Transmissometry Extended

Note: This project was originally hosted at, but I realized that a fragrance website isn’t really the best place for heavy duty science info, so I moved the transmissometry discussion, source code, and schematics here.

Below is the original post:

Open source hardware saved Campfire #1

I know there are case studies of Open Source Software helping businesses with their day-to-day tasks, but how many case studies are there of Open Source Hardware helping a business solve problems?

Here is my example of how the Open Source Hardware community saved the launch of my company’s first product.

I’ve also included all the theory, technical schematics, and details towards the end.

Here is the video we did for Pumping Station: One and Element 14:

Transmissometer from Pumping Station: One on Vimeo.

How did I get here:

My idea for a campfire scented cologne won the business plan competition at barcamp Chicago 2010, and on May 10, 2011, nearly a year later, I’m ready to launch my product-RuggedScents’ Campfire. Unfortunately, less than four weeks to launch, I discovered a major process flaw: gigantic inconsistencies between the longevity of the fragrance’s smell on the user’s skin from batch to batch-some batches lasted three to four hours, some barely made it past 30 minutes!

<pictures, schematics, and video after the jump> Read the rest of this entry »


Transmissometry: lasers and concentration

I’m starting up a company that makes a campfire scented cologne (I’m actually producing the smoke part of the fragrance myself).  I recently ran into a problem that only open source hardware could solve: figuring out concentration using just how much light my samples absorb.

Here is a blog post with details, schematics, photos, and source code.

Here is a video we shot (with the support of Element 14) to show how the device works:

Transmissometer from Pumping Station: One on Vimeo.


1 year STM project anniversary

It’s now been a year since I first decided to start building an STM in my spare time – this project has taken me all over the country and I’ve learned a huge amount.

I haven’t had much to talk about lately because:

1) I’ve been focusing on hardware upgrades that improve efficiency and speed in not-immediately-obvious ways (look for the teensy at the botom of the picture, and the shiny new chips near it).

2) Since I’m working on signal path stuff, I had a pause while my new DSO nano (at the top of the photo) shipped from overseas.

3) I’ve been completing other projects so I can refocus on the Z signal path with fewer distractions.

Thanks very much to my friends Mitch Altman, Jordan Bunker, Camo, Steve Finklestein, Ian Spielman, and everyone else who took me seriously enough to help me push this project down the road towards reality in 2010!  Here’s to a productive 2011!


X-Y redesign

In version 0.1, there was a pretty major design flaw: instead of sending -9 to +9v to the scanner head, the design I used actually sent 0 to +5v, this was noticeable in that the scanning head made almost no noise.

I’ve just completed a full redesign of the X-Y signal path and here is video (with oscilloscope proof) of the vastly improved signal output to the scanner head.

So just in time for Thanksgiving, we are a major step closer to the beta!


v.0.1.5: rebuild and bug fixes

I just finished building the version 0.1.5 machine.

Here’s what I’ve been working on during the past month and a half:


  • Fixed EAGLE routing flaws (thanks Dorkbot Chicago for a very timely EAGLE CAD class!)
  • Fixed part specification flaws (it turns out that the digital pots I originally used can’t handle much more than 8V, I was giving them 18V – oops!)
  • Built a completely new test machine from scratch, by hand (not as bad as I originally feared)
  • Started an arduino shield based design (using adafruit’s excellent protoshield as a starting point)
  • Started testing the MCP4912 DAC as a replacement for the dual 4911s, I’m currently using.
  • Switched from arduino duemilanove to freeduino/boarduino for physical design improvements (I’d like to use the UNO, but I’m waiting/hoping for improvements in the USB functionality of that board before switching).
  • Added a fast prototyping area for experiments.


  • Stopped using magnets as fasteners for the scanning head – those were awful.
  • Built a completely new physical support with improved tripd geometry and stability.

Next up:

  • Redesign the X/Y signal pathway to use the full +/- 9V range and be flexible enough to handle +/- 18V via switch and/or gain adjust (I’m only using +/- 5V now, and it’s not flexible at all).
  • Redesign the transimpedance amp pathway to improve signal/noise ratio and gain.
  • Investigate alternative approach mechanism designs.

Reminder: I’ll be showing the ChemHackerSTM version 0.1.5 at the Armand Hammer Museum in LA on Saturday afternoon/evening as part of CRITTER Salon’s Enormous Microscopic Evening.


Pining for the fjords

HELLLLOOOO POLLY!This project is not dead, it’s just pining for the fjords!

Actually, I’ve been up to my neck in:

  • rebuilding the circuit from scratch
  • debugging software
  • debugging hardware
  • redesigning circuitry

This is all stuff that is slow and relatively unglamorous.

I’ve been working frantically because I’ll be in LA next weekend showing the microscope at the Enormous Microscopic Evening at the Armand Hammer Museum in UCLA on November  6th at 4pm, and I’d really like to have version 0.2 ready for the exhibit.

I’ve learned a lot in the past month – notably that I had made a few poor design assumptions (now thankfully corrected).

Many thanks to everyone for being patient, everyone who has helped me with debugging and redesign, and to CRITTER salon for inviting me to the Enormous Microscopic Evening!


ChemHackerSTM 0.1 Schematics and Source Released w/GPL3

With a lot of help, I’ve hit the 0.1 milestone (proof of concept), so it’s time to release version 0.1 of the ChemHackerSTM designs and source code.  As the version number indicates, this is a proof of concept device — if you follow these plans, you’ll get an STM that sort-of works – no promises.

All designs and source code in version 0.1 is hereby released under GPL 3.

The physical microscope is built and works.  It’s still fiddly – I have several design improvements in mind.

The microscope’s electronics work, and will probably not change only moderately between now and version 1.

Video and source code after the jump. Read the rest of this entry »


Now for sale: Periodic Tables of the Elements

I had a lot of fun making these ChemHacker styled periodic tables – the project was very educational – both through studying the periodic table closely and learning to use Inkscape more.

They are digital prints on laminated card stock – $7 each with free shipping to the continental USA.

More details on the Periodic Table Page.

I’ll have a few samples to show off at Maker Faire this weekend!


How I etch STM tips

If you’ve been following the chemhacker twitter feed, you’ll know that I promised video of the etching I accomplished last weekend.

The video does a much better job of explaining the process than my words can:

A few notes: I made a few mistakes on the narration (it was late!):

1. The drop of “water” suspended in that steel plate is actually 2 molar sodium hydroxide (yikes)

2. Yes, those resistors are clearly in parallel, not series (gimme a break, I was tired)