Archive for category how-to
We’re working on some energy harvesting projects – and we learned about this amazing project – a radio powered only by the sound of the voice of the person talking at the transmit end.
This was able to transmit 150 miles with NO batteries at all. And no ‘super caps’ either. Just the transient power of his voice. Michael Rainey provides a schematic here: Schematic of voice powered transmitter, El Silbo.
The trick for using a speaker as a microphone to absorb sound wave power is to get a good step-up transformer. The speaker has current, but little voltage, even into a high impedance. Of course, you can get more power output using the tin can approach, demonstrated in this video:
This phase controller uses the tried and true back to back SCR technique. It’s and old unit but still in service, partly due to our repairs and system debug. About half the gear in the photo is our test jig. Watch out for ‘flux doubling’ when you turn on/off that big toroid transformer! We kept blowing the 20A breaker until we set up the variac on our bench set up.
We’re using some Arduino boards for a variety of projects – to run the motion stage (25um resolution), to test LED colors, to run an oven for testing temperature compensation electronics. The add on boards (‘shields’ – since that means something else to me, I have trouble with that name) are a big help. We’ve been using SparkFun as our Arduino parts vendor, and we like ‘em.
Recently we designed and built a precision motion stage capable of focus adjustments to about 0.5um. Yes, that is 500nm, or about the wavelength of green light. It’s stable, has smooth travel of a few mm. Based on a flexure design, so there’s no bearings to ‘rumble’ or cause misalignment.
This project shows how we combine off the shelf parts and custom parts to get a job done. Our goal was helping our client specify their unusual custom lens, so that it could be manufactured. Their custom lens had to work with a range of existing medium format photo lenses and with cinematography ‘prime’ lenses. Since the catalog information about these medium format and cinema lenses was not detailed enough for our client’s design needs, we needed to make some measurements.
The common image quality metric is the Modulation Transfer Function, MTF. The MTF function describes the image modulation vs. spatial frequency – perceptually, it’s equivalent to contrast. Good looking images have high contrast in the mid range spatial frequencies. (For more info, check out this excellent tutorial on this topic, Norman Koren tutorial about MTF ).
We used some parts from Thor labs, our PointGrey camera, the excellent ImageJ software, and our own flexure stage design.
We needed an imager with 0.5 micron pixels, so we used a 10X microscope objective in front of the PointGrey camera (which has about 5um pixels) to get the line pair per mm resolution we needed for the tests.
The custom lens design for our client requires an image modulation consistent with the cinema/large format lenses used in the application. The MTF data is infrequently given in these commercial camera lens data sheets, we realized we needed to measure the MTF ourselves. We found an excellent method to calculate MTF from an image of an optical step, which was purposefully slightly misaligned to the imager pixel array. Intuitively, each pixel acts as a pinhole, the array of pixels effectively scans the pinhole, and the resulting data are like scanning the edge of the image bar. The computer program calculates the MTF from the “scanned edge” profile.
We needed an imager with 0.5 micron pixels, so we applied the idea of a scanning micro-densitometer. The micro-densitometer uses microscope optics to magnify the image structure in the film for subsequent analysis. So we reached into our lens bin for a 10X microscope objective.
We found rotating the focus ring on the camera lenses was inadequate for precision focus, and our work was compounded by a lens without a focus ring. The camera this lens is designed for has a translating lens mount, with a bellows for eliminating stray light. Our lens bench does not have the precision required for focus either.
The problem was solved by combining a flexural translation stage with a differential adjusting screw from Thor Labs. This screw advances 250 microns per revolution with the external threads, and the internal differential screw advances 25 microns per revolution. At first use, it was apparent the design was adequate for the task.
We verified the performance of the 10X objective by getting crisp images of a Roncii ruling. Then we measured the on axis MTF of the photographic lenses of interest to learn that part of lens performance.
Our first, hand made, stage was not robust enough for laboratory conditions. We decided to design and build a robust version that interfaced easily to commercial optical bench components. The attached photos show the device almost ready for work.
