Derek,
I've been meaning to respond here for awhile - but one thing and another... however, I've used the time to put together a checklist of items I wanted to cover, so the delay isn't exactly wasted.
It has been brought to my attention that the ebay seller who sold the UP501 gps module is currently out of stock. I don't know if this is a temporary issue or not.
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If you find any other vendors selling the UP501, please share here.
Thanks!
Item 1)
As to the lost availability on the 501, it went away on 28 April - as I was watching this listing practically every day - watching the quantities and figured once they got below 500, I'd go ahead and jump in -- then, the next morning, "Listed ended". Caused a slight panic, but I searched around and found this other listing:
https://www.ebay.com/itm/High-perfo...GPS-Antenna-Module-For-Arduino-/151289895145?
... and jumped in that morning (4/28) and bought the two you see listed as 'sold'. I'm actually rather incredulous that they have'nt sold a single one since then (well, I'm getting both available and no longer available, depending on two different links) - except that this listing doesn't show up in a search (don't ask me how I found it - too long ago), so maybe no one knows about it. At any rate, there still seems to be a little availability (at the $22 price). Arrived something like 10 days after ordering. Maybe the link will work for those interested.
Item 2) - testing for shorts:
I think common sense could probably help here and, while I'm moderately capable in electronics assembly, I might would respectfully ask for a few pointers on this - just to make sure I wouldn't leave some 'bomb' ready to go off once I install the major components. I assume metering the connection points for the major components (Vcc, etc) to verify correct voltages would be smart - and checking the LEDs etc (as you've already noted). Mainly, just a pointer or two on things to NEVER let happen in the passive component assembly might allay some of the fears.
Item 3) - Breadboarding the GPS unit:
I've got a few breadboards and have picked up a USB-to-UART module or two - one based on the FTDI chip:
https://www.ebay.com/itm/1pcs-Bluet...ter-Compatible-Xbee-for-Arduino-/141303235098
... and another based on the CP2102 chip:
https://cgi.ebay.com/ws/eBayISAPI.dll?ViewItemVersion&item=141238861134
(this board has both 3.3v and 5v outputs whereas the FTDI board is just 5v (not useful unless I put a voltage regulator/limiter in-line with it, I understand))
Having never really ventured into this 'part of the woods', I was thinking of rigging them up and grabbing the GPS workbench and simply tinkering with it thru my laptop a little before mounting on the boards. Do you see any problems with this? Any cautions about those boards (or those chips) (other than making sure we're on 3.3v for the supplies)?
I was also thinking of doing the same thing with the Bluetooth board, but we'll get to that another day.
Item 4) - Mounting the active components:
I'm really leaning towards mounting the active components (on the transmitter, at least) on sockets rather than soldering directly to the PCB. There may not be any real advantages to it, but I'm trying to think ahead to a time (hopefully never to arrive) when I might have to salvage things in the aftermath of a crash. I'm aware that the RX is rather tight, spacewise, and probably can't accommodate socketed mounting, but the TX isn't so constrained (my initial plans are for a 3" vehicle, so we've got space to spare). Thoughts? Also, is it possible to do this on the RX? (low profile sockets - I've seen some, but don't know how low)?
This for the XBEE (Digi's recommended model):
https://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=153931614&uq=635420112306685323
... and this for the GPS:
https://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=153931604&uq=635420112306841333
... which mates to...
https://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=153931605&uq=635420112306685323
I am aware that the two 'feet' on the GPS are meant to solder down to the PCB to better anchor the unit -- but figure I might could fab some 'standoffs' out of brass rod (on my little lathe) to act as spacers (silver solder (higher temp) to the PCB such that it wouldn't come loose when soldering (regular solder) the GPS to the standoffs). Not sure, tho, if that higher temp silver solder could lift the pads on the PCB. Should I contact OSHpark on that? (the boards are already in)
Item 5) - XBEE radios:
From what I understand (which may not be much), the 200Kbps radios support the Digi-Mesh protocols and the 10Kbps supports the P2MP (point to multi-point). It would seem (thinking down the road) that the Digi-Mesh would be a decent capability to have - set up some repeaters out at the fringes of the (rocket) range (say, at 4 points on the compass) and this would enhance the range of all devices in use. I can understand getting the increased range with the 10Kbps radios - especially since that data rate would have plenty of headroom for this present application. Is Digi-Mesh a possibility with these "-001" radios? (I just may not fully understand the differences).
