Telecon tomorrow (Thursday) @ 5 pm Eastern time

Hi all,

Telecon tomorrow (Oct. 15 in North America, Oct. 16 in Australia) at the regular time: 5 pm Eastern (2 pm Pacific, 11 am Hawaii, 23.00 European, 8 am Eastern Australia). Electrical engineering student Evan Moore now has the new update to the transimpedance amplifier boards for the photodiodes to add the needed guard ring (and other updates) -- a rendering can be found here:

the new schematic is here:

and we plan to fabricate this new board next week. 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 and would like to join, please just send me an e-mail (jalbert@uvicNOSPAMPLEASE.ca).

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
VII) AOB

Talk to you all tomorrow, thanks!!!
justin

-- jalbert - 2020-10-14

Hi all,

My apologies for the delay! -- here's an update on recent ALTAIR balloon work, minutes of the meeting two weeks ago (attendees Arnold Gaertner [NRC], Liviu Ivanescu [Sherbrooke], and me), and a reminder of the telecon in 20 minutes(!) from now:

As mentioned in the meeting announcement e-mail yesterday, electrical engineering student Evan Moore has created the new layout & schematic for the update to the transimpedance amplifier boards for the photodiodes to add the needed guard ring (and other updates). You can compare the new schematic here:

with the previous board schematic here:

and here are all the renderings of the new board design:

and the mask and plating traces on each of the 4 layers (from top on down):

I asked Evan the following questions, and got the following good answers, on the design update:

