Solar-Power the Circuit Cellar (Free Download)

In the spirit of DIY engineering and solar power innovation, we’re re-releasing Circuit Cellar founder Steve Ciaria’s three-part series, “Solar-Powering the Circuit Cellar.”

An excerpt from the first article in the series appears below. And for a limited time, you can download the entire series for free. Enjoy!

The photos show the roof-mounted solar panels that produce approximately 40% of the total PV power. I know it sounds like a joke that the first PV system consideration is walking around the house and looking for the sun, but you can’t generate much energy if your panels are always shaded. When you live in the middle of the woods, finding the sun is often easier said than done.

Approximately 4,200 W of PV power is generated from 20 roof-mounted SunPower SPR-210 solar panels. The other 6,560 W comes from pole-mounted arrays behind this area.

Approximately 4,200 W of PV power is generated from 20 roof-mounted SunPower SPR-210 solar panels. The other 6,560 W comes from pole-mounted arrays behind this area.

Array orientation determines how much energy you can produce. Solar panels are typically aimed due south at a specific tilt angle that optimizes the incidence angle of the sunlight striking the panel. Maximum energy is produced when this tilt angle is equal to the latitude of the location (reduced by a location correction factor). Typically, the optimal tilt angle during the summer is the latitude minus 15°, and the optimal angle for the winter is the latitude plus 15°. Hartford, CT, is located at 42° latitude and the optimum tilt angle (minus an 8° correction factor) ranges from 19° in the summer (34° – 15°) to 49° in the winter (34° + 15°). The Connecticut rebate program suggests that if a fixed tilt is used, it be set at 35°. Of course, these are computer-generated optimizations that don’t necessarily accommodate real-world conditions. While it requires some nontrivial computer calculations to show authenticity, it is my understanding that as long as the non-optimal differences in azimuth and tilt are less than 20°, the loss in maximum power production is typically only about 5%. It is exactly for that reason that the most cost-effective PV installation is typically a fixed-pitch roof-mounted array.

Team installing solar panels on Steve Ciarcia's roof

Team installing solar panels on Steve Ciarcia’s roof

My system includes both variable and fixed-pitch arrays. The roof-mounted panels are located on the solarium roof and oriented at a fixed pitch of 17.5° facing SSW (see Photo 1). According to Sunlight Solar Energy’s calculations, efficiency is still about 92% of the desired maximum because the 17.5° roof angle actually allows higher efficiency during longer summer hours even though it isn’t the optimum tilt for winter.

Pole-mounted arrays are more efficient than a fixed-pitch roof array by design. My configuration is single-axis adjustable. The pole-mounted arrays are oriented due south and enable seasonal adjustment in the tilt angle to optimize the incidence angle of the sun. For everyone ready to e-mail me asking why I didn’t put in a tracking solar array since this is a pole mount, let me just say that you can also send me financial contributions for doing it via the magazine.—Steve Ciarcia, “Solar-Powering the Circuit Cellar (Part 1: Preparing the Site),” Circuit Cellar 209, 2007.

Check out some of Circuit Cellar’s other solar power-related articles and projects:

Cabinet-Based DIY Electronics Workspace

Micrcontrollers and electrical engineering probably don’t come to mind when you flip through an IKEA product catalog. But when you think about it, IKEA has plenty of easy-to-assemble tables, cabinets, and storage containers that could be handy for outfitting a electronics workspace or “circuit cellar.”

(Source: Patrik Thalin)

(Source: Patrik Thalin)

Sweden-based Patrik Thalin built a workspace within an IKEA Husar cabinet. The setup is compact, orderly, and well-planned. He noted:

It has a pull-out keyboard shelf that I use it as an extension of the workspace when the doors are open. My inspiration came from a friend that had built his lab in a two door closet. The main idea is to have a workspace that can be closed when not used and to be able to resume my work later. I have used this lab for nearly ten years and I am still happy with it!

In the upper part of the cabinet I keep commonly used tools and instruments. On the top shelf are two PSUs, a signal generator, assortment boxes with components, the SMD component kit and shelf trays with cables and small tools. On the lower shelves are things like multimeter, callipers and a power drill. At the bottom is the work space with a soldering station. On the left wall are screwdrivers,wrenches and pliers. To the left are cables hanging on hooks.The thing hanging under the shelf is an old radio scanner. You can also see a small vise hanging on the front of the workspace.

The lower part of the cabinet is for additional storage, he noted.

(Source: Patrik Thalin)

(Source: Patrik Thalin)

The information and images were submitted by Patrik Thalin. For more information about his space and work, visit his blog.

DIY Arduino-Based ECG System

Cornell University students Sean Hubber and Crystal Lu built an Arduino-based electrocardiography (ECG) system that enables them to view a heart’s waveform on a mini TV. The basic idea is straightforward: an Arduino Due converts a heartbeat waveform to an NTSC signal.

