Hi Gerald,
It is stated many times that the maximum voltage for the analog inputs
is 1.8V, will a zener diode of 1.8V be enough to protect the analog input ?
The chip will need a little head room above 1.8V (say 0.05V or so) for a
1.8V zener to protect it. Is there a little bit of head room above 1.8V
where the input would be saturated, but chip will not be damaged?
100omh
___ /\ /\ /\ /\________________________________ AIN[X]
\/ \/ \/ \/ |
___|__/
/ /\ 1.8V Zener
/__\
|
______________________________|____________________ AGND
Thanks,
Matthew
On Thursday, June 20, 2013 9:10:10 AM UTC+10, Gerald wrote:
>
> OH, eventually it will burn out and the processor will need to
> be replaced. If that is likely to happen, you may want to consider a
> voltage divider and a zener diode.
>
> Gerald
>
>
> On Wed, Jun 19, 2013 at 5:52 PM, Arnaud Soyez <[email protected]
> <javascript:>> wrote:
>
>> I think the voltage on the analog pin to the light sensor may have
>> been > 1.8V (probably around 3V) when too much light was coming in.
>> What do you think would happen on the ADC in that case? Wouldn't it just
>> fry?
>> I redid my whole circuit and so far all tests are good.
>>
>>
>>
>> 2013/6/19 Gerald Coley <[email protected] <javascript:>>:
>> > Not likely.
>> >
>> > Gerald
>> >
>> >
>> >
>> > On Wed, Jun 19, 2013 at 2:48 PM, Weboide <[email protected]
>> <javascript:>> wrote:
>> >>
>> >> Would there be any problems with the two sensors sharing the same AGND?
>> >> Can noise propagate through the GND pin?
>> >>
>> >>
>> >> On Wednesday, June 19, 2013 11:46:19 AM UTC-4, Gerald wrote:
>> >>>
>> >>> Put a storage scope on the analog signal and capture it to check the
>> raw
>> >>> data being fed into the inputs over time.
>> >>>
>> >>> You can also connect the scope and expose your sensor to various light
>> >>> levels and see what the output does,.
>> >>>
>> >>> Gerald
>> >>>
>> >>>
>> >>> On Wed, Jun 19, 2013 at 10:29 AM, Arnaud Soyez <[email protected]>
>> >>> wrote:
>> >>>>
>> >>>> Yes I did, that's why I picked those, since I didn't use the touch
>> >>>> screen controller.
>> >>>>
>> >>>> Do you think that for example when the light sensor is in direct
>> >>>> sunlight there is a lot of noise coming in and messing up the ADC?
>> And
>> >>>> you think using a pullup or switching to a higher pin would solve
>> >>>> this?
>> >>>>
>> >>>> Just trying to understand what I am doing wrong and what my solutions
>> >>>> are.
>> >>>>
>> >>>> 2013/6/19 Gerald Coley <[email protected]>:
>> >>>> > Yes.
>> >>>> >
>> >>>> > It is for the Touch Screen Controller mode which is the primary
>> >>>> > function of
>> >>>> > this interface.. Have you looked at the TRM?
>> >>>> >
>> >>>> > Gerald
>> >>>> >
>> >>>> >
>> >>>> >
>> >>>> > On Wed, Jun 19, 2013 at 10:14 AM, Arnaud Soyez <
>> [email protected]>
>> >>>>
>> >>>> > wrote:
>> >>>> >>
>> >>>> >> You mean the same setup but different pin for my temperature
>> sensor?
>> >>>> >> How would a pullup help in analog?
>> >>>> >>
>> >>>> >> 2013/6/19 Gerald Coley <[email protected]>:
>> >>>>
>> >>>> >> > You have the ability in the processor to connect AIN0-3 to a
>> >>>> >> > pullup. It
>> >>>> >> > is
>> >>>> >> > used in TSC mode. Move to a higher AIN number and see if the
>> same
>> >>>> >> > thing
>> >>>> >> > happens there.
>> >>>> >> >
>> >>>> >> > Gerald
>> >>>> >> >
>> >>>> >> >
>> >>>> >> > On Wed, Jun 19, 2013 at 9:58 AM, Arnaud Soyez
>> >>>> >> > <[email protected]>
>> >>>>
>> >>>> >> > wrote:
>> >>>> >> >>
>> >>>> >> >> P9_38 and P9_40 for reading ADC.
>> >>>> >> >>
>> >>>> >> >> 2013/6/19 Gerald Coley <[email protected]>:
>> >>>>
>> >>>> >> >> > Could be. Which pins are you using?
>> >>>> >> >> >
>> >>>> >> >> > Gerald
>> >>>> >> >> >
>> >>>> >> >> >
>> >>>> >> >> >
>> >>>> >> >> > On Wed, Jun 19, 2013 at 9:43 AM, Weboide <
>> [email protected]>
>> >>>>
>> >>>> >> >> > wrote:
>> >>>> >> >> >>
>> >>>> >> >> >> Could it be related to
>> >>>> >> >> >>
>> >>>> >> >> >>
>> >>>> >> >> >>
>> >>>> >> >> >>
>> http://hipstercircuits.com/noise-on-the-analog-pins-causes-the-adc-sampler-to-go-out-of-whack/
>> >>>> >> >> >> ?
