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Telecon tomorrow (Thursday) @ 5 pm Eastern time

Hi all,

Telecon tomorrow (Feb. 11 in North America, Feb. 12 in Australia) at the regular time: 5 pm Eastern (2 pm Pacific, noon Hawaii, 23.00 European, 9 am Eastern Australia). Evan has found a very interesting issue with the transimpedance amp board, which strongly appears to be due to fundamental characteristics of the ADA4522-1 op amp that the board is (presently) based around. Also more news on other electronics work done by students Mike Huynh and Josh Gage, and a little bit more work on optical simulation from me. We additionally have recent updates on AIFCOMSS, and on the 144 MHz transceivers (Raveon and Radiometrix). More discussion items for tomorrow's telecon include: flight/telescope plans and tests; construction and lab tests of the new gondolas/payloads; light sources and light source modelling; goniometric and pre- and post-flight calibration; propulsion work; nanosat bus and payload solid models; computing / website / TWiki forums and e-mails; grant applications; and recap of schedules. I'll send a progress report before the telecon tomorrow.

Here's how to connect:

1) Open Skype on your computer (note that of course, you should first install Skype, http://www.skype.com, on your machine if you haven't already).
2) In the "Contacts" menu, add me ( jalbertuvic ) as a contact, if you haven't already.
3) Just wait for me to Skype-call you at the usual time (5 pm Eastern, 2 pm Pacific, etc).
4) If there is any trouble, or if you don't get a Skype-call for some reason

Here's the tentative agenda:

I) Flight & telescope plans, and upcoming tests
II) Construction, drop tests, and other tests of the new gondola and payload
III) Diffused light source and its modelling, pre- and post-flight calibration, and goniometric calibrations
IV) Solid modelling
V) Computing/website, including recent flight control and simulation progress
VI) Grant applications

Talk to you all tomorrow, thanks!!!

-- jalbert - 2021-02-11

Hi all,

My apologies for the delay! -- here's an update on recent ALTAIR balloon work, minutes of the last meeting on Jan. 14 (attendees Arnold Gaertner [NRC] and me), and a reminder of the telecon in 10 minutes(!!!) from now:

Our electrical engineer Evan Moore found an issue with the updated TIA -- the noise level and (lack of) current leakage on the board traces itself both look good with the new updated board, however the ADA4522-1 op-amp that is the heart of the transimpedance amplifier circuit (shown on page 3 of

) appears to have an offset issue at low input photocurrents, as shown in this plot from Evan:

and this writeup of this new problem (also from Evan):

Here are two photos of the test setup that Evan uses to measure the problem:

Evan tested in multiple ways that the current leakage is internal to the ADA4522-1 (removing the unguarded USB mini-B connector and inputting current directly into the traces of the board, dead-bug test inputting current directly into the ADA4522 leads, etc).

So -- how to solve this problem? The easiest/best solution, if it existed, would be another op-amp with the exact same footprint and pin-outs that has lower max input bias current (and as low, or lower, input bias voltage), but has the same (or better) noise characteristics, than the ADA4522-1. Such a chip does not exist, unfortunately. The ADA4530 has much lower input bias current (although slightly higher input bias voltage), but slightly worse noise characteristics, and the same chip size, but the main difficulty is that it has different pin-outs, which would require a redesign of the board. One alternative op-amp which does have the same footprint and pin-outs is the AD8638, which has slightly lower input bias current than the ADA4522 (40 pA max vs. 50 pA typical), although a higher input bias voltage and slightly worse noise. Evan will be trying out the AD8638 on the board as a simple replacement for the ADA4522.

For ALTAIR, we might need to make two versions of the board -- one with its board traces made for the same AD8638 or ADA4522 that ORCASat uses; and another made for use with an ADA4530 (if the ADA4530 solves this problem without making the noise significantly worse). If perchance even using an ADA4530 (with its attendant necessary board trace modifications) does not fully solve this problem, then for the alternative ALTAIR board, we may need to go for some form of differential transimpedance amplifier circuit that uses multiple op-amps to cancel out the input bias current and bias voltage in the pair of op-amps that form the input of the circuit (yet of course retains the linear transimpedance amplification of the original TIA circuit), such as was done in, e.g., this 2019 publication from some electrical engineers at Beihang University in Beijing:

We got quotes on a 1 MOhm metrological calibrated resistor (also to aid in testing and cross-checks), but neither of the two Canadian manufacturers of metrological resistors (Guildline and Measurements International) responded to the UVic RFQ! (IET and Fluke, the two U.S. manufacturers, were the 2 responders to the RFQ, but the quotes were both too high.) Our students will send a e-mail to the presidents of Guildline and/or Measurements International to see if we could partner with them and thus hopefully get a good deal on a 1 MOhm metrological resistor.

I've begun to look some more at MEEP (https://meep.readthedocs.io/en/latest/) for finite-difference time domain (FDTD) simulation of integrating sphere output, but I haven't yet had time to make any significant progress there -- I'm hoping to do that in the next couple of weeks. It will be interesting to compare that with ray tracing simulations, when I can get a chance to do that!

