Secret Knowledge Time Vol II: Servos

For documentation on what the activity was, go here (link not active yet).

This Secret Knowledge Time was all about…what we did last week, but slightly different.  At this point, we hoped to gather everyone who wanted secret knowledge, catch people up on what we had done last week, and to stall for time to figure out how to introduce them to microcontrollers.

This week we made the same 555 circuit, but with a twist.  The output from the 555 was inverted and used to drive a servo (Note: the output had to be inverted because the minimum duty cycle of a 555 is 50%, and the duty cycle we needed was 10%.).  I found a few diagrams online, finagled the resistance values into something we could supply from the stockroom, and the built and tested the circuit.  It worked!

Again, errors are marked with red Xs.

However, our circuit diagram was flawed yet again.  Despite testing the circuit, we had not tested our diagram.  Fritzing drew several lines that we had deleted at some point, but did not technically connect them, because there was no large black dot indicating a connection.  This led to confusion in both myself and the people running the activity, and the people building the circuit.  This time the corrections and things that we had to yell out were:

  1. Corrections to the circuit diagram
  2. What the leads of the servo were (GND, V+, and Signal)
  3. What resistor went where
  4. How the pins on the transistor correlated to the pins on the schematic
  5. How to hook up the potentiometer

With all that resolved, most of the people got the circuit working in about two hours, played with it, and went home.  We got less feedback forms this time, indicating that we needed (and still need) to implement some new kind of feedback.

We had several improvements over the first SK this time.  We had acquired additional 5V power supplies.  We asked Sasha to help us again.  We improved the handout to include background information on what we were doing, and we even had a pretty good slightly better circuit diagram.  The problems we ran into were mostly in explaining the components, in which really is based on the problem of sexy vs. critical.

The sexy vs. critical problem is going to be another theme in TSK.  Some information or skills are sexy, cool, or desirable.  Things like reading brain waves, or blinking LEDs, or making a robot are sexy.  Things like understanding ohms law and how the oscillator in a 555 works are less sexy, but in some cases that knowledge can be critical to doing the cool thing.  The problem is that to get people to show up, you need to promise cool things in a short amount of time, but to achieve that, people will need to know a few critical and unsexy things.  This turns into a chicken and egg problem.

Our solution is just to throw the critical knowledge at them as they do cool stuff.  Sometimes this comes across as being unprepared, but it is almost easier to just do it on the fly as opposed to spending hours typing up detailed explanations of every component.  It also limits how “theory” we can be.  We do not want to be “too damn theory”, which is easy to have happen in a writeup that we are trying to make into a complete, definitive document on a part or subject.  It’s hard to tell where to stop; my best estimate is that a page or half a page is probably as much as anyone needs to know, and that is something that might be handy to have as a reference for TSK.

Overall, TSK Vol II: Servos was a success.  The feedback was mostly the same, but we did have a big question hanging over our heads at the end.  People kept asking:

What’s next?

We thought that was a pretty good question ourselves.

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