I've set up 5 temperature probes for my home brew pub, but when adding number 5, one wire address finder or my program can't find the last one. If i connect it alone or as no. 4 it works. I've got a tip that it might need external power, so I added a 7.5 Volt 1000 mill Amp power source. 4 probes are connected to one wire which measures the temperature tap tower, one half way up in the pipe where the beer lines go, and 2 probes to measure temp in the fridge where I have the kegs. All these 4 mostly works fine. (Sometimes I get error readings)
Probe 5 is a separate wire from the arduino card. When the other 4 is connected no. 5 does not connect.
I've also tried to connect a separate power sources to probe 5 only connecting the blue wire to the Arduino card. This was 6 Volt and 300mill Amp. The wire is about 10 meters
Is there any limitation to how many probes that can be connected to the card? Is there any guideline to how strong external power supply’s has to be when lines are long?
i'm fairly new to this and when you mention parasite power, i guess you mean addtional power from external source( not connected to Arduino)
I've tried both separate power to probe 5, only connecting the blue wire to Arduino, and also using all wires using power from the Arduino Card. Same result no contact with probe 5. The other 4 probes has no external power.
No, I don't mean external power not from the Arduino (the Arduino is easily capable of supplying all the power that your 5 sensors need). What I mean is, do you have the Vdd pin of each DS18B20 connected to Arduino +5V, or have you left the Vdd pins unconnected?
You may need to reduce the value of the pullup resistor. Try 2.2K. The minimum you can use is about 1K.
percbakk:
If i connect it alone or as no. 4 it works.
When you do that, are you using the full 10m, or are you using some temporary short cable lashup?
I believe you need quality cable with DS18B20s. The problems I have had like that have been down to extending the sore-bought cable with 3m of cheapo multi-conductor.
percbakk:
i'm fairly new to this and when you mention parasite power, i guess you mean addtional power from external source( not connected to Arduino)
I've tried both separate power to probe 5, only connecting the blue wire to Arduino, and also using all wires using power from the Arduino Card. Same result no contact with probe 5. The other 4 probes has no external power.
The resistor is 4,7 kohm.
You have two methods of using the D18B20 (well technically 3)
You provide no power at all to them and they draw their power through the Data line - unless you have a serious issue with available numbers of wires i would strongly suggest (especially as a NOOB) that you do not do it this with to begin with
As you will see on the sensor there are 3 pins - one of these is ground, one is data and one +ve. If you drive these from the Arduino then you are providing power to the sensor from the Arduino - you need to put a resistor across the +ve and data lines in this mode - this is a bit of a trial and error thing - a good starting point is a 4k7 - but it will depend on the quality of your wires, their length and the number of joins.
Now as a variation on each of these you can daisy chain or star your sensors - i.e. all of the sensors connect to the same data pin on the arduino - alternatively you have the data line of each sensor connect to a different digital input on the arduino - unless you are incredibly tight for pins i would recommend starting with each sensor on its own data pin and with a powered setup using 3 wires as in #2 above.
If you get all sensors working and returning meaningful results then you can start connecting more than one sensor to a pin (if you wish) - personally i prefer to stay away from this method
I've tested probe no. 5 with full length alone and then it works fine. I've also tried it in full length with 2 and 3 other probes and that also works fine. It seems to be some kind of limit when connecting no 5. (There is also some instability when using a total of 4, but I do get contact with all with address finder.)
I've attached a picture of how it's set up.
I've tried to change to other resistors, but then it does not work at all. I currently using 4K7. I've tried 2,2 and 1K, I think. The set I got from Deal extreme was so poorly marked by bad blurry handwriting so I'm not 100% sure.
I'm using the traditional old telephone copper wires.
I don't know if there is anything in the datasheet about this. I guess it's something you are supposed to know. My cables are shielded but there is nothing special about them and I guess cheap shielded stereo audio would be fine. My dud extension cable was only temporary and I moved the meter rather than fix the cable.
and why is the cabel not the problem when using 4 probes?
I don't know. Your pullup might have something to do with it. Maybe luck only just got you to three.
As you are powering the Vdd pins of the DS18B20 from +5V, there should be no problem with using a 2.2K pullup resistor. I suggest you invest in a multimeter (even a cheap one is better than nothing) so that you can measure those resistors. The more cable length you have, the greater the capacitance and the more likely it is that you will need to use a smaller pullup resistor.
Alternatively, limit yourself to no more than 3 sensors per Arduino data pin.
IMO telephone cable should be OK unless there is a lot of electrical noise in the environment.
You might just be getting signal reflections. Insert a 220 ohm resistor in series to each of your 2 red wires at the point where they connect to the Arduino. That, theoretically, should eliminate the reflections.
A note on parastic powering: if you are not supplying 5V to the DS18B20, connect the VDD pin of them to Ground (yes, ground). This is recommended practice from Dallas/Maxim - "VDD must be grounded for operation in parasite power mode."
dc42:
As you are powering the Vdd pins of the DS18B20 from +5V, there should be no problem with using a 2.2K pullup resistor. I suggest you invest in a multimeter (even a cheap one is better than nothing) so that you can measure those resistors. The more cable length you have, the greater the capacitance and the more likely it is that you will need to use a smaller pullup resistor.
Alternatively, limit yourself to no more than 3 sensors per Arduino data pin.
IMO telephone cable should be OK unless there is a lot of electrical noise in the environment.
Hi Again!
With a 2.2K pullup resistor it worked. I've now tested with not just 5 but 8 probes, and it works great!
