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DS1820 or DS18B20

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27 October, 2010 - 13:55
Alanmh
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Reading, United Kingdom
Joined: 7 Jul 2010

I found some old temp sensors in the drawer and have tried to use them but I am getting "?" in the text field. They are DS1820 not DS18B20 - is there a significant difference? I have looked at the data sheet but I cannot fathom what the difference is.

The new sensor is at the end of a longish run, although there is only one sensor, so I dont think the length is significant?

Thanks in advance for any thoughts on this

Alan

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27 October, 2010 - 14:14
#1
derek
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Glasgow, United Kingdom
Joined: 26 Oct 2009
Try a short bus length

I've only ever tried the 18B20 parts. However, i reckon that the 1820s should be OK.

Do try a bus length of < 1ft first ... reduces the variables.

Derek.

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27 October, 2010 - 14:59
#2
Alanmh
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Reading, United Kingdom
Joined: 7 Jul 2010
I had been experimenting with

I had been experimenting with a short length <1m, and got the occasional "?" - not as many as now, but too many to be any use

will try again <1ft if I can find a 3.5mm stereo jack

 

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27 October, 2010 - 21:29
#3
Alanmh
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Reading, United Kingdom
Joined: 7 Jul 2010
Ok, I  have ordered a couple

Ok, I  have ordered a couple of 18B20's from Ebay - they may take a while to come so will try and get a few moments to stick the one I have on a bit of ethernet to see if that works.

It seems that the  1820 is working about 50% of the time, enough to give a bit of a trace for outside temp though

http://www.pachube.com/feeds/10591

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27 October, 2010 - 22:33
#4
Alanmh
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Reading, United Kingdom
Joined: 7 Jul 2010
I had a brainwave after

I had a brainwave after posting the last post and desoldered the one 18b20 I had from the stereo connector and soldered it onto an RJ45 plug. I plugged this into the socket in the garage that previously had the long lead out to the outside sensor (1820).

This sensor has been going fine for the last 20 mins without a single glitch.

My conclusion is that 1820s are not so good with this drive cct.

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28 October, 2010 - 04:01
#5
derek
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Glasgow, United Kingdom
Joined: 26 Oct 2009
Experimentation is key

Good job Alan.

I've been wanting to run a 'long' Cat5 based 1-wire bus. After reading the good article at http://www.1wire.org/Files/Articles/1-Wire-Design%20Guide%20v1.0.pdf
the following PCB was designed and sent off for fabrication

PCB layout

As well as providing an 'active' driver for the 1-Wire, this allows power to be injected to the bus via a USB socket. Prototypes should be headed my way soon. Fingers crossed!

Derek.

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28 October, 2010 - 09:25
#6
Alanmh
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Reading, United Kingdom
Joined: 7 Jul 2010
Excellent news Derek, I

Excellent news Derek, I eagerly await the news of the new boards. - Assuming they work can I put my name down for one of the first batch?

I spoke too soon about the 18b20 running ok, as soon as I went to bed it stopped running ;-(

I have measured the voltage at the sensor in the garage this morning and its a great 4.9V, I dont have a sope so I cant look at how clean it is.

Not sure exactly what your cct is soing, but I would guess its about cleaning the slew?

I havent read the whole article, but with my set up described below, maybe a 1-wire hub would be a good idea?

The set up I have here is that I have a patch panel and lan switch in the roof and most rooms have two ethernet ports wired back to the patch panel. I have bussed together 8 of the ports on the patch panel so that I can run POE wherever I like (plan is one internet and one POE to each room). So I can have a temp sensor wherever I want in the house and one outside.

So the run I have for the temp sensors goes from the office to the roof and back to the temp sensor location (this case the garage) I would guess the total run is about 15 metres.

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28 October, 2010 - 21:24
#7
Alanmh
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Reading, United Kingdom
Joined: 7 Jul 2010
Interesting observation

I tried adding a Schottky diode to the end of the run ( across the temp sensor data and gnd pins)

Things are much improved, but I still get a lot of "?"

But I have noticed that a string of "?" is always broken with an event and the "?" is always next to info messages on the xfx viewer.

What is the difference between info and event in this context? and why might the error be corrected by an event?

To be clear, no event shows a "?" always a value, but info class msgs can be either ,but always revert to "?" after 2 minutes - hang on this is the same as the timeout check that I have set for the temp sensor.

Will try lengthening this and report back

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5 April, 2011 - 18:47
#8
percih70
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Joined: 3 Jan 2011
The PCBs and setting the DS18B20 resolution

 

Hello Derek

Perchance do you plan to adding these PCBs to the shop? Id like to try one or 2 if I could? 

Also - do you know if its possible to set the resolution of the DS18B20 connected to the HAH, I’ve got some reporting every 0.5deg change while others report +_0.2deg changes – its possible to set the resolution in a Maxim windows appz, but it then seems to either be lost of over written on boot up? (0.2deg results in a lot of data).

 

Regards

 

Harry

 

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5 April, 2011 - 21:00
#9
percih70
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Joined: 3 Jan 2011
RJ45 PCB boards

 

Hello Derek

Perchance do you plan to adding these RJ45 PCBs to the shop list? Id like to try one or 2 if I could? 

Regards

Harry

 

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