Scorpion Controller Board

Project to send a balloon into lower space with payload
Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Scorpion Controller Board

Post by Rris » Tue 07 Dec 07 2010 12:20 am

My controller board with have a NXP LPC2388 ARM 7 at it's core. It will be shielded by:
903-1054-1-ND BOARD SHIELD 1.0X1.5" FRAME with
903-1017-ND BOARD SHIELD 1.0X1.5" COVER over it.

The processor will run the TinyCLR .Net Micro Framework Port. It will have a uSD connector for logging and possibly a USB host port to plug a Corsair Dominator into for backup logging. Those things are meant to be indestructible.

It will have an onboard SkyTraq Venus 63x chip (hoping for 638 due to extra RF grounding).

The Venus chip has an RF shield over it also. RF Input will be through a SMA connector.

The PCB will have a XT60 connector from HobbyCity for the battery to connect in directly, with no cables. There will be two switch mode power supplies, one for 5v, one for 3.3v. The 3.3v will have to be much more substantial than then 5v due to most sensors, the 1W 900mhz transmitter and gps all being 3.3v devices.

A ribbon cable will be used to connect to the sensor board, or possibly some shielded USB cable (simply for the shielding) or some sort of military spec/low temp spec cable assembly.

There will be LEDs for power status (one on each rail), GPS status (from GPS) TXD/RXD for the Aerocomm module and a "working" status LED for the NetMF app.

The PCB will also have a temperature sensor or two integrated into it to monitor the board temperature.

There will be FET's for controlling less critical sensors - such as the geiger counter - that will allow them to be powered down if the battery is depleting faster than anticipated. They could also be powered down on the descent if voltage is lower than expected at the peak (since we've already logged the air column on the way up).

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: Scorpion Controller Board

Post by Rris » Tue 07 Dec 07 2010 12:27 am

Balloon PCB Day 1:
Created objects for the RF shields - attached is excel spreadsheet that helps figure out the commands for positioning the elements of the footprint.
Created basic schematic for the LPC2388, uSD and USB client port.
Created basic Venus 634 schematic and shielding/gps area basic layout.
ScorpionPCBDay1.jpg
layout after day 1
ScorpionPCBDay1.jpg (63.09 KiB) Viewed 6862 times
Attachments
RFShieldLandHelper.xls
Helper file to work out the eagle commands for RF shield layouts.
(32 KiB) Downloaded 375 times

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: Scorpion Controller Board

Post by Rris » Tue 07 Dec 07 2010 8:35 pm

Tarryn over tonight, so not much progress. Created Venux638 symbol, LBGA69 footprint, and 638 package in Venus library.

GPS is connected to TXD0/RXD0
LED1 is on PWM4 to GND
LED2 is on GPS LED/PIN7
LED3V3 is on 3v3

Added USB host connector.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: Scorpion Controller Board

Post by Rris » Wed 08 Dec 08 2010 12:11 am

Added footprint for the XT60 connector. It has a protection diode just in case and a 15uf filter cap on it.
Battery voltage goes to ADC0.

Switched the silly HC-49US SMT format crystal that was on the board (silly GHI) out to a 5x3mm SMT. I'd go smaller but there is heaps of room in the RF shield at the moment.

Tomorrow i need to add powersupplies.

Board is layed out as basic blocks at this point.
ScorpionPCBDay2.jpg
day 2's progress
ScorpionPCBDay2.jpg (61.7 KiB) Viewed 6859 times

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: Scorpion Controller Board

Post by Rris » Wed 08 Dec 08 2010 12:17 pm

So i've worked out the power draw i'll require.

