Single-Board Universal Module

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27 Mar 2015 15:26 #30331 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
I Can't get the sky switch to work. I'm sticking with the peregrine switch which works great. And no, I haven't even thought about the HID option. I'm not sure I'll ever develop it, unless I see real interest. The current issue with the board is the following: The board is supposed to enter programming mode when powered up from USB, but not when powered via 5V from the PPM or Devo connector. That is done via diodes separating the input supply from the 5V reference used by the LDO. The USB supply is hooked to the BOOT0 pin of the MCU with a pull-down resistor attached. So when power is supplied via USB, the BOOT0 pin goes high, and the MCU enters programming mode. When powered via 5V from PPM/Devo connector, the BOOT0 pin should be held low via the pulldown resistor. But it doesn't work reliably. Disconnecting the jumper isolates BOOT0 from the USB supply, and the MCU properly enters execution mode. I just don't yet understand why the circuit isn't working as expected. Possibly there is too much capacitance on the USB supply and the resistor can't dissipate the current quickly enough. I'll put a scope on it and maybe see what is going on.

I've looked at manual P&P machines. I'm actually holding out for an automated one (something like the FirePick) though nothing on the market yet. But that won't help at all here. As I've said before, I am not willing to sell these myself (at least not within the US). The risk is just too high unless I can get it licensed, and I can't see how to justify the cost of licensure. So our best bet is to try to find someone to produce and sell them without my involvement.

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27 Mar 2015 15:31 #30332 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
Thanks SadSack for that low-budget P&P example. I might do something like that. It looks easy and cheap and I probably have 90% of the stuff I'd need for it around already. It would probably hold me over for quite a while.

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27 Mar 2015 15:51 #30333 by moss
Replied by moss on topic Single-Board Universal Module
I do not quite know how this is intended to work, but Schottky diodes have reverse leakage that may upset the applecart.
You could add 1K or less shunt on either side of the diodes, to reduce the leakage until it makes a logic "low" voltage wherever it ends up. Or you could use "real" logic with FETs rather than diode logic. Low leakage diodes is an option.

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27 Mar 2015 16:35 #30334 by SadSack
Replied by SadSack on topic Single-Board Universal Module
Use real slide rails. Guy did have minor issues with weight. 8mmx300mm rods (off cuts) very cheap. I put together rods and slides for 3 axis under £20. If I ever get my windows tablet back that will drive USB microscope and or eagle. And small halogen oven 3 boards fit! And with witness strip should get some speed placing! Chinese sweat shop comes to mind :-))

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27 Mar 2015 16:53 - 27 Mar 2015 17:36 #30336 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
need a low voltage-drop over the diode, which is why I used Schottky's in the 1st place. The board needs to operate with a voltage as low as possible. With the Diode and the LDO, that leaves me little margin in the design. The Diode specs list reverse current at 1-5mA. The boot pin must be under 1.6V (probably better under 0.7V) at power-on to ensure it doesn't trigger the programming circuit. using the Shottky is not going to work well here no matter what I do. However, I only need the low Vf drop on the PPM/Devo supply side. On the USB side, I am guaranteed 5V, so I can just replace the USB-side diode with a general-purpose diode with Vf ~1V and <100uA reverse current and probably be good to go.
Last edit: 27 Mar 2015 17:36 by PhracturedBlue.

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29 Mar 2015 23:02 - 30 Mar 2015 00:34 #30424 by octagon
Replied by octagon on topic Single-Board Universal Module
Can you use two LDO's? Some may prevent reverse flow sufficiently.
If only one power source is needed, at a time, can the other source be switched off, using maybe SC-70 load-switches, or enable pin?
What is max current draw? Can you use a dc/dc from transmitter to extend battery life (noise?)?
There may be better LDOs but this one simulates isolation of the sources from each other.

Among many choices of LDO's for this, the CMOS PMOS proably will not work due to the intrinsic drain body diode, so bipolar output may be the only choice, along with "high" ESR tantalum, aluminum, or niobium output caps.
Most LDOs are not bipolar output but this one is: 1016-1873-1-ND and is also low cost fixed 500mA SOT23-5.
"Reverse Battery Protection" is usually not a feature of MOS LDOs, except 893-1175-1-ND which is designed with this in mind. 700mA low ESR OK, but max 6V in. SOT-89-5 is also smaller than the 1117 and its "tab" is grounded so heat-sinking to ground-layer should be better.
The 1117 types are usually also bipolar, if you have the space for 2.
Attachments:
Last edit: 30 Mar 2015 00:34 by octagon.