Here you can see the system in action. The top line (green) has a 1-s time base. The bottom line (yellow) has a 5-s time base. (Source: Hubber & Lu)

Here you can see the system in action. The top line (green) has a 1-s time base. The bottom line (yellow) has a 5-s
time base. (Source: Hubber & Lu)

In their article, “Hands-On Electrocardiography,” Hubber and Lu write:

We used the Arduino Due to convert the heartbeat waveform to an NTSC signal that could be used by a mini-TV. The Arduino Due continuously sampled the input provided by the voltage limiter at 240 sps. Similar to MATLAB, the vectorized signal was shifted left to make room at the end for the most recent sample. This provided a continuous real-time display of the incoming signal. Each frame outputted to the mini-TV contains two waveforms. One has a 1-s screen width and the other has a 5-s screen width. This enables the user to see a standard version (5 s) and a more zoomed in version (1 s). Each frame also contains an integer representing the program’s elapsed time. This code was produced by Cornell University professor Bruce Land.

As you can see in the nearby block diagram, Hubber and Lu’s ECG system comprises a circuit, an Arduino board, a TV display, MATLAB programming language, and a voltage limiter.

The system's block diagram (Circuit Cellar 289, 2014)

The system’s block diagram (Circuit Cellar 289, 2014)

The system’s main circuit is “separated into several stages to ensure that retrieving the signal would be user-safe and that sufficient amplification could be made to produce a readable ECG signal,” Hubber and Lu noted.

The first stage is the conditioning stage, which ensures user safety through DC isolation by initially connecting the dry electrode signals directly to capacitors and resistors. The capacitors help with DC isolation and provide a DC offset correction while the resistors limit the current passing through. This input-conditioning stage is followed by amplification and filtering that yields an output with a high signal-to-noise ratio (SNR). After the circuit block, the signal is used by MATLAB and voltage limiter blocks. Directly after DC isolation, the signal is sent into a Texas Instruments INA116 differential amplifier and, with a 1-kΩ RG value, an initial gain of 51 is obtained. The INA116 has a low bias current, which permits the high-impedance signal source. The differential amplifier also utilizes a feedback loop, which prevents it from saturating.

Following the differentiation stage, the signal is passed through multiple filters and receives additional amplification. The first is a low-pass filter with an approximately 16-Hz cutoff frequency. This filter is primarily used to eliminate 60-Hz noise. The second filter is a high-pass filter with an approximately 0.5-Hz cutoff frequency. This filter is mostly used to eliminate DC offset. The total amplification at this stage is 10. Since the noise was significantly reduced and the SNR was large, this amplification produced a very strong and clear signal. With these stages done, the signal was then strong enough to be digitally analyzed. The signal could then travel to both the MATLAB and voltage limiter blocks.

Hubber and Lu’s article was published in Circuit Cellar 289, 2014. Get it now!

Arduino-Based Lathe Tachometer

Want an electronic tachometer to display the RPM of a lathe or milling machine? If so, Elektor has the project for you.

The electronics tachometer design features an Arduino micro board and  a 0.96″ OLED display from Adafruit for instantaneous readout. The compact instrument also has a clock displaying the equipment running time.

Navy Engineer’s Innovation Space

When electrical engineer Bill Porter isn’t working on unmanned systems projects for the Navy, he spends a great deal of engineering time at his workspace in Panama City Beach, FL. Bill submitted the interesting images that follow (along with several others) for an interview we plan to run an upcoming issue of Circuit Cellar magazine. Once we saw his workspace images, we knew we had to feature it on our site as soon as possible.

The workspace of a true innovator (Source: Bill Porter)

The workspace of a true innovator (Source: Bill Porter)

Check out Bill working on a project. He told us: “I am a hardware guy. I love to fire up my favorite PCB CAD software just to get an idea out of my head and on the screen.”

Bill is self-proclaimed "hardware guy"

Bill is self-proclaimed “hardware guy” (Source: Bill Porter)

Interesting the sorts of things Bill designs? Check out his wedding-related projects.

Pretty unique proposal, right? (Source: Bill Porter)

Pretty unique proposal, right? (Source: Bill Porter)

This is just one of the many electrical engineering-related items developed for his wedding (Source: Bill Porter)

This is just one of the many electrical engineering-related items developed for his wedding (Source: Bill Porter)

You’ll be able to learn more about his innovations in a future issue of Circuit Cellar magazine.

Share your space! Circuit Cellar is interested in finding as many workspaces as possible and sharing them with the world. Email our editors to submit photos and information about your workspace. Write “workspace” in the subject line of the email, and include info such as where you’re located (city, country), the projects you build in your space, your tech interests, your occupation, and more. If you have an interesting space, we might feature it on CircuitCellar.com!