<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>Jon,</div><div>am having second thoughts about the optical O2 sensor.</div><div>I was given data that said calibration was needed after a while because of a drift</div><div>caused by temperature fluctuations.</div><div>Although calibration would only need to be done every year or two, I would </div><div>need to write a program for that. And I would need to write a program for</div><div>calibration of galvanic O2 sensors if I went with them. So although the optical</div><div>sensors are factory calibrated, this is not going to be that much of an advantage</div><div>to me. They would also be more difficult to source than the standard sensor.</div><div>The optical sensors only have the 0-25% O2 range but I can't imagine going over</div><div>25%. The optical sensor has better accuracy, as all the information I have seen </div><div>on the galvanic sensors say they have an accuracy of +/- 2% on full scale.</div><div>I wonder what procedures Psubbers take with regards to checking calibration</div><div>of their O2 sensors. I am thinking a best practice would be to leave the hatch</div><div>open before a dive & check that the O2 reading corresponds to the standard</div><div>level of O2 in air.</div><div>Cheers Alan</div><div><br></div><div><br></div><div><br></div><div><br>On 10/08/2019, at 12:33 AM, Alan via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="content-type" content="text/html; charset=utf-8"><div><span></span></div><div><meta http-equiv="content-type" content="text/html; charset=utf-8"><div></div><div>Just heard back from SST sensing (UK) re price & accuracy.</div><div>The price is reasonable at GBP 46.85, per unit, but the freight on 3 to NZ is </div><div>GBP 59., which is expensive considering the size & weight. I will see if they </div><div>can put them on a slower boat! </div><div>Had the below response re accuracy...</div><div><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">Hi Alan,<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><o:p style="background-color: rgba(255, 255, 255, 0);"> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">0-300mbar is the ppO2 range.<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><o:p style="background-color: rgba(255, 255, 255, 0);"> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">2% FS is then +/-6mbar ppO2.<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><o:p style="background-color: rgba(255, 255, 255, 0);"> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">O2% = (ppO2 / total pressure) x 100<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><o:p style="background-color: rgba(255, 255, 255, 0);"> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">So, total pressure varies the accuracy of the sensor.<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><o:p style="background-color: rgba(255, 255, 255, 0);"> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">At atmospheric it would be around +/-0.6 O2%<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><o:p style="background-color: rgba(255, 255, 255, 0);"> </o:p></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">We are currently going the opposite direction for ppm (parts per million). Our intention s to then investigate extended range (%)</span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">Cheers Alan</span></p></div><div><br>On 9/08/2019, at 4:08 PM, Alan via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="content-type" content="text/html; charset=utf-8"><div></div><div>Thanks Jon,</div><div>Some great products there. I had read that I could use a resister & capacitor to</div><div>read analog on the digital pins based on the time it took to charge the capacitor,</div><div>& wasn't too thrilled about going down that path. </div><div>Was tempted to buy all those items straight away but will hold off a bit until I </div><div>buy all my sensors. Knowing that I can rely on these options is great though.</div><div>I have requested clarification on whether the optical sensors accuracy is <2%</div><div>error on the range that it measures (0-25%) or on 0-100% O2. If it's on the latter</div><div>then it's not very good, however it was quite accurate in the video I saw so</div><div>hopefully it's <2% on 0-25%.</div><div>I have also asked if they make a product with a wider measuring range.</div><div>Have two price requests in the pipe line & will give an update when the info</div><div>comes in.</div><div>Cheers Alan</div><div><br></div><div><br></div><div><br>On 9/08/2019, at 1:05 AM, Jon Wallace via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br><br></div><blockquote type="cite"><div><div class="ydpb3648c5cyahoo-style-wrap" style="font-family: times new roman, new york, times, serif; font-size: 16px;"><div></div>
