Sunday, 4 June 2017

Raspberry Pi User Group Meeting, May 27, 2017

Next Meeting:    June 17, 2017, 10am - 2pm @ New Glasgow Library
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Unfortunately our date had to be changed from our regular Sunday to a Saturday due to the library closing on Sundays halfway through May to the beginning of September. We did have the new date posted on our Kijiji ad but the message did not get out to some people - sorry about that.

There was some time at the beginning of the meeting where I was by myself. I took the time to work on my robot. Connecting the photocells was the first job. I had one photocell connected more or less the way I wanted by the time the first attendee arrived.

Here is the robot with just the photocell (light) sensors and one solderless breadboard, and wheels with geared motors. The screws for the third wheel (a caster wheel) can be seen in three places. To start with, I originally used a screw that was too long for the job. Grounding it down so it would not interfere with anything that might be placed on that section of the robot was too much trouble. Although I left the one ground down screw in place, I went and bought the correct length screws for the rest of the caster wheel mounting holes.

Here are is the robot with LED's connected so that they light up according to which sensor has the most light shone upon it. The LED's are on the far side of the board behind the light sensors.

Our attendee had some modules he wants to use to construct his model train environment. We started off with a forward-reverse relay module purchased from eBay. These modules were from China but had some decent documentation in English. Once we started to work with them, we figured it out. We also found the eBay listing for the same module and watched the video which was close-captioned in English. Watching it in action on the video helped.

One interesting thing we found was that the model train power supply was not not appropriate to run the relay modules. One of them just would not power up. Luckily, we had an Arduino board from which we used the power supply. So, if you are into model trains or interested in getting started with model trains, make sure you have at least one good power supply to test your equipment.

Here is the link to the module:

In the case of testing the relay module, we did not provide a load to switch on so we only had to worry about the current and voltage necessary to run the module electronics used to determine the timing for the forward-reverse cycles. We did not have to worry about the power supply for a motor or how to hook one up. We could hear the relay switch when it powered to indicate it was working.

When borrowing the power supply built into any board, you should have a quick look to see what the power supply circuit can handle. You can do this for Arduino by going to the Arduino website and looking for the relevant board. Look for the hardware schematic. For an Arduino from 2009, the voltage regulator is an MC33269. One of the key properteis to look at when reading the data sheet is the maximum current supplied by the particular device. In the case of the Arduino board, you should also check for Arduino documentation to see if there is anything specific done to the voltage regulator that allows for less or more current than normally supplied by the voltage regulator. Do a web search on the part or go directly to the manufacturer's website to find their data sheet. There are also some sites that provide data sheets from most manufacturers.

We had another module to search for: a servo motor shield. This was easy as it gave the manufacturer on the Arduino shield, what is was, I cannot recall. Do a websearch on "Arduino motor shield" and you will come up with a number of results that will likely serve your purpose. If the websearch provides you with an acceptable result, you should be able to find a relevant tutorial.

Come see us at the library Saturday, June 17, 2017 to see what new things we are using and troubleshooting. The robot should be able to follow light by then! If you look closely, you can see that there is actually no RPi on the robot yet! Give it time.

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