Can we have multiple 1-wire devices on single pin?

Arduino supports that, but I have not found anything about for that in PBP reference manual...
I want to hook up 4 pcs of DS18B20 to single pin. As I have read, each has unique identifier, so it should be possible, but how?

It is quite doable, you just need to write your own code. Do a search of the forum - I know there is a code example because I've used it 8-9 years ago. There are no native commands in any language I'm aware of. This is not PBP vs C or PIC vs Arduino.

Here is a program I wrote some years ago to do a search of 1 wire devices present on a single bus.

I've never understood the logic behind the find all the serial numbers function, unless you know what each device (using it's serial number) is measuring it seems pointless. For example in s asystem with three devices, one measuring ambient, one measuring input temp and another measuring output temp - how does it help to be able to determine the serial numbers of the devices when you don't know which ones which?

You just add one device at time. And search after you add one.

Exactly correct. What I do is scan each sensor 1 at a time and take the serial number and attach it to the sensor lead with a piece of paper under a piece of transparent film. That way I can replace any sensor in my system with another one and just change the serial number in the code.

True, but isn't it easier to know which serial as you install each device.

Works even better if you but the serial numbers in an array, easy to ammend, or add or iterate.

I want to use PIC16F1503 and have to chain thermometers due to pin count. I guess, running above, complex code might not be possible on this wimpy chip?

The task is as follows:
There are 3 fans with PWM input and tachometer output, MAX7219 display and array of buttons. Circuit will monitor fan rpm and adjust it according to individual thermometer reading.

I have 12 IO pins on that chip, I'm thinking about allocating them in the following way:
3 pins - hardware PWM outputs.
3 pins - tachometer inputs.
3 pins - driving MAX7219
1 pin (MCLR), used as ADCIN, to attach several buttons.
1 pin - relay driver, for emergency shutdown.

So I have only 1 pin, for attaching 3 DS18B20....

So... Do it....

Quote:

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Originally Posted by CuriousOne

I want to use PIC16F1503 and have to chain thermometers due to pin count. I guess, running above, complex code might not be possible on this wimpy chip?

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You can read address, without searching, if it is only one device present at bus. Just write command $33, and collect next 64bit. Do this 3 time, one for each sensor.
Connect all DS to bus.
Write $CC,$44 to start temperature conversion on all DS simultaneously.
Then use match ROM($55) followed by address, to read data from one DS.
Look at page 11 in this datasheet https://datasheets.maximintegrated.c...ds/DS18B20.pdf

I have an idea, fan tachometer output will be tied to VDD via 4.7k resistor, as DS18B20 should be. Fan outputs pulses not so fast, so what if I attach DS18B20 to same pin as fan tachometer output? and say, after falling edge of tachometer pulse, perform all DS18B20 stuff, while fan pulls pin high again?

I believe it takes ~750 Ms. to complete 1 conversion. With that being said, How are you going to discern if the next pulse is the tach output or the DS output?

Yes, so I came to different solution. I also have PWM output pin, which goes into fan PWM in. So I'll hook DS18B20 to it - When I need to use thermometer, I will stop HPWM output on that pin, read the thermometer and then resume HPWM operation. I guess, fan will have enough inertia to have no significant impact on it's rpm.

You do realize 750ms is three quarters of a second? Fan speed will be very wobbly.

Fan won't stop in absence of PWM signal. most fans, without PWM signal applied, will default to 30-50% RPM.

hello, you can read several ds18b20 sensors and execute the part of the control that you want to carry out, see the attached file the routine I use in a device for the control of air conditioning and lighting with serial communication.Attachment 8949

And a side question, can we use 1-wire protocol to communicate between 2 PICs?

The idea is to have the PIC as a master device and the PIC to request a communication.

So, with the available commands, it is not possible to make a PIC react as a slave 1-wire device.

You have to write your own code for that.

Ioannis