> > 1) What is the empty white rectangle on the back of the board (i.e., on
> > the channel 2 side of the back of the board) there for?
> 
> 1) That is a spot to put a sticker, so that we can individually label each part (much like Andrew did) to keep track of systems that pass
> tests.
> 
> 
> > 2) Should the metallized vias around the guard trace be blind (i.e., only
> > down to the connections with the guard plane, rather than being full
> > through-holes), just to avoid the possibility of coupling some
> > additional noise into the guard from the power layer and/or from the
> > back of the board?  (Or would that add a lot of unnecessary expense in
> > fabrication? -- if that's the main reason not to do that, then how much
> > extra would it cost?)
> 
> 2) We are switching fab houses to OSHPark since doing so gets us better
> manufacturing tolerances at essentially half the price of PCBWay. The
> drawback of that is they do not do blind/buried vias for their prototype
> runs (which is what we would be getting). So to add them would make the
> costs of the board drastically higher.
> 
> 
> > 3) For the bias switch, why did you change from a TMUX6119 + OPA189 driver
> > to an ADG1419BRMZ?  Was/is it just for simplification purposes, so
> > that you have just one component, rather than two?  If so, have you
> > already tested an ADG1419BRMZ there (via some breadboard connection or
> > somesuch), just to make sure that this won't cause any unforeseen
> > problems with noise etc?
> 
> 3) I had to remove the OPA189 serving as a buffer for the TMUX6119 since
> it was getting saturated when you applied the reverse bias to its input
> (we could only power it with 6.2V but we were trying to push 9V through
> its input, definitely would not have been good times there). I also
> could not have used the 9V reverse bias itself to power the OPA189
> buffer, since it requires at least some headroom to operate (creating a
> dedicated voltage rail just for this is obviously out of the question,
> and I also could not just tie the raw 10V supplied from the EPS to the
> device since the PSRR of the OPA189 is not high enough at our switching
> frequency to clean that up on its own).
> 
> Consequently I went to a MUX with a low on-state resistance (hence the
> part change there). This device is also fully specified for the voltages
> we will be giving it (where as the TMUX6119 was operating at the extreme
> low end of its range at 9V, and was pulling a lot of q-current to make
> up). The low on-state resistance saves us from the issue of having no
> buffer, since the voltage drop across the device is extremely low (2.1
> ohms * 4mA max gives about an 8mV drop in the worst case, not nearly enough to forward bias the photodiode in the case of no reverse bias
> being applied).
> 
> I would still like to verify this part works as expected so I will be
> putting a few of these onto the next digikey order that rolls out of
> here.
>
>
> > 4) Similarly, was the removal of the trim pot from the LT3045 bias
> > generator just for simplification purposes? -- and if so, have you
> > *explicitly tested* your exact new configuration with the present board
> > (via point-to-point connections with a breadboard)?
> 
> 4) The trim pot was to allow for us to manually adjust the reverse bias
> voltage applied to the photodiodes. If you look at the LT3045 datasheet
> (the device I am using to generate the rail voltages on the TIA as well
> as the reverse biases), it adjusts its output voltage based on the
> resistance applied to on of its pins (i.e. where the trim pot was). I
> have confirmed that this does work since the other LT3045 supplies the
> board 6.2V rail with no issues. But for sanity's sake I did also measure
> that the reverse bias generators work up at the 9V they need to supply
> (in order to make 4V above the 5V floating GND the photodiodes are at),
> and they do that without any trouble.
> 
> 
> > 5) Also, why the change in the PG & PGFB settings, and in the SET
> > capacitance, on the LT3045 bias generator?  Have all those new settings
> > been explicitly tested, using the present board?
> 
> 5) The PG/PGFB is used to drive the "fast startup" mode of the LT3045.
> Right now - without the PGFB resistors - the device take about 12
> seconds to charge up to its voltage rails (due to the large capacitance
> on the SET pin and small driving current through this pin). In "fast
> startup" mode this changes to a 2mA driving current until a threshold is
> reached, so the device boots much faster. This mode is recommended in
> the datasheet, and I followed the design guidelines for it (as well as
> the layout pattern). If it really does not work for us, we can
> depopulate the PGFB resistors and jump the PGFB pin to VIN.
> 
> 
> > 6) Could the addition of the C17 capacitor to the REFOUT of the ADCs
> > potentially cause similar noise problems to the problems you saw with
> > noise due to the C21 capacitor on REFP0 (in the design of the boards
> > you presently have)?  Have you actually tested having a capacitor
> > there, using the present board?
> 
> 6) Conversely, the addition of a capacitor to this point actually stabilized the internal voltage reference of the ADC (recommended in the datasheet, and verified in
> testing). This point is detached from the REFIN pins (since it is attached to the internal voltage reference), so there is no chance of it causing oscillation on that
> input. I also compared the noise readings and confirmed that using the external voltage reference is still better than the internal one, but we can always swap to the
> internal one on the fly by just changing a register value.
> 
> 
> > 7) What is TP6 on AIN3 of the ADCs for?  (Would that be to test the
> > application of an input voltage there? -- since I don't think there
> > should ever be any possibility of an output there, correct..?)
> 
> 7) This point is essentially just a backup solder pad, if we want to do
> something wild like have each ADC be able to measure both photodiodes,
> then we can solder a lead to this pad.
> 
> 
> > 8) Are there any possible ramifications of no longer having the 2.4 volt
> > supply?  (Why was that supply there in the first place? -- I forget.)
> 
> 8) The 2V4 supply was there to assist my attempt to make the PGA useful
> to us. The PGA has very strict input voltage limits, which the normal
> 5V0 full scale range of the TIA would exceed. That's why I had the
> switchable input voltage reference on the TIA as well in the old design,
> to drop that down to 2V5. The 2V4 reference would then give us the small
> amount of differential headroom that would let us see our full range of
> positive/negative byte codes when using the PGA.
> 
> This is why I removed all that, because it was complicated and
> ultimately didn't give us any useful functionality that we couldn't get
> with the relays.

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 long time. Very fortunately, the COVID situation is slowly starting to improve in the UK (although everyone is of course very wary of a likely second wave). I asked Radiometrix about this yet again on Monday, and they haven't replied yet. 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 20 minutes (!!!) from now -- see below for Skype instructions.

Cheers, talk in 20 mins (!) from now -- thanks all!

justin

-- jalbert - 2020-10-15