COMPLETED.. VMusic2 / BS2P40 Temperature data logger for Polar Bear Plunge in T

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So, I am doing the Polar Bear Plunge at South Lake Tahoe to raise money for Special Olympics of Northern California this Saturday, 3/21, and I got thinking that it would be cool to make a waterproof temperature datalogger to wear for the plunge. I need some help because I only have the Sensirion Temp sensors which cannot be submerged and the only USB drive device I have is the Vmusic2.

Anyone have any experience using the VMusic2 as a regular datalogger?
Any suggestions for a temp sensor that I can attach to my ankle, thigh, or waist?
It needs have a quick response and be waterproof.
Anyone in the Sacramento/Roseville area that can loan me the needed devices?
Suggestions for waterproofing the BS2? (plan is using a waterproof digital camera case or lure case from walmart)

thanks!


for more info about the plunge, go here:
http://forums.parallaxinc.com/www.kintera.org/faf/donorReg/donorPledge.asp?ievent=294439&supId=242419345
the page uses java, so it loads a little slow.

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Andrew Williams
WBA Consulting
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Post Edited (WBA Consulting) : 3/25/2009 3:58:15 PM GMT

SRLM

Probably a better sensor would be something like a temperature probe or this. With the last, you can cover everything except the plastic tip with conformative coating or a box, and leave the plastic to the air/water.

If you have to use the sensiron, you can cover the whole module except the temperature sensor with conformative coating, and the temperature sensor with metal spray paint. It might permanently ruin the humidity sensor, though.

sylvie369

One of these might do it as well:

http://www.vernier.com/probes/tmp-bta.html

perhaps with one of these to connect it to your recording device:

http://www.vernier.com/accessories/access.html?bta-elv&btd-elv&template=basic.html

I've used the analog protoboard connector to connect Vernier probes to Stamp and Propeller modules. It works just fine.

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Well, I just scored a used liquid temperature probe from a friend. It's a 10k, 25C, Z curve type in a brass housing. The response time is fairly decent and should work. It's sealed with a length of glue-shrink off the back, so it should be waterproof "enough" for my needs. It was pulled from a PVC tee fitting from a medical device.

I think I may still try to seal a Sensirion as SRLM suggests. I have plenty of those to play with and plenty of code. Also, I have one of the SF1 caps and took another look at the spec sheet. I found that, when sealed and epoxied to the PCB properly, the cap will provide IP67 protection. (up to 1 meter submersion)

Next steps:

Start looking for code examples with a Z curve thermistor and a BS2.
Start looking into using the VMusic2 as a USB datalogger.

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Andrew Williams
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steve_b

Polar Bear Plunge in Tahoe?? You should come to Canada for a proper Plunge!! Here we have to rassle d'er bears to get at the hole! [noparse];)[/noparse]

If it is an actual "plunge"...meaning you'll be getting out faster than you got in, your sensor might not acclimatize fast enough.
Why not just get an old LM35 temp sensor and heat shrink it. Walk up to the hole with the sensor taped to the end of a pole and dunk it in.....

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<FONT>Steve



What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!

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I received a stainless steel probe today from QTI. I think it is going to work out very nicely. Due to time constraints, I am just going to have the data logger record the resistance measurements and I'll load the data into excel for the temperature conversion. I don't have time to figure out the code for the curve calculations.

steve_b The response time was a main concern, but I do plan on giving the sensor at least 10 seconds. The two probes I have are pretty responsive. I took this QTI sensor at room temp (10.86Kohm = 71.6F/22C) and dropped it in a cup of icewater. It settled at 27Kohm (36.5F/2.5C) in 13 seconds. It took about 10 minutes to get back to room temp.

I found this thread for vmusic code as a datalogger:
http://forums.parallax.com/showthread.php?p=678818

However, I found this code of a BS2/SD datalogger and that will reduce the overall size. I have all the parts, so that looks enticing.
forum.sparkfun.com/viewtopic.php?t=11295&highlight=sensirion+diptrace

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Andrew Williams
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After loading up my VMusic2 with the latest firmware and ruling out an incompatible USB drive, my setup works great. However, I must be missing something obvious with RCTime and the math. I am using a BS2P40, 10k thermistor, 0.1uf cap, in the state 1 setup. My RCTime values in the living room are ~1740. How do I work that back into a resistance of ~10k? My code thus far is attached along with the output file from dunking the thermistor in a cup of ice water (abrupt change at the 41st reading).

I will be trying the conformal coating and SF1 cap on the sensirion tomorrow.

I think I have also come up with a solution for the case by rigging up a socket for the BS2P40 with all the other parts.

