Humboldt Microcontrollers Group July 24 2014 Meeting Notes

Redwood Curtain Brewing Company

This is a summary of the July 24 meeting of the Humboldt Microcontrollers Group at The Link in Arcata, California, behind the Redwood Curtain. Speaking of the curtain, maybe the Humboldt Microcontrollers Group should schedule an upcoming meeting to be held at Redwood Curtain Brewing Company. Microcontrollers can be used in brewing...

One of the reasons for this blog and for the formation of the Humboldt Microcontrollers Group is the redwood curtain, which is both an actual and perceived barrier between Humboldt County and the rest of the world. In many ways, that curtain is a much appreciated and highly beneficial barrier, preserving natural beauty, creating a slower pace of life, and leading to a better balance between work and non-work activities. But in other ways, that barrier brings economic challenges and limits both the job opportunities for people and growth opportunities for

The curtain between Humboldt and the rest of the world

companies. One way to reduce the redwood curtain barrier for people and companies in this region who work with microcontrollers (MCUs) is to connect, strengthen, and promote the Humboldt microcontroller community. This blog and the Humboldt Microcontrollers Group are both working to connect, strengthen and promote that community.

So, the main topic of the July 24 meeting of the MCU group was the #8 Jeremy Blum Arduino video tutorial (see also my previous post about that tutorial). The focus of the #8 tutorial is SPI (Serial Peripheral Interface), and Jeremy uses an AD5204 digital potentiometer to demonstrate the use of SPI. Ed Smith used a different digital potentiometer than the hard-to-find AD5204 when he did the #8 tutorial exercise, so the sketch Jeremy wrote in the tutorial doesnt work correctly because of the differences in the two potentiometers. Well have to figure out an appropriate alternative potentiometer and accompanying code for other Humboldt people who want to do the #8 tutorial exercise. One more item to add to the list of things-to-do regarding developing a set of effective learning tools for people in this region interested in MCUs.

No one at the meeting had actually worked through the exercise in tonights video. Since none of the people at the meeting tonight had done the exercise, we didnt spend too much time talking about either the technology of a digipot or about interesting or unique aspects of SPI. Maybe at a future meeting? My plan is to talk with Ed, Nick and anyone else interested to agree on a good alternative digital potentiometer and to modify or rewrite the Arduino sketch to work with the digipot we choose.

In addition to the #8 tutorial, the following topics were discussed at the meeting:

• Somewhat related to the #8 tutorial, Bob asked about using a digital potentiometer (or other components / circuitry) to match color and intensity in a set of three LEDs that are simultaneously given the same input signal but seem to generate different colors. The LEDs are Cree PLCC4 (plastic leaded chip carrier) 3-in-1 SMD LEDs. Based on the little bit we could figure out during tonights meeting about how the LEDs are powered and controlled, Nick suggested the first step should be to put an oscilloscope on the lines going to each 3-in-1 LED to confirm theyre all seeing the same signal. Nick also said its likely the LEDs are adjusted by PWM (pulse width modulation) rather than by varying the power to them, so the digipot would probably not be a possible way to adjust the colors. If all three are seeing the same signal, it would appear unit variability in the LED color output may be the issue. The spec for the LEDs says "Tolerance of measurement of dominant wavelength is ±1 nm" so that spec appears pretty tight. I need to research the issue of bin codes and figure out how to determine if the 3-in-1 LEDs we purchased for this order have green and blue LEDs all from the same bin code. According to the datasheet, the red LEDs only have one bin code (which identifies the wavelength range for that LED), but the blue and green LEDs for this particular component each have seven bin codes. So if some blues were at the bottom of the wavelength range and others were at the top, that might result in a noticeable color difference even with the same applied PWM signal. Of course, keep in mind that my knowledge about PWM signals applied to 3-in-1 LEDs, or other types of RGB LEDs, or even single color LEDs is extremely limited. Researching this will definitely be a learning exercise.



HLH frame

• An update about the Humboldt Laser Harp (HLH) project was given to the group by Nick and Ed. Nick has the frame of the HLH just about completed. In the upper picture on the right you can see the laser harp frame. If you look near the top of the lower picture on the right, a bit of a laser beam is visible -- first sighting of the infamous HLH laser beams. One outcome of tonights meeting is that Gordon will be working with Nick to design and build a base for the harp. Gordon also had an interesting suggestion for laser beam presence enhancement in brightly lighted areas. He suggested shooting the laser through a diffusing or side-emitting light pipe for part of the distance from the laser to the light sensor.
• From a HLH programming standpoint, Ed has been crafting the code that will convince the Humboldt heavenly harp to generate many marvelous melodies. In version 1.0 of the HLH, the goal is to have a demonstration device that produces simple tunes and has a reasonable degree of casual interactivity with curious members of the general public. Future versions are envisioned that incorporate music-correlated lighting effects and more musical instrument capabilities, e.g. lots of simultaneous notes, note strength and fade effects, simulation of different musical instruments, allowing notes from several octaves, different type of controls for the musicians playing the HLH, etc. As with many other maker

  

  HLH laser beam

  topics, there are lots of people who have specialized in the field of DIY electronic music, and much of what well be doing in the early days of the Humboldt Electronic Light Orchestra will be research on whats already been done, connecting with people in the DIY electronic music field who are willing to share their knowledge or who are interested in what were doing, and starting to develop new (as far as we can tell) electronic music ideas of our own.
• The plan is for Nick and Ed to get together this weekend, connect the hardware with the software, flip the switch, and see what happens on the HLH. Stay tuned for updates and videos...
• We discussed the upcoming August 2 maker fair in Eureka, which has been organized by Origin Design Lab. Nick and Gordon will figure out if Gordon has any maker projects that would be good to have at the Humboldt Makers table. Shawn Dean from InPrinting will be at the table doing 3D printing demonstrations. It would be great if other Humboldt Makers can spend an hour or a couple hours at the maker fair, which sounds like it will primarily be a craft fair aimed at being a selling opportunity for local craftspeople. Even if you cant be at the Humboldt Makers table, if you have an item that will be interesting to the general public, please contact Nick Appelmans or me (my email is arcatabob (at) gmail {dott} com).
• Justin suggested the Humboldt Makers might consider doing a minor repair on the 3D printer that InPrinting nearly finished building some months ago, then figure out what else needs to be done to get the unit printing. We can discuss that at the next meeting as either an activity to spend a couple Thursday meetings on, or a project that one or several people would work on as time becomes available.

Hope to see lots of people at the next Humboldt Microcontrollers Group meeting, which will be on August 7.

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