Forum - MCS Electronics

 

FAQFAQ SearchSearch RegisterRegister Log inLog in

How low can it go (temperature problem)?

 
Post new topic   Reply to topic    www.mcselec.com Forum Index -> Various
View previous topic :: View next topic  
Author Message
srecko

Bascom Member



Joined: 05 Sep 2007
Posts: 14
Location: Dolenjske Toplice

slovenia.gif
PostPosted: Wed Sep 05, 2007 12:58 pm    Post subject: How low can it go (temperature problem)? Reply with quote

Hello.

First cheers to all of you. I'm new to this group and I already have a question, that is bugging me for the past month.

I'm working on a project for meashuring wind speed. Everything is going well, but the temperature is bugging me a lot. It seems as that the oscillator stops running at about -10C. This is also written in the quartz crystal's datasheet. But I need this to work at least to -20C.

Does any of you have some hints on this problem?

All the hints will be deeply apprechiated.

Thanks in advance and best regards.

Srecko Lavric
Back to top
View user's profile Visit poster's website
rileyesi

Bascom Member



Joined: 19 Dec 2006
Posts: 398

blank.gif
PostPosted: Wed Sep 05, 2007 6:35 pm    Post subject: Reply with quote

Hi.

Can you add a heater to your system? If you have an enclosure, a simple light bulb connected to a thermostat might work. If not, I have seen some installations where a spot light is used to prevent the wind sensors from freezing.

What type of anemometer are you using?

Regards,

Pete
Back to top
View user's profile
srecko

Bascom Member



Joined: 05 Sep 2007
Posts: 14
Location: Dolenjske Toplice

slovenia.gif
PostPosted: Thu Sep 06, 2007 6:58 am    Post subject: Reply with quote

Hello.

Unfortunatly the heater is not an option, since this is battery powered device working mostly in powerdown mode. It only wakes up every hour and collects the data from the other microcontroller, working on 32.768KHz. The device consumes about 180uA of current when counting pulses. The anemometer is made with hall sensor, but I don't know it's exact type, since it is from my friend.

I will have to tackle with fuse bits, I heard that the oscillator's power can be increased. Also I will try to find some other crystal. Te 32.768KHz crystal is working down to -40C.

Thank you for your reply and best regards.

Srecko Lavric
Back to top
View user's profile Visit poster's website
Luciano

Bascom Member



Joined: 29 Nov 2004
Posts: 3149
Location: Italy

blank.gif
PostPosted: Thu Sep 06, 2007 12:45 pm    Post subject: Reply with quote

Hi,

What about using a 32.768kHz Temperature-Compensated Crystal Oscillator?

If the 32 kHz is used as clock source for the device, then just use "External clock".

If the 32 kHz is used as clock source for the Timer2 in asynchronous mode, then some
AVR chips can be asynchronously clocked with an external 32 kHz clock.

Example of 32 kHz Crystal Oscillator:
DS32kHz
32.768kHz Temperature-Compensated Crystal Oscillator
http://datasheets.maxim-ic.com/en/ds/DS32kHz.pdf

(Operating Temperature Range: -40C to +85C for the industrial version)

Best regards,

Luciano
Back to top
View user's profile
srecko

Bascom Member



Joined: 05 Sep 2007
Posts: 14
Location: Dolenjske Toplice

slovenia.gif
PostPosted: Thu Sep 06, 2007 12:56 pm    Post subject: Reply with quote

Hello, Luciano.

It looks, that I wasn't clear enough. I'm using two micros, one is running at 32.768KHz and it's working fine. The other is 3.6864MHz. This is the one which stops working at about -10C.

Today I downloaded a new datasheet for M168, since I suspected, that something is wrong with CKSEL fuse bits and I was right. The document had an error and today I will try to set CKSEL to 0111 and SUT to 01, since i use BOD. If this won't solve my problem, then I don't know what else to do then buying quartz with wider temperature range.

Thanks for suggestions and best regards.

Srecko Lavric
Back to top
View user's profile Visit poster's website
Luciano

Bascom Member



Joined: 29 Nov 2004
Posts: 3149
Location: Italy

blank.gif
PostPosted: Thu Sep 06, 2007 2:18 pm    Post subject: Reply with quote

Hi,

Make sure the crystal has the correct operating temperature range.

* * *

AVR042: AVR Hardware Design Considerations

http://www.atmel.com/dyn/resources/prod_documents/doc2521.pdf
(See section 5)

* * *

See also this Microchip application note:
"Making Your Oscillator Work"

http://ww1.microchip.com/downloads/en/AppNotes/00949a.pdf

Best regards,

Luciano
Back to top
View user's profile
srecko

Bascom Member



Joined: 05 Sep 2007
Posts: 14
Location: Dolenjske Toplice

slovenia.gif
PostPosted: Fri Sep 07, 2007 10:04 am    Post subject: Reply with quote

Hi!

Thank you for the application notes. They are very useful. I studied them thru and will follow the guidelines this weekend. I will also preform some tests too. I will let you know about results, since they might be useful to other users of this forum.

Best regards,

Srecko Lavric
Back to top
View user's profile Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic    www.mcselec.com Forum Index -> Various All times are GMT + 1 Hour
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum