Hi Tony, I was hoping someone would recognize one of the thermistors at the link I sent with 4 possibilities. Unfortunately they don't have specs on them so I really can't tell which would work best... if at all. Maybe I should just go to "Plan B" and order LM35Ds from a supplier in TX and get the usb cables for power supply like the XO explosion kits have (like the one Mike Lee has). The cost would only be about $3.00 more. Any ideas from the rest of you??? I will get the light sensors for sure. I guess I will also have to figure out which 680 ohm resistor to get out of 19 available from the place in TX http://www.alliedelec.com/search/searchresults.aspx?dsNav=Ntk:Primary%7c680+ohm+series+resistor%7c3%7c,Ny:False,Ro:0&dsDimensionSearch=D:680+ohm+series+resistor,Dxm:All,Dxp:3&SearchType=0&ps=60&fromsearch=true&term=680+ohm+series+resistorThe store here is out of them. Anyone that can look at the links in the original email and this one and clue me in to what to get a bunch of us will be very grateful when we make and play with our sensors in SF! Thanks,Caryl
> To: [email protected] > CC: [email protected]; [email protected]; [email protected] > From: [email protected] > Date: Mon, 15 Oct 2012 14:51:29 +1100 > Subject: Re: [support-gang] Sensor Experts: I need help with my shopping list! > > Caryl > > > Temperature (thermister). Which of these will work best? > > www.allelectronics.com/make-a-store/category/770/Thermistors/1.html > > You want the resistance at 20C, 70F to be very roughly mid way (in terms of > voltage) in the measurement range of the XO. This gives the best range and > accuracy. > > http://wiki.sugarlabs.org/go/Activities/TurtleArt/Using_Turtle_Art_Sensors#Measuring_Temperature > > has a thermistor which is 5000 ohms at 20C which is somewhere near mid range > for an XO-1 (I dont remember exactly what mid range is but you can calculate > it looking at the source code, 10kohm sticks in my memory but...). The XO-1.5 > has a much better measurement range so choose on the basis of the XO-1 > > whether it is best to use positive or negative temperature coefficient, my > choice of NTC was pretty much random. It might have had a difference on how > simple the calibration function was but I didnt give this much thought > > > Light Will this one work? > > http://www.allelectronics.com/make-a-store/item/PRE-24/CdS-PHOTOCELL-PHOTORESISTOR/1.html > > Yes, looks OK, mid range light is within the XO's range > > > There isn't a lot of info about the ones for measuring soil moisture (but > > there is interest in this one), water salinity, and the lemon battery > > (looks like a fun one). They must all use the 3.5mm plug, right? Can one > > sensor be made to use for all of these or do they need different components > > in the circuit? If so, what different things are needed? Would we need to > > insert a resistor for XO-1s with the lemon battery? > > > > How about wire? Other than copper wire for the water salinity, what should > > I try to get for the rest? Gauge? Material, bare or covered? > > Whenever you are terminating the plug with bare wires you should include a > 680ohm series resistor to protect the XO-1 > http://wiki.sugarlabs.org/go/Activities/TurtleArt/Using_Turtle_Art_Sensors#Specifications > > When measuring moisture/salinity just experiment with 2 bits of copper wire > from your junkbox. The length of wire you use can be determined by trial and > error so they are mid measurement range. The measurements are uncalibrated, > what matters is the relative measurements. > > The lemon battery can use one of the copper wires above and any galvanised > nail > > > For the plugs, can we get cords with one plug at each end, split them and > > use for 2 sensors? Something like these? If we do that what other wire will > > I need to get? > > http://www.allelectronics.com/make-a-store/item/CB-389/12-CABLE-3.5-MM-STEREO-PLUGS-BOTH-ENDS/1.html > > Yes, its a 3.5mm stereo phono plug. I have used bare plugs and soldered my > leads. Some premade leads have a foil rather than a wire for ground that may > be difficult to connect to. Note the previous warning about the series > protection resistor for the XO-1. > > Tony
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