Location for MAX31825 #250
Comments
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Sounds interesting, I do not recall seeing this in the datasheet (which page?) |
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See page 13 on attached data sheet |
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Is there an example how to use? bool DallasTemperature::getLocation(const uint8_t* deviceAddress)
{
int b = _wire->reset();
if (b == 0)
return false;
_wire->select(deviceAddress);
_wire->write(DETECTADD);
b = _wire->reset();
return (b == 1);
}Where / how does it read the location ? OK, lets first read the datasheet |
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Yes here is an arduino script running on an arduino mini pro .. but that should not matter. This outputs the temperatures from 5 sensors: I only had one sensor attached here A 10k resistor attached to ADD0 listed as having an address 0x3a :3b ,0 , ,13.94,3a, ,-127.00,3a, ,-127.00,3a, ,-127.00,3a, ,-127.00,3a |
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Datasheet P13 AddressAlthough the 64-bit ROM code allows each 1-Wire device on a bus to be identified for communication purposes, it does
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@pmr1 I would propose something like this int DallasTemperature::getLocation(const uint8_t* deviceAddress)
{
if (_wire->reset() == 0) return -1;
_wire->select(deviceAddress);
_wire->write(DETECTADD); // 0x88
if (_wire->reset() == 0) return -1;
readScratchPad(deviceAddress, ScratchPad);
return ScratchPad[2];
} |
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Should add a test for model in the function #define DS1825MODEL 0x3B // also MAX31825 |
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Ok but the existing api does recognise the 31825 and it does have a get address function so no need ro define an extra constant.
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From: Rob Tillaart ***@***.***>
Sent: Friday, February 9, 2024 12:45:16 PM
To: milesburton/Arduino-Temperature-Control-Library ***@***.***>
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Subject: Re: [milesburton/Arduino-Temperature-Control-Library] Location for MAX31825 (Issue #250)
@pmr1<https://github.com/pmr1>
OK, I understand from the prototype code how one gets a location from the MAX31825.
The implementation has to be engineered, with a more clear API as a DS18B20 does not support this call
I would propose something like this
int DallasTemperature::getLocation(const uint8_t* deviceAddress)
{
if (_wire->reset() == 0) return -1; // not supported
_wire->select(deviceAddress);
_wire->write(DETECTADD);
if (_wire->reset() == 0) return -1;
readScratchPad(deviceAddress, ScratchPad);
return ScratchPad[2];
}
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That model I mentioned is already defined in the .h file (did not invent it) What I do not know if the original DS1825, which has the same model byte as the MAX31825, does support location. Another question is what happens if the 2 lines are not connected / floating? |
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1. No the Max 31825 has a different scratchpad to the DS1825.
2. if Add0, 1 are left connected temperature still reads.
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Subject: Re: [milesburton/Arduino-Temperature-Control-Library] Location for MAX31825 (Issue #250)
That model I mentioned is already defined in the .h file (did not invent it)
What I do not know if the original DS1825, which has the same model byte as the MAX31825, does support location.
Another question is what happens if the 2 lines are not connected / floating?
What does getLocation() return?
Can you test?
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Oh right, I see your point the DS1825 does have an address function but operates via external pins and the address is seen in the configuration register. The Max31825 comes in a solder bump package measuring 0.
8mm x 1mm and is a bugger to solder. So using a resistor is a convenient way of fixing an address.
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From: Rob Tillaart ***@***.***>
Sent: Friday, February 9, 2024 1:01:27 PM
To: milesburton/Arduino-Temperature-Control-Library ***@***.***>
Cc: pmr1 ***@***.***>; Mention ***@***.***>
Subject: Re: [milesburton/Arduino-Temperature-Control-Library] Location for MAX31825 (Issue #250)
That model I mentioned is already defined in the .h file (did not invent it)
What I do not know if the original DS1825, which has the same model byte as the MAX31825, does support location.
Another question is what happens if the 2 lines are not connected / floating?
What does getLocation() return?
Can you test?
—
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This version of 1-wire temperature sensors has an address function allowing up to 64 addresses. Each address specifies the temperature sensor can be location. It does this by sampling the value of a resistor connected to ADD0 and ground .. see the data sheet for specific values.
I have updated library files to include a getLocation function. It samples the resistor value and writes the address to the 6 lsb bits in the status register. To access this you have to read the scratchpad .. the address located at scratchpad[2]
DallasTemperature.zip
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