Radiometrix still has our four SHX1-144 transceiver modules (they arrived there on Apr. 6) and is doing their firmware update that solves the BUSY output issue. They'll then test them out and send them back to us. Due to the COVID-19 situation in the UK, they've been taking a very long time; the UK is enduring its second wave of COVID, and with new even-more-highly-transmissible COVID variants now, and the country is still under a lot of restrictions as a result. Our department electrical engineer Nick Braam sent them last month (on Monday, Dec. 14) an e-mail to check up on when they will (finally) be sending the firmware-updated SHX1 modules back to us, to which they still haven't replied. (We'll send another check-up message in February.) In the meantime, we've also been doing more connecting up and testing out of our two new 144 MHz Raveon M8S data modem transceivers here in Victoria:

After checking them out with Raveon's Windows-based Radio Manager software, I've started to connect the radios up to Arduino Megas -- in the next few weeks I'm planning to get them talking to one another, and then I'll check out their effective ranges.

Once we get those 144 MHz transceivers settled and back into the ALTAIR gondola, we'll do some outdoor drop testing of the actual gondola. (We've done all the outdoor drop tests I can think of doing with our dummy gondola.)

And we also still need to test out our new DFRobot SEN0177 payload aerosol monitors that we have here:

Engineering students Josh Gage and Evan Moore found that the "wings" that Josh had found in the laser diode light output distributions:

were due to how the diode was mounted in the heat sink. When the diode is mounted properly and carefully, the wings go away.

We also have our 10 Hamamatsu S12698-01 photodiodes and 3 Thorlabs FDS100-NOCAN photodiodes (those Thorlabs ones have their windows removed) here in Victoria:

I've given them to Evan to try out -- he's taking a few weeks to ramp up, and will produce some linearity, etc., plots from them soon.

The survey-tripod-mounted device to cross-check yaw-pitch-roll information from the gondola (e.g., on days before/after flights) is also constructed now, thanks to Mark Lenckowski -- photo at:

and all that remains to be done is to finish the small fitting between the device and the bottom of the payload. The purchased hardware in it includes both the survey tripod (http://www.cpotools.com/cst-berger-60-alwi20-o-aluminum-tripod-with-quick-release--orange-/cstn60-alwi20-o,default,pd.html), two adjustable angle mounts (http://www.thorlabs.com/thorproduct.cfm?partnumber=AP180), and a rotation mount (https://www.thorlabs.com/thorproduct.cfm?partnumber=RP01). That last fitting to attach (temporarily, pre-or post-flight) the upper adjustable angle mount to the payload landing gear has been started and will be completed here in the next couple weeks.

We're currently revising the draft initial contractual agreement from our colleagues at Globalstar Canada regarding 2 initial SPOT Trace devices (and their service plans) for the educational side-project for the upcoming NATO SPS application, in which classrooms in elementary and high schools could launch company-donated SPOT Traces using party balloons (or a more environmentally-friendly version thereof), and track them to learn more about winds at different levels in Earth's atmosphere.

Houman will send Cordell and/or us updated sections of his master's thesis soon -- that information will be extremely useful to us going forward. Also, Susana and Nathan, it would be very helpful for us all to get the JHU students' final writeup when you have a chance.

Next grant application will be a NATO "Science for Peace and Security" application (together with Australian colleague partners).

Our next telecon is in 10 minutes from now -- see below for Skype instructions.

Cheers, talk in 10 mins (!!!) from now -- thanks all!


-- jalbert - 2021-02-13

Title Telecon tomorrow (Thursday) @ 5 pm Eastern time
Forum ForumGeneral
Topic attachments
I Attachment History Action Size Date Who Comment
JPEGjpg 20210204_145816.jpg r1 manage 581.9 K 2021-02-11 - 22:17 JustinAlbert Evan Moore TIA offset error test setup (Feb. 9, 2021) photo #1
JPEGjpg 20210204_145824.jpg r1 manage 898.2 K 2021-02-11 - 22:18 JustinAlbert Evan Moore TIA offset error test setup (Feb. 9, 2021) photo #2
PDFpdf DifferentialTransimpedanceAmplifier_oe-27-3-2125.pdf r1 manage 3654.1 K 2021-02-11 - 22:15 JustinAlbert Differential transimpedance amplifier circuit article (S. Zhang et al, Optics Express 27, 2125 (2019))
PDFpdf EvanMooreNotesOnTheTIAOffsetProblem.pdf r1 manage 937.8 K 2021-02-11 - 22:12 JustinAlbert Notes on the TIA offset problem from Evan Moore (Feb. 9, 2021)
PNGpng offset_error.PNG r1 manage 34.2 K 2021-02-11 - 22:16 JustinAlbert Evan Moore TIA offset error plot (Feb. 9, 2021)
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Topic revision: r3 - 2021-02-13 - JustinAlbert
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