<div dir="ltr" data-setdir="false">Alan, you have a few options.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">You can run Processing language on the Raspberry. The Arduino IDE language is in fact the processing language. Check out <a href="http://processing.org">processing.org</a>. However, you are correct in that the Raspberry is somewhat lacking in communication IO pins and does not have any onboard IO ADC pins. You can get around the IO limitation by using a multiplexer like <span><a href="https://www.sparkfun.com/products/13906" rel="nofollow" target="_blank" class="">https://www.sparkfun.com/products/13906</a> or <span><a href="https://www.sparkfun.com/products/9056" rel="nofollow" target="_blank">https://www.sparkfun.com/products/9056</a>. You can get around the ADC issue by using an external ADC like <span><a href="https://www.adafruit.com/product/1085" rel="nofollow" target="_blank">https://www.adafruit.com/product/1085</a> which will talk to the Raspberry via I2C.</span></span></span></div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Check out Teensy at <span><a href="https://www.pjrc.com/teensy/" rel="nofollow" target="_blank" class="">https://www.pjrc.com/teensy/</a> which are Arduino compatible in terms of software but have much more muscle power and IO than any of the ardunio boards. It also has a teensy footprint. I used Teensy 3.2 for the compass project. You should look at Teensy 3.5 or 3.6. Both have 6 serial IO pins, 3 SPI pins, 3 I2C pins, and gobbs of analog pins. If you use the multiplexers listed above you can expand your IO capacity by factors. The 3.5 is 120mhz and 5v tolerant, the 3.6 is 180mhz but strictly 3.3v. </span><div><br></div><div dir="ltr" data-setdir="false">In terms of the sensor, I considered it but it's only a 25% measurement and has about a 2% error full scale. That still puts it within acceptable use but doesn't provide much overhead on the top end. It is however price compatible with typical gas sensors and has a much longer expected life of 5 years.</div><div><br></div>Maybe I'll buy one anyway just to try it out.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Jon<br><div><br></div><div><br></div><div><br></div></div><div><br></div>
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On Thursday, August 8, 2019, 12:03:54 AM EDT, Alan via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:
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<div><div id="ydp3e4cb400yiv5284929921"><div><div></div><div>Hi Jon,</div><div>I was a bit bamboozled by one products description of code for data transmission</div><div>& thought it would be easier to just have a voltage or an amperage range to</div><div>deal with. I don't need the temperature & pressure data as I have other sensors</div><div>for that. The arduino uno B I have has only one tx rx option; however you prompted</div><div>me to review things & found that the arduino mega has 3 tx rx ports & so would do </div><div>for my 3 sensors. Still considering my options.</div><div>I am looking to use the arduino & raspberry pi but have been going round in circles</div><div>a bit. Was learning to program the arduino, then decided no, I need to use the</div><div>raspberry Pi, so was learning Python for programming that. Now I have found out</div><div>that the raspberry Pi doesn't have any analog pins & has a small maximum</div><div>current draw. </div><div>Is there an alternative to those two that is a bit more robust?</div><div>Alan</div><div> </div><div><br clear="none">On 8/08/2019, at 2:28 PM, Jon Wallace via Personal_Submersibles <<a shape="rect" href="mailto:personal_submersibles@psubs.org" rel="nofollow" target="_blank">personal_submersibles@psubs.org</a>> wrote:<br clear="none"><br clear="none"></div><blockquote type="cite"><div><div class="ydp3e4cb400yiv5284929921ydp3da52231yahoo-style-wrap" style="font-family:times new roman, new york, times, serif;font-size:16px;"><div></div>
<div dir="ltr">CO2 meter has an RS485b analog model. But I'm curious, why use voltage instead of serial?</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Jon</div><div dir="ltr"><br clear="none"></div><div><br clear="none"></div>
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On Wednesday, August 7, 2019, 09:45:45 PM EDT, Alan via Personal_Submersibles <<a shape="rect" href="mailto:personal_submersibles@psubs.org" rel="nofollow" target="_blank">personal_submersibles@psubs.org</a>> wrote:
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<div><div id="ydp3e4cb400yiv5284929921ydpa20c71cbyiv7392378644"><div><div><span></span></div><div>Hi,<div></div><div>I've been reading a bit about the solid state optical oxygen sensors which</div><div>have a longer life & are more reliable than traditional galvanic cel ( battery)</div><div>type O2 sensors. </div><div>Poseidon developed them for the dive industry & they were hailed as a break</div><div>through at the time. There is a company, SST sensing that is marketing them for </div><div>varying applications....<a shape="rect" href="https://www.sstsensing.com/optical-oxygen-sensors-key-benefits-and-applications/" rel="nofollow" target="_blank">https://www.sstsensing.com/optical-oxygen-sensors-key-benefits-and-applications/</a></div><div>Is any one familiar with them? There seems to be a big price difference between</div><div>varying brands.</div><div>The ones I've seen are calibrated internally for pressure & temperature & transmit </div><div>data rather than a voltage or current reading. I am looking for a cheap option that </div><div>has a current or voltage signal rather than data & I will be using something like a raspberry Pi or Arduino to process the reading.</div><div>I am also wanting 3 as in a rebreather to compare readings.</div><div>Do they need much of an O2 flow over them or are they ok just being placed </div><div>randomly within the hull?</div><div>Cheers Alan</div></div><div><image1.jpeg></div></div></div>_______________________________________________<br clear="none">Personal_Submersibles mailing list<br clear="none"><a shape="rect" href="mailto:Personal_Submersibles@psubs.org" rel="nofollow" target="_blank">Personal_Submersibles@psubs.org</a><br clear="none"><a shape="rect" href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" rel="nofollow" target="_blank">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none"></div>
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