>> >>>> >> >> >>
>> >>>> >> >> >>
>> >>>> >> >> >> On Wednesday, June 19, 2013 10:40:01 AM UTC-4, Weboide
>> wrote:
>> >>>> >> >> >>>
>> >>>> >> >> >>> Yes, using ADC ground for both.
>> >>>> >> >> >>>
>> >>>> >> >> >>> The TMP36 is connected to 5V DC though (but should always
>> >>>> >> >> >>> return <=
>> >>>> >> >> >>> 1.8V).
>> >>>> >> >> >>>
>> >>>> >> >> >>> 2013/6/19 Gerald Coley <[email protected]>:
>> >>>>
>> >>>> >> >> >>> > Are you using the ADC ground as your reference ground?
>> >>>> >> >> >>> >
>> >>>> >> >> >>> > Gerald
>> >>>> >> >> >>> >
>> >>>> >> >> >>> >
>> >>>> >> >> >>> >
>> >>>> >> >> >>> > On Wed, Jun 19, 2013 at 9:34 AM, Weboide
>> >>>> >> >> >>> > <[email protected]>
>> >>>>
>> >>>> >> >> >>> > wrote:
>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >> Using the analog pins on my BBB, i have a light sensor
>> >>>> >> >> >>> >> (resistor)
>> >>>> >> >> >>> >> and
>> >>>> >> >> >>> >> a
>> >>>> >> >> >>> >> TMP36 temperature sensor, both plugged as shown on
>> >>>> >> >> >>> >> adafruit.
>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >> Would there any reason (on a BBB) that the following
>> spike
>> >>>> >> >> >>> >> to
>> >>>> >> >> >>> >> 1.8V
>> >>>> >> >> >>> >> appear
>> >>>> >> >> >>> >> on both pins (and delayed)? This happened to me twice
>> now.
>> >>>> >> >> >>> >> Otherwise
>> >>>> >> >> >>> >> they
>> >>>> >> >> >>> >> work fine...
>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >> See the second chart at
>> http://beaglebone.codealpha.net/
>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >> I would understand that the light sensor could somehow
>> show
>> >>>> >> >> >>> >> 1.8V
>> >>>> >> >> >>> >> if
>> >>>> >> >> >>> >> it
>> >>>> >> >> >>> >> is
>> >>>> >> >> >>> >> too bright, but the temperature sensor suddenly climbs
>> up
>> >>>> >> >> >>> >> as
>> >>>> >> >> >>> >> well
>> >>>> >> >> >>> >> and
>> >>>> >> >> >>> >> shows
>> >>>> >> >> >>> >> 130 degrees Celsius! Is there any interference between
>> the
>> >>>> >> >> >>> >> ADC
>> >>>> >> >> >>> >> pins
>> >>>> >> >> >>> >> or
>> >>>> >> >> >>> >> GND's,etc..., or did I hit a fuse or something?
>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >> The down spikes at the end are when I blew on the
>> sensors
>> >>>> >> >> >>> >> and
>> >>>> >> >> >>> >> put
>> >>>> >> >> >>> >> my
>> >>>> >> >> >>> >> hand
>> >>>> >> >> >>> >> over the light sensor. And then it looks like the TMP36
>> >>>> >> >> >>> >> finally
>> >>>> >> >> >>> >> went
>> >>>> >> >> >>> >> down in
>> >>>> >> >> >>> >> temperature.
>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >> Arnaud
>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >> --
>> >>>> >> >> >>> >> For more options, visit http://beagleboard.org/discuss
>> >>>> >> >> >>> >> ---
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>> >>>> >> >> >>> >>
>> >>>> >> >> >>> >
>> >>>> >> >> >>> >
>> >>>> >> >> >>> >
>> >>>> >> >> >>> >
>> >>>> >> >> >>> > --
>> >>>> >> >> >>> > Gerald
>> >>>> >> >> >>> >
>> >>>> >> >> >>> > [email protected]
>> >>>> >> >> >>> > [email protected]
>> >>>>
>> >>>> >> >> >>> > http://beagleboard.org/
>> >>>> >> >> >>> > http://circuitco.com/support/
>> >>>> >> >> >>> >
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>> >>>> >> >> >
>> >>>> >> >> > --
>> >>>> >> >> > Gerald
>> >>>> >> >> >
>> >>>> >> >> > [email protected]
>> >>>> >> >> > [email protected]
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>> >>>> >> > --
>> >>>> >> > Gerald
>> >>>> >> >
>> >>>> >> > [email protected]
>> >>>> >> > [email protected]
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>> >>>> > --
>> >>>> > Gerald
>> >>>> >
>> >>>> > [email protected]
>> >>>> > [email protected]
>> >>>>
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>> >>>
>> >>>
>> >>>
>> >>> --
>> >>> Gerald
>> >>>
>> >>> [email protected]
>> >>> [email protected]
>> >>> http://beagleboard.org/
>> >>> http://circuitco.com/support/
>> >>
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>> >
>> >
>> >
>> >
>> > --
>> > Gerald
>> >
>> > [email protected] <javascript:>
>> > [email protected] <javascript:>
>> > http://beagleboard.org/
>> > http://circuitco.com/support/
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>
>
> --
> Gerald
>
> [email protected] <javascript:>
> [email protected] <javascript:>
> http://beagleboard.org/
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>
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