AVR-Chat

Hi

I use sensor with output 0-10 volt 

plz Help me how to connect 0-10 volt sensor to internal A/D

(0-5 volt   working good but how to connect 0-10v)

Thanks

M.Juliat

On Thu, 22 Sep 2005 12:11:25 -0000 you wrote:

>Hi
>
>I use sensor with output 0-10 volt 
>
>plz Help me how to connect 0-10 volt sensor to internal A/D
>
>(0-5 volt   working good but how to connect 0-10v)
>
>Thanks
>
>M.Juliat

Connect a 10k resistor from the sensor output to the ADC input and 10k from the ADC input
to ground. that will halve the voltage on the ADC input pin. For safety I would add a
protection diode from the ADC input to the +5 volt line.
--
Ralph Hilton
http://www.ralphhilton.org
C-Meter: http://www.cmeter.org
FZAOINT http://www.fzaoint.net

On Thu, Sep 22, 2005 at 02:28:49PM +0200, Ralph Hilton wrote:
> On Thu, 22 Sep 2005 12:11:25 -0000 you wrote:
> 
> >Hi
> >
> >I use sensor with output 0-10 volt 
> >
> >plz Help me how to connect 0-10 volt sensor to internal A/D
> >
> >(0-5 volt   working good but how to connect 0-10v)
> 
> Connect a 10k resistor from the sensor output to the ADC input and 10k
> from the ADC input to ground. that will halve the voltage on the ADC
> input pin. For safety I would add a protection diode from the ADC
> input to the +5 volt line.

If he uses the internal 2.56v reference then try 20k in series with the
sensor to the A/D input and 6800 from there to ground. Should give a max
of 2.54 volts at the A/D input. But I've found ATmega64 internal
references run 2.40 to 2.60 if powered from 3.3. YMMV.

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.

Ralph

Which way should the diode go - Anode to 5v or Cathode to 5v?

I'm guessing it's backwards (K to 5v) to block large V from coming into the
5v line, kinda like the flyback/free-wheeling diode on a relay or motor,
right?

> -----Original Message-----
> From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com]On
> Behalf Of Ralph Hilton
> Sent: Thursday, September 22, 2005 8:29 AM
> To: AVR-Chat@yahoogroups.com
> Subject: Re: [AVR-Chat] connect 0-10 volt sensor to internal A/D
>
> For safety I would add a protection diode from the ADC input to the +5
volt line.
> --

On Thu, 22 Sep 2005 09:45:41 -0400 you wrote:

>Ralph
>
>Which way should the diode go - Anode to 5v or Cathode to 5v?
>
>I'm guessing it's backwards (K to 5v) to block large V from coming into the
>5v line, kinda like the flyback/free-wheeling diode on a relay or motor,
>right?

It goes with the arrow pointing to Vcc (K to Vcc). Yes, it stops excess voltage by
shorting it to Vcc.
--
Ralph Hilton
http://www.ralphhilton.org
C-Meter: http://www.cmeter.org
FZAOINT http://www.fzaoint.net

--- In AVR-Chat@yahoogroups.com, Ralph Hilton <ralph@r...> wrote:

> Connect a 10k resistor from the sensor output to the ADC input and 
10k from the ADC input
> to ground. that will halve the voltage on the ADC input pin. For 
safety I would add a
> protection diode from the ADC input to the +5 volt line.

...if you look at Atmel's Application Note #182 you can see that the 
built-in protection diodes of AVRs are able to handle currents up to 
1mA. If you limit the current from/to the pins with your external 
resistor to that (at max. input Voltage including some healthy safety 
margin), you won't need the extra diodes.

HTH,
Stefan

On Fri, 23 Sep 2005 21:08:19 -0000 you wrote:

>--- In AVR-Chat@yahoogroups.com, Ralph Hilton <ralph@r...> wrote:
>
>> Connect a 10k resistor from the sensor output to the ADC input and 
>10k from the ADC input
>> to ground. that will halve the voltage on the ADC input pin. For 
>safety I would add a
>> protection diode from the ADC input to the +5 volt line.
>
>...if you look at Atmel's Application Note #182 you can see that the 
>built-in protection diodes of AVRs are able to handle currents up to 
>1mA. If you limit the current from/to the pins with your external 
>resistor to that (at max. input Voltage including some healthy safety 
>margin), you won't need the extra diodes.
>
>HTH,
>Stefan

True, I read that note some time back.. However it is very easy for people new to
electronics to exceed that. On a test board playing around it is better to be safe that
sorry.

Personally I take my chances and if I blow the chip then I just plug in another but if
someone is on a limited budget and new to the scene then a protection diode might save
them buying a new AVR.

I blew out 2 chips this month due to errors on my part. But I have the budget to cover it.
Students don't. So if someone sounds like they are learning then I give them advice which
seems appropriate. I remember my student days when I would have to add up the cost of an
OC71 and every resistor in my project. But that was more than 30 years ago. A diode is
cheap and will probably short out saving the AVR if there is a problem.


--
Ralph Hilton
http://www.ralphhilton.org
C-Meter: http://www.cmeter.org
FZAOINT http://www.fzaoint.net

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