I finally received the PCB for this design. And in general it turned out okay. There were a couple of shortcoming in my design that will force me to to re-spin the PCB, so it’ll be a while before I can finish everything up. But having the PCB gives me the ability to debug my firmware and test the overall concept for this solar panel tracker.
Last week I discussed my latest project, an accelerometer based dual axis solar tracker (that blog is here). When starting a project its easy to get lost in the details. For example, this project has a whole host of possible control functions and interfaces. I’ve always found it useful to start my work on the schematic and hardware. So that’s what I did.
Since this is an R&D project I decided to use some components I haven’t used before. This design will control a 24VDC brushed motor, and a 12VDC brushed motor. I’m going to use two St Microelectronics PN: VNH3SP30-E. They’re rated for 40V and 30A (although there’s no way they can handle 30A without melting off the PCB). One feature I like about these controllers is that they only need a single PWM channel for proportional control. Two other digital channels are used to provide direction. Here’s a section of the schematic that shows the connections between a PIC16F1789 and two of the motor controllers (click the image for a better view).
In the end, this control system will be used to control our dual axis controller that uses a worm gear for horizontal movement, and a linear actuator for vertical movement. Here’s a photo of the assembly in front of the old college text books we could never bring ourselves to throw away. Both the worm gear and linear actual came with feedback. The worm gear was very expensive and has an encoder on the motor. the linear actuator was pretty cheap and came with a potentiometer that failed in about a month. That was one catalyst for attempting that has the position feedback on the control board via an accelerometer.
The circuit board ended up being about 2.5” x 3.5”. Here’s what the top copper layer looks like. The 6 dots on the upper and lower right-hand side of the board are for mounting automotive style blade fuses.
Here is the column from my bill-of-materials.
There are a couple of interesting findings. First, I have an 8MHz oscillator on the design that has the smallest range of operation (-20C to 70C). I’m actually going to use the internal oscillator available in the microcontroller, and I don’t see clock timing to be an incredibly important issue in this design. I added the oscillator part to the schematic as kind of a back-up plan but don’t plan on using it. So I’ll ignore that problem for now.
The next lowest temp. range part is the PDV-P7002, a photocell I will be using to detect daylight. For a part like this, whose resistance changes with light, I would guess that it goes “out-of-specification” outside of its operating range. I doubt it quits working. I’ll have to research that some more, but since I’m using the photocell as a yes/no type input I can accommodate a wide resistance variance.
That leaves me with some ceramic caps that don’t meet my operating temperature range, and I can certainly select a similar part with an extended temperature range, so I’m probably good there.
I guess there was one other issue. The small metal buttons I have on this design (E-Switch parts) had no temperature rating. I thought that was interesting. These are not the kind of buttons you would use in an outdoor design, but no temperature rating?
And now for a sanity check. Am I really going to run this design between –40C and 85C. Nope. This is R&D, it’ll spend its life in my office. If this were a consulting contract we would design for this temperature but suggest our clients place test fixtures in the intended environment to collect operating data and/or make use of a temperature chamber for extended temperature testing.
That’s as far as I was able to get this week. I’ll try to take some time over Christmas break to order the circuit board. I need to panelize it with some other designs so it doesn’t cost an arm and a leg. Hopefully I can begin writing code in January.
A month ago I talked about our next solar demo project. After a month’s reflection, I’ve decide that one is not grandiose enough, so onto the next one. That’s right a solar powered airplane, where there is no margin for error. Just today the plane flew across the Mediterranean Sea from Spain to Morocco. One beguiling aspect of the trip is that it took off in the dark and will land in the dark. That’s right, a purely solar plane is running on battery power! I am not sure if the plane is like a glider and can fly without power, but flying a solar plane in the dark seems more dangerous than flying a fuel-powered plane in the dark. It is not readily apparent from the picture below, but the wingspan on this thing is huge. Check out some more pictures of it here to get a sense of scale.
The designers are gunning for an around-the-world trip in 2014 with a new and improved plane. They started work on this in 2003. I think if we start working right now, we should be able to beat them to the punch by a couple of months. We just need to learn: aeronautical engineering, piloting, aerial navigation, composite manufacturing, and advanced battery technology. On second thought, maybe we can’t get it done that quick.
I have finally started on coding for the solar tracker. As discussed previously, I am venturing out and using a new-to-me processor, the Propeller from Parallax. I am using the Propeller Proto Board for the prototyping. I am using the Prop Plug to communicate with View Port. These last two components provide an ICD-like environment for me to develop the application in. So far I have only scratched the surface with the code – I have basic flashing LED code working. In addition, I’ve run a couple of the View Port sample code applications. Next up: interfacing with two Synaptrons to drive the solar tracker hardware.
So far I am running into the typical issues with using a new micro: figuring out the architecture; determining the way to configure it; and most-importantly – figuring out how to navigate the documentation and web-site to find the information that I need. At the beginning of a design, this last point often becomes the largest hurdle. People, and especially engineers, extra-especially me, are creatures of habit and once we learn a way to do something, it becomes a bit hard to learn a new way to do thing. Related to this point, the biggest issue I am having is learning a new language: Spin. I know what I want to do, it’s learning the syntax that is causing some problems.
None of these issues are deal-killers – they are just typical issues when learning a new microcontroller. As this project is an internal project for our demo, it is necessarily has a lower priority than some other projects, so the progress is slower than normal. However, it is good to get going on the next step for the solar tracker. More details to follow.
Yesterday we sat down and came up with the initial ideas to upgrade the original Solutions Cubed Solar Tracker. Below is the initial block diagram for the new design. This is the rough pass for what the new tracker will be able to accomplish. Basically, we will use the same 2-axis mechanical system with one full-size consumer solar panel on it. We will be able to then roughly follow the sun based on date and time along with the known installation latitude and longitude. From there, we will use a light sensor to fine tune the panel positioning. This is essentially an extension of what we have already done – the big addition will be the battery charging circuit.
While a typical battery charger is fairly straight-forward (we’ve done a few in the past for clients), a charger for a solar panel throws in a few more wrinkles. Specifically, you want to make sure that all of the power from the panel makes it to the battery. So you can’t simply step down the 35Vdc to a charging voltage of +14Vdc, as the power in the headroom is lost to the gods. An actual step-down transformer is necessary – basically we need to make a switching power supply. Cool.
To control all of this we are going to dive into a Propeller from Parallax. We have not used one before, but it looks real interesting. While it lacks a bunch of on-board peripherals, the eight, independent processors will make splitting the work between engineers pretty easy. More updates in the months to come.
We are working on upgrading our solar tracker demonstration project. After that is done, we need to come up with another demonstration project to show off our capabilities. I think I would like to do something like this. That’s right, I think the next logical step for us is to come up with a solar-powered yacht capable of circumnavigating the world’s oceans on sun power alone. We just need to get up to speed on: boat-building, seamanship, navigation, and anti-piracy measures, to name a few. We probably need to move our company from a land-locked location to something on the ocean – probably Tahiti. . . . . OK, maybe that is tearing off too big a chunk for our next project.
But, I really like this accomplishment. Basically, in the name of science and adventure, a Swiss watch company funded this project, which is a 100 foot long, solar-powered, catamaran. It has spent the last two years plying the worlds oceans and will return to it home port of Monaco (of course!) tomorrow. Check out the full website for more pictures, blogs, and details. I’m off to find my admirals hat.
A while back, we were looking for a way of of demonstrating the capabilities of our new line of Synaptron motor controllers, and came up with the idea of building a scaled version of a solar tracker. The two motors controlling azimuth and elevation would be controlled by a pair of Synaptron Micros.
After a bit of research, we decided to use a small slewing drive from Kinematics for rotation and a linear actuator from Firgelli Automation to adjust the tilt of the panels. Slewing drives, and more specifically, slewing bearings are really interesting, as they are able to withstand large loads in both a radial and axial direction. Much larger versions are used on cranes and excavators.
Next, we used Google SketchUp to come up with a basic drawing of the head unit. Here’s a pic of the original design, sans the linear actuator.
The bottom unit is the slewing drive and is able to turn the entire mechanism, as well as stand up to heavy winds and torque loads.
The linear actuator (not shown) will connect at the end of the two arms and be able to adjust the top mounting bracket between 0 and 90 degrees.
Of course then we had to actually build it… More on that later.
It is a first pass demo to get our feet wet in this area. We needed to hone-in our mechanical design abilities (we will have a few blog posts on that coming up) and I needed to use with the Synaptron Micro in a full-sized demo. I was able to get the previous rat’s nest prototype into an enclosure with a rudimentary user interface. There were some last minute snafus – there always are – made the more nerve-wracking because of the deadline pressure. However, we now have a functioning demo, that expo guests can “drive”.
For the demo, you can drive the rotation and the lift of the solar panels in either analog mode (controlled directly with the Synaptron micros) or in serial mode (communication coming from an Arduino Uno). The user is able to use the analog mode with the two silver-dialed potentiometers shown on the box. For serial mode, the keypad is used. The LCD and and LED combinations show the user what mode and what condition the solar panel is in. All in all a pretty straight-forward approach to show-casing the Synaptron Micro’s capabilities.
So why is the demo “kinda” done? As mentioned previously, this was just to get our feet wet. Now that we see it can be done, we want to kick the demo up a notch. Already we know that we want:
- – A custom PCB
- – A better case to display the Synaptron Micros while in operation
- – An integrated power supply
- – Better connections to the two motors
- – Actual solar tracking (by date, location, and sensors)
- – Absolute position tracking for the rotation, not just relative
- – A bigger/better display to show off what is actually happening
- – Professional looking graphics
We will also get some good feedback from the attendees of the the expo, so we should be able to add to the starter list. Keep an eye out for more changes down the road. See you at the expo.