Anyway Chad, it is not my responsibility to teach basic C skills. So
hopefully your Students were taught to understand why something like this
would / could fail. And how to figure out why. Honestly though. Any 6 year
old with a browser + know how to use google could figure this out in 2
minutes.
On Mon, Nov 2, 2015 at 9:00 AM, William Hermans <yyrk...@gmail.com> wrote:
> #include <stdio.h>
>
> int main(void)
> {
> const float max_val = 4096;
>
> float test = ((4024 / max_val) * 1.8);
> printf("%f\n", test);
>
> return 0;
> }
>
> $ gcc test.c -Wall -o test
> $ ./test
> 1.768359
>
>
> On Mon, Nov 2, 2015 at 8:59 AM, William Hermans <yyrk...@gmail.com> wrote:
>
>> Anyway, since you do not seem to know why that does not work.
>>
>> Math on two integer values can not give out a float value. This is not a
>> math problem, but a compiler behavior issue. Intentional or no, one value
>> in the equation brackets *has* to be forced to a float value as such.
>>
>> 1) ((4024 / 4096.0) * 1.8)
>> *OR*
>> 2) const float max_value = 4096; ((4024 / max_value) * 1.8)
>>
>> It's also why I suggested using a const above.
>>
>> On Mon, Nov 2, 2015 at 8:16 AM, William Hermans <yyrk...@gmail.com>
>> wrote:
>>
>>> really now. Prey tell, enlighten us then with your logic.
>>>
>>> On Mon, Nov 2, 2015 at 5:10 AM, Chad Baker <cmbak...@gmail.com> wrote:
>>>
>>>> No, I don't, but having taught programming for over 40 years, I know
>>>> that students would take your equation and plug it in and then be surprised
>>>> that they get 0 for an answer.
>>>>
>>>> On 11/1/2015 6:13 PM, William Hermans wrote:
>>>>
>>>> *Or 4024 * 1.8 / 4096?*
>>>>>
>>>>
>>>> Ok, so let us put this another way. Do you think that is clear when
>>>> written in code ? What if 1.8 were actually assigned to a constant
>>>> pointer ?
>>>>
>>>>
>>>>
>>>> On Sat, Oct 31, 2015 at 5:01 AM, Chad Baker <cmbak...@gmail.com> wrote:
>>>>
>>>>> Or 4024 * 1.8 / 4096?
>>>>>
>>>>>
>>>>> On 10/30/2015 12:18 PM, William Hermans wrote:
>>>>>
>>>>> By the way, the ADC gives out a value of 0-4095. So scaling voltage is
>>>>> really simple. Say you get a value of 4024 for a reading. In order to get
>>>>> a
>>>>> reading from 0-1.8v from this . . .
>>>>>
>>>>> ((4024 / 4096) * 1.8) or 1.768359375v
>>>>>
>>>>> The max voltage on the pins still can not exceed 1.8v, this is why one
>>>>> needs an opamp, or similar device to keep the input scaled down. But, in
>>>>> this manner you could even track large voltages. Hundreds or even
>>>>> thousands
>>>>> of volts, at the cost of resolution. Which unfortunately can not be
>>>>> avoided. So going by the above example . . .
>>>>>
>>>>> ((4024 / 4096) * 300) or 294.7265625v
>>>>>
>>>>> Does this make sense ?
>>>>>
>>>>>
>>>>> On Fri, Oct 30, 2015 at 9:59 AM, William Hermans < <yyrk...@gmail.com>
>>>>> yyrk...@gmail.com> wrote:
>>>>>
>>>>>> *BBB and Linux are new to me. One of the things I would like to do
>>>>>>> is compute a ratio between two voltages, each of which might exceed 1.8
>>>>>>> VDC. One solution might be to use DACs to sent feedback voltages to
>>>>>>> operational amplifiers that are supplied by 1.8 VDC. The goal is to
>>>>>>> determine the ratio as quickly as possible and without waiting for
>>>>>>> Linux to
>>>>>>> get around to it (waiting for the ADC to happen).*
>>>>>>>
>>>>>>
>>>>>>
>>>>>> What sample rate do you need ? If something around only a few
>>>>>> thousand samples a second. This can be done from userspace without using
>>>>>> the PRU's. You can even use mmap() with /dev/mem/ and directly manipulate
>>>>>> the ADC's registers, which can sample the ADC faster than 200ksps.
>>>>>> However,
>>>>>> the sample rate would not be as deterministic as using the PRU's.
>>>>>>
>>>>>> You can use a PRU to read the ADC's for sure. If you search the web
>>>>>> for Beaglebone PRU + ADC
>>>>>> , you will find many ways. People have been doing this for a long
>>>>>> time( since the beaglebone white ), and if you search this google group,
>>>>>> you'll even find full code for something someone called "ADCcollector".
>>>>>> It's C, and PASM assembly, but is a very short / easy read /
>>>>>> understanding.
>>>>>>
>>>>>> As for how to physically connect to the ADC, I'd listen to
>>>>>> evilwulfile. He's been an EE for longer than many people on this group
>>>>>> have
>>>>>> been alive, and he knows his stuff ( I know him personally ). Don't risk
>>>>>> burning up your board, as I've seen several people on these groups do .
>>>>>> . .
>>>>>>
>>>>>> On Fri, Oct 30, 2015 at 9:43 AM, TJF < <jeli.freih...@gmail.com>
>>>>>> jeli.freih...@gmail.com> wrote:
>>>>>>
>>>>>>> Hi John!
>>>>>>>
>>>>>>> As Przemek mentioned, a simple voltage divider can scale the input
>>>>>>> voltage. Additionaly I use a LED (orange color) between the ADC input
>>>>>>> and
>>>>>>> ground in order to block overvoltage. (The LED starts to light up at 1V5
>>>>>>> and consumes full power at 1V8. 1 / 6 of the ADC resolution get lost (is
>>>>>>> less accurate), but the burning LED as indicatior is a nice side
>>>>>>> effect.)
>>>>>>>
>>>>>>> Regarding software you should have a look at libpruio
>>>>>>> <http://hackaday.com/2015/02/16/library-upgrade-to-pru-gives-fast-io-on-beaglebone/#comments>
>>>>>>> .
>>>>>>>
>>>>>>> BR
>>>>>>> --
>>>>>>> For more options, visit <http://beagleboard.org/discuss>
>>>>>>> http://beagleboard.org/discuss
>>>>>>> ---
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>>>>>>> https://groups.google.com/d/optout.
>>>>>>>
>>>>>>
>>>>>>
>>>>> --
>>>>> For more options, visit http://beagleboard.org/discuss
>>>>> ---
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>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Chad Baker Memphis, TN
>>>>> --
>>>>> For more options, visit http://beagleboard.org/discuss
>>>>> ---
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>>>>>
>>>>
>>>> --
>>>> For more options, visit http://beagleboard.org/discuss
>>>> ---
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>>>>
>>>>
>>>>
>>>> --
>>>> Chad Baker Memphis, TN
>>>>
>>>> --
>>>> For more options, visit http://beagleboard.org/discuss
>>>> ---
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>>>>
>>>
>>>
>>
>
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