3.3V 1485mA
5V 1050mA

Based on:

Code: Select all

Device	Voltage	mA Draw	Milliwatts
VideoTX 500mw 2.4ghz	5	450	2250
Aerocomm 1W (100% TX time)	3.3	1300	4290
Geiger Counter	5	30	150
NXP2388 ARM7	3.3	110	363
MicroSD	3.3	20	66
Other Sensors	3.3	10	33
GPS	3.3	35	115.5
GoPro HD Cam	5	400	2000
USB Memory	5	20	100
LEDs	3.3	10	33
Methane CNG Gas	5	150	750
This doesnt include Daniel's transmitter or his processors/gps. This is purely for my sensors/logging/processors (and the video system).


I have a bunch of LM2596 Switchmode IC's at home which i'll use. They are 3A adjustable switchmode.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: Scorpion Controller Board

Post by Rris » Wed 08 Dec 08 2010 4:24 pm

Finish reading http://www.national.com/an/AN/AN-1229.pdf - very interesting read.

According to WEBENCH designer, maximum efficiency i could hope for is about 81.76%. However with parts i have on hand i'll only get 79.82% @ almost empty on the battery, or 78.64% at full charge on a 6s battery.

At -30c, with no airflow - the switchmode running at max voltage, 1.46A @ 3.3v the chip will be around -18c with the diode heating the PCB up to -5C. A RF shield over the top of the power supplies could allow them to heat the area up more ensuring the switcher IC's stay nice and warm.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: Scorpion Controller Board

Post by Rris » Wed 08 Dec 08 2010 8:49 pm

Powersupplies added. Schematics reated with National's WEBENCH specific to each voltage output based on a 6s lipo input. I changed the diodes to MBRS340T3G's that i have on stock (much less heat with them) and change the inductors to shielded, as well as changing the electrolytics on the 5v to 7343 tantals (all recommended through the webench interface).

Each psu should be about 76-78% efficient, and have a 41mv p-p ripple voltage.

I was hoping to use the same shield as the MCU's but it isnt high enough (6mm, inductors are 7.8mm high when mounted). Need to find alternate RF shields. They may not be required, but they will help keep things warm.
ScorpionPCBDay3.jpg
ScorpionPCBDay3.jpg (88.01 KiB) Viewed 6852 times

Daniel Wee
Site Admin
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Joined: Wed 25 Feb 25 2009 8:00 pm

Re: Scorpion Controller Board

Post by Daniel Wee » Wed 08 Dec 08 2010 10:03 pm

Your board is going to be quite big from the looks of it. Do you have a target size?

Daniel

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: Scorpion Controller Board

Post by Rris » Wed 08 Dec 08 2010 10:24 pm

this is just me laying out sections at a time, not the final design. I'm working on the schematic first and foremost and then putting the bits together onto the PCB. In the past we've done the whole schematic then it's a pain to find all the bits that go together - so i thought i'd work on a "block" then layout those pieces together.

99% of that white space will go away if i can get it to route. It will be as small as i possibly can make it.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: Scorpion Controller Board

Post by Rris » Wed 08 Dec 08 2010 11:43 pm

It all squishes down to a 86x68mm PCB. If i didnt have 3A power supplies on board, it could be smaller (81x43mm). Size doesnt really matter at this point - a 2.4ghz panel antenna we want to have as the base of the enclosure is fairly large!
ScorpionPCBDay3.1.jpg
ScorpionPCBDay3.1.jpg (69.4 KiB) Viewed 6850 times
I still need another voltage divider (for 5v), FET to control the Geiger enable and 1-2 onboard temp sensors.

The back side of the PCB needs the aerocomm header and i may need to put a big drill into the PCB to hold the SMA connector (from MMCX->SMA adapter) unless we mount the SMA directly into the payload enclosure (i'm thinking of getting a laser cut plywood frame made for inside the foam - this would allow everything to be mounted nicely). I also need txd/rxd LED's for the Aerocomm module.

The board also needs connectors to go to the sensor board, and to the video TX for power. The video TX might plug into the board with all it's wires, and the video camera do the same - a nice central plug in point.

I may also add another USB mini-B connector for powering the GoPro camera.

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