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30 Mar 2015 00:15 #30427 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
I think that is overkill. I looked at it with my scope, and I'm only getting 2V on the BOOT pin. The current solution would actually work fine for me with a 1k resistor, but I don't have much confidence in it at all temperatures. For the next iteration, I'll likely use this LDO:
www.digikey.com/product-detail/en/BA33BC...C0FP-E2CT-ND/3663735
with this diode (only for the USB side):
www.digikey.com/product-detail/en/RB160M...B160M-40CT-ND/926504

That should allow a lower input voltage (on the ppm/devo side) and only allow 30uA current through which can easily be handled by a 10k resistor.
I've been working on the Android app and PPM output this weekend. All of the settings are implemented. I just need to get binding coded, and I'll be ready to go.

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30 Mar 2015 00:48 - 30 Mar 2015 00:49 #30431 by octagon
Replied by octagon on topic Single-Board Universal Module
Never overkill unless too expensive. I may revisit some old design I worked with DC/DC that worked very well. Is 3.3V from 5V, (66% efficiency) important? Over 90% should be attainable with a DC/DC. Battery life? TX PA is the main load on the battery I'd guess.
Is 2V a logic high?
My last edit with the Torex LDO should have very low drop-out, I wish I never used the 1117 series, tab is "hot", and heat-sinking thru bond-wires and epoxy is not so good.
I never considered Dpak for this but that gives you more choices.
Last edit: 30 Mar 2015 00:49 by octagon.

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30 Mar 2015 00:54 #30432 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
both cost and board area are critical for this board. I looked at dc/dc converters, but they are a lot more expensive and do not generally suppot as much range in Vin

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30 Mar 2015 01:08 - 30 Mar 2015 01:24 #30433 by octagon
Replied by octagon on topic Single-Board Universal Module
Do you really need 700mA max? Did you measure current draw with some antenna mismatch? PA takes "100mA" and CYRF 40mA max, CC2500, A7105, half that, nRF less.
Maybe 500mA LDO will be plenty?

DC/DC 600mA 6V max
www.digikey.com/product-detail/en/NR4018...87-1671-1-ND/1008286
www.digikey.com/product-detail/en/XC9236...93-1162-1-ND/2512403
$1.20 plus two caps.
Last edit: 30 Mar 2015 01:24 by octagon.

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30 Mar 2015 01:34 #30435 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
my current solution will work passed 15V. I don't know if I'll ever need it, but users have been known to use 7.2V batteries which could get passed to the LDO. I'd use a 500mA LDO if it actually gave me a benefit. I haven't seen one that does though. I haven't measured the power yest (really should), but I think I estimated max current at something like 230mA.

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30 Mar 2015 03:49 - 30 Mar 2015 04:34 #30438 by octagon
Replied by octagon on topic Single-Board Universal Module
The schematic said 5.0V so I thought that was already regulated.
TI has a little integrated controller, that can handle up to 17V, looks pretty good but a few cents more.
www.digikey.com/product-detail/en/TPS621...6-29879-1-ND/2781002
www.digikey.com/product-detail/en/BRC201...87-2905-1-ND/2649025
$1.64 plus caps.
Higher efficiency (close to 90%) also means less heat on that board being burned off. 7.6V - 3.3v x 0.23A = 0.99W

Exar Corporation SPX3819M5-L-3-3/TR takes 16V in, a bipolar LDO 500mA. typ 220mV dropout at 250mA. www.digikey.com/product-detail/en/SPX381...16-1873-1-ND/3586590 An LDO on the USB +5V rail may allow the 6V max type.
Last edit: 30 Mar 2015 04:34 by octagon.

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30 Mar 2015 04:48 #30440 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
That is a good find. I'm not sure I want to add a dollar to the board cost just to save power in a non-typical usage case. In almost all operating modes, I can rely on the input power to be 5 to 6V. Allowing variance in supply voltage is important, but I'm not yet sure I want to optimize for it.

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30 Mar 2015 07:38 #30444 by Fernandez
Replied by Fernandez on topic Single-Board Universal Module
I use these cheap chinese switchers a lot, with great succes, chip used are MP1584 or MP2307.

www.banggood.com/5Pcs-Mini-DC-Adjustable...Module-p-952402.html

For a low current voltdrop, (but stable), use a zener and resistor, it is better than a diode in series.

