How many Temp Probes to an Arduino

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How many Temp Probes to an Arduino

Post by sumer »

Hello all,

I am new in the arduino world and am learning some programming.

Can someone please tell me how many teaperature probes (https://www.adafruit.com/product/381) can be attached to an Arduino (Mega or Uno)?

Thanks.

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Re: How many Temp Probes to an Arduino

Post by adafruit_support_bill »

In theory, 18446744073709551616. But I don't think we have that many in stock. ;)

Seriously, each device has a unique 64-bit address. The one-wire protocol will support any number of them on the one-wire bus.
In practice memory, electrical considerations, budget, product availability, performance and sanity would all prevent you from approaching that 2^64 sensor limit.

Depending on what you want to do with them, Arduino memory or performance would probably be the limits you run into first. What is your application? How many sensors do you need and how fast do you need to sample them?

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Re: How many Temp Probes to an Arduino

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adafruit_support_bill wrote:In theory, 18446744073709551616. But I don't think we have that many in stock. ;)

Seriously, each device has a unique 64-bit address. The one-wire protocol will support any number of them on the one-wire bus.
In practice memory, electrical considerations, budget, product availability, performance and sanity would all prevent you from approaching that 2^64 sensor limit.

Depending on what you want to do with them, Arduino memory or performance would probably be the limits you run into first. What is your application? How many sensors do you need and how fast do you need to sample them?
Umm.. Okay, So here is what I want them to do.
I have a fishroom with around 100 aquariums. All the aquariums have thermostat heaters in them. I work with fishes which are getting extinct in the wild.
Now, thermostat heater fail sometimes. The thermostat stops working and then the heater boils the water which ultimately kills all the fishes in the tank.
So waht I am trying to do is put one of these sensors in each tank and keep a track of temperature in all the tanks. If temperature in any tank goes above a desired level, it will send me an email (I hope the ethernet shield would let me do this) or maybe a text (if I buy the GSM shield) and I can come down starirs in the fishroom and do something about it.
In the future maybe I will join some relays in the system so that if temperature is going up, it will trap the power and the heater will stop heating.

So this is what I want to do. Initially I will start with, say, 5 aquariums and then will increase if it this experiment succeeds.
So would one Arduino be able to read data from 25 probes (let's say I buy 4 arduinos to cover 100 tanks)?

Thanks,
Sumer.

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Re: How many Temp Probes to an Arduino

Post by adafruit_support_bill »

Even 100 probes should not be much of a problem for an Arduino memory wise. But wiring considerations favor smaller networks. If you have the flexibility to divide it up among several Arduinos, that would be good.

This white-paper has some excellent information regarding one-wire networks.
http://www.maximintegrated.com/en/app-n ... mvp/id/148

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Re: How many Temp Probes to an Arduino

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Wonderful! Thanks a lot.

One more question though: So these probes seem to have three cables. I am guessing one is ground, one is power and one is data which goes in the digital pin port, right?
So, don't we have only like 13 digital ports on UNO?
So I understand that the ground and power cables out of all the probes can be joined and direct to one pin in Arduino but what about all the data pins?
Doesn't it mean we can add only 13 probes to one Uno?

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Re: How many Temp Probes to an Arduino

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All of the data wires share the same Arduino pin. That is why it is call a "One-Wire Bus" The arduino broadcasts the 64 bit address of the sensor it wants to talk to and the corresponding sensor responds.

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Re: How many Temp Probes to an Arduino

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adafruit_support_bill wrote:All of the data wires share the same Arduino pin. That is why it is call a "One-Wire Bus" The arduino broadcasts the 64 bit address of the sensor it wants to talk to and the corresponding sensor responds.
Ohhhh... I see what you mean. So it means that each sensor has a (or would be assigned one by the arduino) 64 bit address. That is amazing.
I need to start experimenting now.
Thank you so very much for explaining these things to me. I really appreciate your time.

Thanks,
Sumer.

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Re: How many Temp Probes to an Arduino

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So it means that each sensor has a (or would be assigned one by the arduino) 64 bit address.
The address is assigned by the manufacturer. At startup, the Arduino queries to find out how many sensors are out there and makes a list of addresses for the ones that respond.

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Re: How many Temp Probes to an Arduino

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adafruit_support_bill wrote:
So it means that each sensor has a (or would be assigned one by the arduino) 64 bit address.
The address is assigned by the manufacturer. At startup, the Arduino queries to find out how many sensors are out there and makes a list of addresses for the ones that respond.
Wow. That is so interesting and fascinating. I never thought of it that way.
Thanks a lot.

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