djreiswig:
I believe it might be a power issue, but how do I solve it?
I rather suspect something else is going on. DS18b20s run on the smell of an oily rag, and power should not be a problem - unless you are using an inadequate battery, so please don't tell us you are using a 9v PP3. I'm sure people around here have had a dozen on one pin, and you should be able to trawl information on that. Note alo that you can have more than one example of the one-wire function but I believe that that is done as a result of an unwarranted lack of confidence, or simply personal preference, more often than not.
I didn't think it should be a problem. I searched and found someone trying to run 50 on a pin, but never said if it worked. Maybe I need to find an oily rag.
The sensors I have are the ones with the cable attached. I connected the red wires all together to the Arduino 5v+ and the blacks to the -. The yellows all go to the input pin along with a 4.7k resistor with the other end to the 5v+. I think that is correct.
I'm reading the sensors by address and plotting them as a bar graph on an LCD. I'm using the onewire and Dallas libraries.
Just to test the issue, I ran them to a separate Arduino board with the simple code I used to read the addresses one by one. If I connect more than 4 sensors the code can't find any sensors. It will find them if I only hook 4 or less.
Powering off of the USB cable only.
OK, you seem to be doing everything right, as far as the sensors are concerned. You might try leaving the LCD out of the game, and just send serial data to the monitor.
Did that. Different program just to retrieve the addresses. It will only work if I unhook all but 4 sensors. I tried all of the sensors individually and they all work, just not all at once.
My Arduinos are clones, maybe that makes a difference. Not sure why it would, though.
Are you saying to split the sensors up into several groups on different inputs? I was thinking I might have to do that, but I was hoping to run them all off of a single 4 wire cable (using 3 of the wires). If I'm limited to 4 on a wire, I would need 6 wires.
I had not seen that write-up. Unfortunately I don't understand much of what it says.
You haven't told much about the project, probably not enough.
Parasitic or normal power mode?
What value pull-up resistor?
How long are the wires involved?
Some photos of your test setup may also help.
At least in theory a OneWire bus should support lots of sensors, that AN linked in #25 is for long wires (up to hundreds of meters), a different issue. I don't expect you are using that long wires, at least not when testing.
I thought I answered most of that in post #21.
Normal power mode. I have the power wires connected to the Arduino 5v + & -.
4.7k pull up.
For testing I have added about 4 feet of wire between the Arduino and the place where the leads from all of the sensors join. In use, I will probably have 15 or 20 feet of wire.
Not much for a test setup. Just the Arduino, 3 jumper wires to a mini breadboard, the resistor and the sensors.
The code is what I found online to retrieve the sensor addresses. It just loops through the sensors it finds and prints the addresses to the serial window.
My graphing program has these addresses hard coded and polls the sensors on a timer to update the bars.
It works with 4 sensors as well, but when I hook the 5th one up it suddenly can't see any sensors. Unhook one and the 4 come back.
djreiswig:
For testing I have added about 4 feet of wire between the Arduino and the place where the leads from all of the sensors join. In use, I will probably have 15 or 20 feet of wire.
wvmarle was dead right to query this. With all those sensors, wiring them is a possible source of the problem. I have never used more than four sensors at once, and they are always properly packaged with cable like yours, but I immediately had grief when I extended the cable - by 3m. You can't skimp on the cable. The common way to go is with CAT5. There is a lot of discussion around here on this matter. The sensors are available with 5m cable, perhaps more, and their price probably reflects the cable needed. You may also find that a 2.2k pullup is more appropriate with those lengths.
So with cat5 wire, which wires do I use? I will theoretically only need 3 of the 8 wires. Do the power & ground go on a pair and the data on one of the other wires?
I understand they double up with the surplus conductors to use it all. I have never actually done this. I relocated Arduino instead, and made an Ethernet connection to a WiFi repeater. I already had the shield. Yes, there are several ways to skin this particular cat, not all of which involve cable, and only a few that you will get right first time!.
I swapped out the resistor and now I can get 7 to work through my temporary cable. I'm guessing this means there is a signal issue with the network.
If I were to connect the sensors to several inputs on a separate Arduino and split them into say pairs of threes on different one wire networks, is there a reliable and fast way to connect to a second Arduino located at the LCD display? I have some logic in the program that adjusts the display in response to 3 switches as well as an alarm output so I'd rather not run a gob of wires between them.
It's going in a tractor and the sensors are on the implement so wireless probably isn't going to work.
djreiswig:
I swapped out the resistor and now I can get 7 to work through my temporary cable. I'm guessing this means there is a signal issue with the network.
Very likely
If I were to connect the sensors to several inputs on a separate Arduino and split them into say pairs of threes on different one wire networks,
This is incoherent but, as I said above, you can have multiple instances of one wire facilities. Further, you can run DS18B20 on indvidual pins, without any one-wire stuff.
is there a reliable and fast way to connect to a second Arduino located at the LCD display?
Serial is all you need. A Mega driving an LCD panel could receive from four Pro Minis, each of which carry four DS18B20s.
It's going in a tractor and the sensors are on the implement so wireless probably isn't going to work.
I can't quibble about that, but I'm not sure a tractor is a good enough reason not to consider an ESP8266 network(!)
