Apprentices of electronics class

 I kept some time aside to prepare (on Tue) for Xth grade electronics classes at Udavi (on Thu). One of my colleagues asked if I could use an apprentice for that slot. I took up the offer and soon realized that I had picked up one more opportunity to stretch myself - prepare for the Xth class and and find a way to engage Ab. I merged the two for some time working on the demos for the Xth graders e.g. on how AC becomes DC through rectification (half-wave and full wave), then filtering, then the load creating ripples connecting it to regulators. I also was able to use help for checking the connections of counters with seven segment displays. 

When En joined I felt that I needed to create a small independent project that they owned and delivered on. I had received a request for a buzzer circuit that could be used in the school fair that when two wires touched will get triggered and stay on. I thought it would be a good (and challenging) design exercise for them.

 

They attempted to build it on bread board, but had limitations with the relay integrating well into the bread board. They tried to solder a wire on the relay, but got cold solders and the wire would fall off. I let them work through their struggles and once I realized they had understood the components and an intermediate solution even asked them to present it to the 6th graders I work with. In that class, they really seem to notice that they were 'getting it' themselves.

As we were getting towards the end of the year I asked them to direct me step-by-step and offered to do the soldering for them. Once we were done with a basic design of a relay and a switch in series it only buzzed when the wires were touched. I tried to let them explore the puzzle of making it work with a single wire. They couldn't get it and I showed them the positive feedback. As we talked about how it worked Ab came back with, 'oh, that's clever'.

Of course, as all real things in design the circuit did not immediately work and we got down to debugging it by measuring voltages at different parts of the circuit before finally realizing that one of the traces connecting two nodes had got burnt out due to soldering and de-soldering.

It was even more interesting that the circuit worked the first time, but the second time as soon as the switch was turned on, even before wire W1 and W2 were touched to each other the buzzer went off. Can you figure out why? 

We found a work around by connecting the W2 to ground before starting and I realized that I could have asked them to add a diode, but the complexity seemed just right for them and I left it with their understanding of the issue and the work around.

We had a conversation for completion:

How do you feel?
Ab: Happy
En: Like I learnt a lot of things
Me: Complete

What is the first thing that comes to mind about what you learnt in this class?
Ab: Seven segment displays
En: Relay

The second?

Ab: Multi-digit seven segment displays!
En: Piezo buzzer

What would you was missing in the classes?
Sometimes the classes were hard. Would have liked to do a remote controlled car as well. 

Here is them giving a demo of the circuit without realizing that I had turned on the video well in advance ;) -