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Topic: DS18B20 multiple sensors (Read 8 times) previous topic - next topic

afremont



At some point, it will stop working again.  If you have an oscilloscope, you can see how the signal degrades as you pile on sensors.  It's not like it's a very clean signal to start with.  Long cables will add to your woes because of the capacitance of the wiring.  Lower value pull-up resistors will help in many situations.  As you already saw, you could go as low as 1k if needed since it was working until you got it below about 500 ohms.  The sensors were only designed to sink 4mA which means even 1k is a little small.


You're beyond me but could he use a circuit to drive a led as a line indicator?

Also, couldn't an Arduino support more than one 1-wire bus?



I'm not sure what you mean about the LED.  Do you mean as an indicator of activity? 

Any pin could be another 1-wire bus, but I don't know if the library supports that or not.
Experience, it's what you get when you were expecting something else.

GoForSmoke


I'm not sure what you mean about the LED.  Do you mean as an indicator of activity?


Perhaps a difference in brightness would tell something useful about the power line (non-parasite) with X number sensors connected? It would vary as signals are sent but would anyone be able to see that as anything but light level?
If it could then he could tune his power line resistance with a pot.  

Quote
Any pin could be another 1-wire bus, but I don't know if the library supports that or not.


If DS got the idea that they could sell more devices by supporting more pins, would it happen ASAP?

I find it harder to express logic in English than in Code.
Sometimes an example says more than many times as many words.

gasperinn

#22
Mar 02, 2013, 12:00 am Last Edit: Mar 02, 2013, 12:02 am by gasperinn Reason: 1
Reporting :) Successfuly connected 22 DS18B20 sensors and one DHT22. I used one 4.7k resistor for those 22 DS18B20 sensors and one 4.7k resistor for that one DHT22.

DHT22 sensor is wired like that:
http://api.ning.com/files/PKFE7DukclQO*V1lbgx2A1Xd*8ffMCvXqAA4Qd-*7J2cFd9DkoZyqDjdIURURatYsNTYNDLc77VSqOklXk-YnQmKI4l6dfie/RHT03arduino1.png

How can i wire multiple DHT22 sensors on Arduino Mega board? Becouse DHT22 data cable has to be each on its own pin, so therefore i have to use as many resistors as there are DHT22 sensors or is there any other way to wire it up? Becouse if that is so, i think there i'll have the same problem as i had with DS18B20 sensors.

GoForSmoke

There are parallel to serial shift registers. You can read a whole line of bits from the pins on chained shift registers (1 CS on the master to CS chip 1 chains to CS chip 2, etc) as SPI serial at 2 MHz. But, hardware SPI may use pins that 1-wire does so maybe use soft-SPI and 1 MHz speed.




I find it harder to express logic in English than in Code.
Sometimes an example says more than many times as many words.

afremont


There are parallel to serial shift registers. You can read a whole line of bits from the pins on chained shift registers (1 CS on the master to CS chip 1 chains to CS chip 2, etc) as SPI serial at 2 MHz. But, hardware SPI may use pins that 1-wire does so maybe use soft-SPI and 1 MHz speed.


The 1-wire stuff is only in software already, so you can pick any pin you want for it.

(gasperinn)   That's cool on the 22 connected.  How long is the bus physically?
Experience, it's what you get when you were expecting something else.

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