Propeller Based, Stamp-Compatible, uSD Datalogger Module

WBA Consulting

While beginning my plans for making a small datalogger for next years Polar Bear Plunge, I started playing around in DipTrace to actually make a PCB for one to be on my "completed projects" shelf. I haven't done a lot of deep thinking yet, but the PCB is taking shape as a very small form factor Serial uSD datalogger that also has 8 IO pins accessible for additional sensors, inputs, etc for logging and/or controlling via the 3 pin header (Serial, VDD, GND) or directly by the propeller. (As I typed out the three pin names, I realized the 3.3v/5v shift may need to be part of my deep thinking). Attached is my brainstorming layout, any feedback? Some thoughts:

1) The 3 pin header would be used as a connection to program the module to function similar to Bean's SX SD datalogger module.
2) The 4 pin header is a standard programming header.
3) The row of 10 SMD pads on the back is for VDD, P0-P8, and GND. This allows a standard 10 pin header/socket strip to be soldered on its side to make a mini-prop SIP module or give access to additional I/O.
4) The uSD socket on the back will probably change, but is now a push-pull, minimum footprint style from Molex. The uSD card hangs more than halfway out of it.
5) The space on either side of the uSD would be for the SD pullups and an LDO
6) Yes, a lot of I/O pins will go unused, but for a multi purpose micro module, that's a justifiable sacrifice. The only other option is to go to a non-standard header (like 2mm) to fit more since the concept is to be minimal size.


Questions:
1) As a standalone datalogger setup with an SHT11 attached to the available IO pins, what other things should I need to be taking into consideration?
2) What's the best way to make this compatible with 5 volt devices? (basic stamp, etc)
3) What's missing from my circuit?
4) What don't I need on the board?
5) Am I heading in the wrong direction for a small uSD Datalooger module?
6) What should I be looking at for a streamlined, simple SD logger program?

All manners of feedback is welcome: positive, negative, ridicule, etc

thanks!

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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
Special Olympics Polar Bear Plunge, Mar 20, 2010

Mike Green

How about bypass capacitors for Vdd / Vss? How about pullups for the I2C lines? How about identifying what's what? I can guess what might be the Propeller and what's likely to be the EEPROM, but what's the crystal? Is that U2?

There's a nice line of signal level devices made by TI including a bidirectional 3.3V to 5V level converter that comes in multiple channels. You might consider that. I think it's used in the new Propeller-based Parallax Servo Controller. You might look at the documentation for that.

WBA Consulting

Mike, thanks for pointing out the flaws in my haste to post this.....

I didn't place the obvious passives that would be put down in the final layout. I was hoping to get some feedback before I got tunnel vision in my design. Bypass caps, pullups for I2C and SD. Here's a list of what's what:

U1: P8X32-M44
U2: 5MHZ Crystal (package style will likely be changed)
U3: 64k EEPROM
C1: 10uF cap on 3.3v
D1: Protection diode
J1: Propclip/plug header
J2: 3 pin serial I/O and power header
(J3): uSD socket (no reference shown as I just threw together a pad layout for a socket I have)
(J4): 10 SMD Pads for I/O expansion

This layout was thrown together in a few minutes while brainstorming, so I apologize for it's crudeness.

I will be looking at some level shifting ICs. I also have some good level shifting circuits that are really simple from "The Microcontroller Application Cookbook" I may try something along those lines because real estate will be less of an issue and I really only need level shifting on board for the Serial IO.

I am also thinking of moving the uSD off the module by making use of Parallax's new uSD Card module. It's small enough to be used as a piggyback board. If I lengthen the PCB to 2", it will work well.

thanks

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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
Special Olympics Polar Bear Plunge, Mar 20, 2010

dMajo

What about replacing the eeprom with a ramtron FM31L278 device: you will have the same boot-eeprom capability (32K-unlimited writes) plus a RTC. Perhaps someone wish to timestamp the logged events/data? The counter inputs can be placed nerby the IO pads, the watchdog can be used to reset a non responding/hanged prop.

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· Propeller Object Exchange (last Publications / Updates)

WBA Consulting

dMajo, I will look at the FRAM, especially since RTC would be a nice addition.

In the meantime, I took a different stab at this idea. Attached is a another brainstorming layout. It's a basic Prop circuit crammed onto a small PCB but with 0.1" headers for the I/O access. The uSD socket is dumped and one set of header pins will be a direct pin-pin match for the Parallax uSD socket module. The second row of header pins would be for I/O access as before. The back of the PCB is currently empty, leaving real estate for level shifting circuitry. Again, still just brainstorming, but would still like to end up with a clean and multi-functional mini-prop design.

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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
Special Olympics Polar Bear Plunge, Mar 20, 2010

Post Edited (WBA Consulting) : 9/24/2009 6:53:37 AM GMT

mctrivia

you will not have space for stuff on bottom with that layout unless using 4 layer pcb. you need to consider space for the traces.

you could use my propmod-us_sd has uSD on board already and headers can be directly soldered to your WBA-TH1M

as you mentioned sandwitching my propmod-1x1 would give very small footprint but does require an addapter board to fit.

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propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

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WBA Consulting

For 8 channels of level shifting, you are right. But for 2 or 4 channels, there's plenty of room. One channel for the Serial I/O to make it stamp compatible and 1 (or 3) for some of the prop I/O pins. By limiting the number of channels, I can use a VSSOP8 (TI TXB0102) or SOIC-14 (TXB0104) package for the level shifting IC. I even thought of using a single channel SOT23-6 for the Serial I/O, but I figure it would be nice to have some ability of using 5 volt sensors, etc.

I am definitely looking at your Propmodules to leverage for this idea. It might be a better idea to make a backpack for an existing product. If I mount Parallax's uSD module to the top of the PropModule 1x1 and make a small level shifter PCB for the bottom, then my original idea is accomplished. Back to the brainstorming board.

thanks for the insight!!!

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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
Special Olympics Polar Bear Plunge, Mar 20, 2010

WBA Consulting

I am making progress with my uSD Datalogger (as seen on this thread). I have been thinking a lot about a module design that will benefit more uses than my plunge. Here are my three thought paths currently, all of which would be open source designs and will allow use with Basic Stamps:

1) Continue with a micro sized datalogger PCB as started in this thread.

2) Create a backpack board for the 1x1 propmodule or the PropstickUSB that adds appropriate features to accomplish my goal as stated in the subject line.

3) Create a small PCB that's a little more versatile and user friendly by increasing the size and utilizing the TQFP package rather than the QFN and matching the size of a 2 (or 3?) AA battery pack.

Anyone have any feedback on these three ideas?

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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
Special Olympics Polar Bear Plunge, Mar 20, 2010