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Andrew Williams
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Well, the proto version of my datalogger is done. It now has a Sensirion SHT11 attached and is logging both the thermistor value and the temp from the SHT11. I ran out of variable space so I can't do the humidity. I already did some variable recycling, so I can probably squeeze a little more if I wanted humidity, but since I only care about temp (humidity should be 100% underwater), I didn't bother spending more time.

I coated the SHT11 module and SF1 filter cap with Dow Corning conformal coat and it looks pretty good. Still works so far. I am going to do another coat before I give it the dunk test.

I added a status LED so I will be able to see that data is being logged without having to check the USB stick.

I modified the VMusic2 module with a 2nd USB connector on extensions so I can reposition the USB stick to save enclosure real estate. After all of that work, I found my PQI memory stick which is about the size of a USB connector. Oh well.

Latest code and pictures attached. Excuse the mess.....

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Andrew Williams
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Here is the code (BS2P40) and some pics.

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Andrew Williams
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Now that I am starting to piece things together for the case, I came across a question. My plan is to solder wires, etc, directly to a 40 pin socket. That should be simple enough, but what about power considerations???

Here's me question: What's the best way to power this setup with minimal components?
1) 9 volt battery with 7805 feeding 5 volts to the BS2P40, SHT11, VMusic2 individually?
2) 9 volt battery feeding the BS2P40 and running the VMusic2 and SHT11 off of VDD from the BS2P40?
3) Power the SHT11 using an IO pin?

A) VMusic2 datasheet states a "5 volt supply" but everything is dropped to 3.3 except the USB stick. Unknown current draw.
SHT11 can function from 2.4 to 5.5 volts and draws less than 5mA.
C) BS2P40 spec is 5.5-12 volts for Vin or 5 for VDD. Draw

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Andrew Williams
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Tracy Allen

Have "fun" on the plunge tomorrow, especially given the oncoming weather. Also measure the temperature of the hot cocoa, mulled apple cider, or better yet, Irish coffee that you get when you emerge from the lake! I saw a news item the other day about people who are training for a marathon around the North pole.

I think your option number 1 is the best bet. The VMusic2+flash drive is going to draw upwards of 150 mA or more when active. Some brands of flash drive draw more than others. It is too big a demand on the Stamp's internal regulator. Use an ample filter capacitor.

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Tracy Allen
www.emesystems.com

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Tracy, thanks for your response. I went with option one and used an LM7805.

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Andrew Williams
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Plunge went great, had a blast, wasn't as much of a cold shock as I expected. Was in for about 3 minutes, down to my neck. The hardest part was trying to walk. The icy water stiffens your legs like crazy. Little bit of snow flurry on the way home, made for a beautiful ride.

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FINAL PROJECT RESULTS:

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Good news: My "portable" version setup worked perfectly with my program and I only had one assembly error.

Bad news: Short answer, "worked perfectly with the wrong program".

I actually wasn't able to work on it Friday night because we were with family til late, so I gave up on taking the logger since it wasn't "made" . However, my wife (gotta love her) made sure I had time in the morning. I finished my setup just before heading to Tahoe and it seemed to work. Logger LED functioned correctly during the plunge, another plus. No water made it into the 3 layers of ziploc bags.

Got home, plugged in the USB stick and no file.....well, just the old file named THERM.txt, no "PLUNGE.txt" which is what my latest version creates. I let the program run at home again, status LED was fine, plugged in the USB stick, only the therm.txt. I deleted the therm.txt file so the drive was blank, tried again.... just the therm.txt file; Hey, wait, I thought I deleted that......insert light bulb here......(the old PEBKAC error)

When I reprogrammed the stamp for 1200 samples instead of 10 samples, I used the older version "plungelogger.bsp" that only read the thermistor (instead of "plungeloggerSHT.bsp") and saved the file as therm.txt. So I did have thermistor data from the jump, until I deleted it during my debugging.
The USB stick is quarantined until I confirm the data is unrecoverable. I am running some low level disk tools on it now.

overall, had a blast, can't wait til next year. Pictures of setup are attached. (a little messy, but I did it from scratch in 35 minutes)

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Andrew Williams
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I was able to recover the file from the plunge. Unfortunately, only the first 11 readings are usable and read around 51 degrees which was outside temp. So I never got any "underwater" readings. Lessons learned for next year. I did dunk the SHT11 into water for 10 minutes and it read just fine so the conformal coating and SF1 cap are doing their jobs. Since this was my only current SF1 cap, I will be adding a grommet and Molex SL connector so it can be re-used easily.

I came across a few other things as well and I will be creating a new thread for those to be answered.

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Andrew Williams
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