Item 6) - offline maps:
Can you (or some of the other readers here) review what is necessary to utilize offline maps. I've been doing a little digging over on Google Earth, but am new to this (it appears this is just maps only - satellite imagery isn't available, as I read it - but my knowledge of this is very preliminary).
Item 7) - Hammond case:
Looks like there's 2 sizes of cases for the RX - you're wanting the small one, correct?
Item 8) - Batteries and ground support:
I went a little larger on the batteries - a 950mah for the TX and 750mah for the RX - just thinking increased operating time (mainly for the TX). I was also wondering if some 'GSE' (ground support equipment) to keep the electronics 'topped off' until actual first motion - maybe utilizing something like a mini stereo plug from some larger battery on/under the pad - feeding a 'power bus' throughout the rocket - and pulling the plug upon lift off. Is the assumption of feeding the power in parallel like this a valid one? I was thinking of just soldering two of the JST connectors to the power inputs to the TX - and utilizing one to feed normally from the battery and the other to plug in to the 'power bus'. Is this workable?
Also (which this seems similar), can the RX be charged while also being in use? They make several of the 'power modules' utilizing the 18650 LiIon cells (for your cell phone, etc) that outputs 5v thru a normal USB jack - just a normal USB charging cable to the RX would be all one would need (if this approach would work). May not be necessary, but on a long 'hunt', knowing one could simply plug in this aux power would be nice to know (beforehand).
Item 9) - SMD soldering practice:
As to those needing a little practice (or exposure) to SMD work (me), I found this rather decent little 'practice plate' that is quite economical and gives enough items to practice on that one should be rather expert by the time you get to the actual boards (it's actually about 50c cheaper than when I bought it):
https://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=281134843051
Item 10) - Good deal on LiPo charger:
Stumbling around out there in cyberspace, I found this rather decent deal on a 1S LiPo charger:
https://www.allerc.com/thunder-power-tp103cq-acdc-1s-lipo-quad-4-port-12v-ac-dc-charger-p-5913.html
... a 4 port, AC-DC charger at a clearance price (I verified that Amazon sells these at the higher price). I called them and they explained they are discontinuing the Thunder-Power line - and had 3 of these in stock (2 now, I guess, since that was before I ordered). Shipping from these folks is about $5. The only issue here is that the charging port connector is this 'Ultra-Micro' connector - not the JST-RCY that the standard batteries use (why they can't call these connectors by the Mfr's name, I don't know) - but the bottom line is the *actual* name of the connector is the Molex 'Pico-Blade' (Digi-Key has them). If you are not interested in making your own adapter cables, some are here:
https://www.rc-connectors.com/index.php?main_page=product_info&cPath=66&products_id=350
... but, for $6 ea, I'd rather buy a crimper and make my own.
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That's enough for now - thanks again for this nifty little project, Derek. Haven't even started soldering yet - just gearing up and getting the parts together.
Hope this wasn't too long with too many questions.
-- john.
HY capabilities of the module, and each set of modules will be specifically paired to each other via the unique SNH/SNL's of each radio. Even with this step, there will inevitably be potential packet collisions when multiple "Xbee-Backbone" systems are in play at a launch. Those conditions are detectable at module level, so I'll be strategizing how to deal with those instances using back-off randomization, etc... Hop table tweaks are also an option, but at this time I don't anticipate going there.