With regards to production, do you have royaltees/rights? Otherwise, I think hard to beat the plenty of chinese rc manufactuars and the modules could be in stores soon and cheap, low margins?


I think the deviation project is excellent!
I beleive the future is full digital like deviation, I avoid ppm and just nice to use with your old Tx.

I beleive in truly open diy Tx platform, basically a market generic ARM board, PI, Beaglebone, Mbed etc etc board with plenty of IO and features onboard, as audio out, imu .. There are plenty cheap baords on the market. Board can be hooked up wired to all pots and switches in you TX of choice, connected to the universal tx module. (in addition many possibilities for expansion hooking up additional modules etc)


As such there would be a powerfull universal Tx deviation platform opening up to much more diy people and lead to stronger software development. There are plenty of creative or crazy ideas which could be made possible. In that case only limetid by software, not anylonger by hardware developed by Walkera.

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30 Mar 2015 13:05 #30456 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
The diodes are there to isolate the 5V USB from the other external 5V supply. That is needed for 2 reasons: 1) allow the oard to go into programming mode when powered by usb but not by normal power without setting any jumper, and 2) allow programming without reverse powering the transmitter via USB. I like this design, and think I can make is work, so I'm panning to keep that aspect. Still Waffling on the LDO vs DC/DC though.

There are no royalties or rights to be had. The design is entirely open source. But I only have limited contacts. Finding someone to sell them will be critical. China seems most promising, but really anyone outside the US will probably be fine. I could do it myself for anyone not within the US, but my market is probably mostly here, and I'll need at least some volume to bring costs down.

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30 Mar 2015 13:28 - 30 Mar 2015 14:58 #30462 by moss
Replied by moss on topic Single-Board Universal Module
MP2307 is a nice chip, but sells for a dollar more than the TI controller in the US. It is also lower frequency and thus needs a larger inductor, and SO-8 is a bit larger (5x6mm) than the 2x2mm TI chip. The TI application circuit also takes less parts than the MP2307, and will work at lower voltage. The TI chip can use a an 0805 size inductor.
The TI part will go to 100% duty cycle while the MP2307 will go to 90%. This is a good point in battery operated equipment where you want to maximize battery use. MP2307 will work with higher current, up to 3A, and does not look to be optimal for this application.
Using a switcher carries some risk in that the switching noise needs to be understood and tolerable, and/or more filtering may be required. I would look at spectral sidebands for eventual Vdd noise injection. A higher switching frequency will probably be easier to filter out, using smaller inductor. (approx. -50dB with a 2.2uH + 1uF LC filter, if needed)

If battery-life is a priority the TI switcher plus an LDO on the USB rail could work.
Last edit: 30 Mar 2015 14:58 by moss.

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30 Mar 2015 15:59 #30469 by mikemacwillie
Replied by mikemacwillie on topic Single-Board Universal Module
Personally, I don't think it's unreasonable to expect people using it outside of the standard use case to pre-regulate their battery voltage with a switcher. In this use-case you'd also get the added benefit of the LDO removing a good portion of the switching noise.

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30 Mar 2015 16:24 #30470 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
I really need to measure input current. If my 230mA number is accurate, I may really want the DC/DC supply. none of the LDOs I've looked at could get up to 12V (which is my target maximum Vin) before hitting their power dissipation limits. To find a part that would do so, I'd end up at the same cost as the TI part. The TPS62172 should be able to run down at around 3.5V and still have good stability and will be able to run at 12V at my estimated current. Even from China, I can't get a great price break, so it will add over a dollar to the board cost. I haven't worked with these buck converter ICs before. How risky is the 2.5MHz switching likely to be? The recommended filter (2.2uH + 22uF) looks like it'll have very low output ripple.

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30 Mar 2015 18:23 #30478 by moss
Replied by moss on topic Single-Board Universal Module
Output ripple is claimed to be 100mV - 220mV (@ Vin 5V ~ 12V) fig. 21
(p-p or rms?)
Should that be a problem, the above suggested extra coil of 2.2uH 0805 and 1uF cap will lower it by 50dB.
The only way to know is to test it.
Getting rid of 1W of heat on that small PCB should be a bonus for temp sensitive stuff, oscillators etc, besides perhaps doubling battery life?

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30 Mar 2015 19:37 #30480 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
where do you see that? It looks more like 10 to 20mV to me from Fig21. The datasheet already specifies an LC filter. You would add a 2nd filter in series with the spec filter to further reduce noise (if needed)?

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