Open Notebook 1

This is an experiment with opening my research notebook to the web.  I’m keeping my notes in an Evernote notebook, but I’m going to post lightly edited (i.e. remove personally identifiable information from people I talk to unless they give me specific permission).

Keep in mind that these are my raw thoughts for the past two months, with no editing for accuracy.  Follow these notes at your own risk.

11/03/2011 (Purchase Notes)
Purchased from Newark ($62.46 + shipping):
* 3 DAC8554 (TSSOP-16 packages)  quad 16 bit DAC
* 3 REF02 (DIP-8 packages) precision 5v reference
Purchased from eCrater user fcpcb ($11.44):
* 5 TSSOP-16 to DIP adapters

10/31/2011 (Denver/Boulder Notes)
met L. M. (physicist) at Solid State Depot hackerspace meeting – he built an STM as part of his PhD work:
* L. M.’s STM had a higher cost (and precision) than the chemhacker STM, but a lot of his designs and thoughts can be adapted to fit a cheaper device. Also, he’s excited by the idea of an open source STM project.
* need more bits on the Z DAC
* * 10 bits gives ~17.59 mV/step which is ~2.81 nm /step (at ~0.16 um/volt) that’s so large that the needle will pass into and out of tunneling in only one step.
* * 16 bits gives ~0.2747 mV/step which is ~43.9 pm/step, small enough that you can control tunneling with more than one step.
* * 16bit DAC notes:
* * * DAC8554 from TI is a 4-channel ultralow glitch DAC
* * * $10-15 each: pricey, but handles all four channels at once, not much more expensive than 4 of the microchip DACs I’m using
* * * SPI interface, unsure if it differs from the microchip SPI standard
* * * TI recommends a REF02 precision 5V voltage reference (~$3-4 each) – probably a good idea to try this out
* * * downside: no DIP package available – surface mount only
* probably need a better/faster micro controller
* * suggest that PID loop be accomplished at about 20MHz
* * suggest the Maple from Leaf Labs
* * * 12 bit ADCs (versus 10 bit for arduino/teensy)!
* * * 47 MHz versus 16MHz for arduino/teensy
* * * the IDE looks almost exactly like the arduino IDE.
* * * I’ve spoken to Leaf Labs folks in the past, they’re a good group of quality-focused engineers/artists.
* * * purchased on 10/30/2011 should arrive in a day or so via USPS
* thoughts on the sample bias voltage
* * since sample needs only ~10 millivolts, it’s probably best to just pass the DAC output through a pair of unity inverting amps (don’t remove the DC bias).
* * then, put the two outputs (positive and negative outputs) to a manual switch so the user can choose a positive or negative sample bias (allows future expansion to negative sample bias)
* * with a 16 bit DAC, it’s pretty easy to select ~10mV (just set DAC to ~4 and leave it there)

10/20/2011 (Nanotech conference notes)
Questions for people who know more about SPM than I:
* Is Gwyddion well-regarded in the microscopy arena?
* How do you make HOPG / graphene? Is it at all easy?
* What is an appropriate sample bias for starting? I saw ~10mV today, but I was going to use ~1-2V, that’s bad.
* Is there a market for STM tip-making machines?
* What is the process for making an AFM tip?

10/19/2011 (prototyping notes)
* added 2.5V and 5V voltage regulators to clean up voltage signals
* fixed clipping problems by lowering the gain resistor from 36k (predicted by the formulae) to 27k (as determined experimentally)
* fixed non-symmetrical behavior by applying correct ground to the 2.5v and 5v regulators (their grounds were floating a little higher than true ground)

10/10/2011 (Purchase Notes)
Purchased from Newark ($43.69)
* +9v, -9v, +5v, +2.5v voltage regulators
* piezo elements
* 0.1uf, 1uf, 0.33uf capacitors
* tunneling op-amps

CHEN chapter 11.1: desirable tunneling amp design: 1V/1nA

Idea: change op amp gains such that the electronics use ground, +5v, +12v, -12v >>same as supplied by ATX power supply
Test: test ATX power supply with oscilloscope to check cleanliness of signal (should be pretty clean, right?)

…actually, can use these power supplies now without changing the gains…


5 Responses to “Open Notebook 1”

  1. Nick says:

    Interesting call on the Leaf Maple. I’m not an Arduino guy, but have done some work with Cortex M3 micros and been very impressed. Lots of power and features, although I am not averse to writing code in C. You might also look at the newer Cortex M4 parts, like the STMicro STM32F4. They have much higher clock rates, 168MHz, onboard 12 bit ADCs and DACs, lots of SPIs and UARTs, hardware floating point and DSP features, as well as built-in Ethernet which I imagine could be really useful for moving data to and from the scope if and when you get to the point of doing a custom PCB. That part could be really interesting as with a network link you could run a web server on the scope and have a browser-based UI/viewer, something like that. ST sells a Cortex M4 Discovery Board that you can get for around $15. The tools are not going to be so nice though, there is an Eclipse-based IDE but the free version limits the size of executables you can build. Otherwise it’s big $$$ for tools or GCC and Make, which makes things more complicated.

    One tip I would offer, if you haven’t already used up your goodwill with the IC manufacturers, is that you can request free samples from the likes of TI, STMicro, etc. It’s really easy to do, most of them have a sample shopping cart you can fill up while browsing their websites. I’ve had great luck doing this as an anonymous hobbyist, and since your project is actually really cool and has a public face, they might be happy to help with samples for the publicity. If you just want to get one or two of something to try out, this is the way to go over racking up $20 or $50 at a time on little batches of stuff from Newark or Digikey or whoever.

  2. Jared says:

    I’m just curious if you ever finished the version 0.3 firmware.

    • Sacha says:

      Once I realized the problems with 0.3, and the fact that I had to change to the Maple platform, I stopped development of that firmware. 0.4 will theoretically have a fully functioning firmware.

  3. Rcfly says:

    Would love to see a new notebook post about your current progress! Was neat to see into how your tackling the design.

    • Sacha says:

      I’m certainly planning to, but I’ve been stuck on some annoying SPI communication issues for a bit. As soon as I have something new to talk about, I will!