble the camera. Its little surprise the children wanted to assemble the camera. This was the smallest (2 in a group) and youngest group I had given the task to and they went about it quite nicely. I also found the first broken part (a tooth of gear C) and  the first missing part (an axle) after all the assembling and disassembling by the children.

One interesting mixup was when one group accidentally connected the battery to the dynamo. The hand crank started to rotate and the kids were spooked. Well, it did confirm that we were working with a DC motor as a generator. Here are some images from the assembly:

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