Here’s a pdf version of this document, which includes Thor Labs part numbers for the lens tube parts needed, MTF-Testing-071510.
Here’s the specs: Voltage noise 2.5nV/√Hz, Gain 1000, bandwidth 0.3Hz to 500kHz. I measure 600nVpp from DC to 1kHz at the output.
Here’s the story: Designing and debugging a high precision A/D stage, you will want to know how quiet the voltage reference really is. When I worked on a 20 bit A/D board, I found this amp a great way to prove that a simple voltage regulator was not good enough as a reference voltage (measured data trumps an any preconceived notions). It was a big help getting the shielding and grounding debugged too!
Since most ‘scopes have about 5mV/Div at their highest gain, this AC-coupled amp allows you to ‘see’ to 5uV/Division. For a 5V full scale A/D that’s 1ppm per division on your ‘scope. Trust me, you’ll see things there. (I read that Pasteur freaked out his dinner hosts, using his microscope to look for germs on his food. He was ‘debugging’ in his day too, with his new favorite toy).
Here’s a pdf of the schematic – it’s based upon the design in the book Low-Noise Electronic System Design, by Motchenbacher and Connelly (a highly recommended text). Since the text came without the amp, I had to make one myself.
I also have a SPICE model for it, using Linear Tech’s LT-SPICE and I’ll send it to you, if ask.
We’re working on a low-noise amplifier product, and to test it we need some attenuation, to generate clean low-level signals. The pdf shows a schematic and describes some test results. It’s a little more tricky than just a couple resistors because with every resistor you get (free!) parasitic capacitance that tends to distort your signals, unless you compensate the network.
Based upon Motchenbacher and Connelly’s excellent book ‘Low Noise Electronic System Design‘. Click on the link for the pdf or on the image for a JPEG version.
Portable electronic instruments. These photos show knobs, nuts, knurled, and know-how (Pete’s). These are working photos of our differential amplifier project. They show how we can get the electrical boards to line up with the mechanical connectors, and controls. And how an extra layer of plexi can be used to add a nice finish, and provide a solution to the incompatible height of the controls (note the nut is recessed by the plexi).
We’ll be teaching a ‘short course’ at the Photonics West 2010 show this January.
Titled ‘Fluorescent Detection: System Design and Tradeoffs’, it’s based on work we did to help develop a hand-held chemical detection instrument for Cogniscent Inc., (homepage for Cogniscent Inc.) who have granted us permission to show off some of the things that went into that product’s design.
We also discuss various design options that were not selected for the Cogniscent system, and what motivated those decisions.
Here’s where you can find more information, at the SPIE website:
For both a clinical test microscope, and a home theater HDTV projection display, the light from the source must be quite uniform.
To test some non-imaging illumination optics, we set up our digital camera, and wrestled with the RAW data files from the camera. Most cameras have some ability to ‘see’ infra-red, so we can also test the pattern from the remote control output, or for other purposes.
Here’s a vendor we recommend, and a photo of some parts they made for us.
When you make one or 10 of something it can be difficult to make it look ‘real’, that is, to make it look finished. Sometimes the Dymo-Marker labels are OK, say in a sci-fi movie, for your Custom Flux-Capacitor. But other times, you want the prototype to look clean.
We have enjoyed using the services of FrontPanelExpress to make some custom front panels for our projects. They provide free software, that’s simple and easy to use, and you upload the files to their on line ordering … and you get great parts back. A variety of anodized aluminum options and thicknesses.
They will engrave text, add paint colors into the text -makes a very nice professional looking prototype or short run of parts.
Just imagine – they can easily make a D-shaped hole for the BNC – so it won’t UNSCREW and FALL OUT !!! That alone is worth the price of admission. I can’t find my D-shaped drill bit …
They can do a lot of things that are a pain to do by hand – countersink holes, nice RS-232 type D-cutouts, square holes, etc. Check out their site for some examples.
We also made a Plexiglass panel – this allows us to compensate for the very annoying differences in height of the switches and knobs – and it allows simple paper graphics to be protected. We also considered making a glowing logo, but have not yet done that.