HC-SR04 and FreeBSD

Patrick Tracanelli eksffa at freebsdbrasil.com.br
Tue Aug 26 23:21:24 UTC 2014

On 26/08/2014, at 16:27, Luiz Otavio O Souza <lists.br at gmail.com> wrote:

> On 25 August 2014 16:57, Patrick Tracanelli wrote:
>> On 24/08/2014, at 19:29, Evandro Nunes wrote:
>>>> On Sat, Aug 23, 2014 at 5:51 PM, Patrick Tracanelli wrote:
>>> Hello,
>>> As far as I know, for this specific ultrasonic sensor, you are missing
>>> to set the echo GPIO pin to high. This sonar sensor will bring it back
>>> to 0 when the triggered sound get back to the sensor (round-trip).
>>> So the correct sequence should be, in a loop:
>>> 1 - Set echo pin to HIGH
>>> 2 - Trigger the sensor for 10us (it means your 100ms is more than you
>>> need, but no, it won’t cause a problem)
>>> 3 - Wait until echo in is LOW
>>> When the sound come back to sensor, the device will LOW the GPIO pin again.
> No, this is not correct, setting a value to an input is a noop and
> when you need this kind of cooperation from both sides, you usually
> will be using a pull-up and open colector outputs (they never drive
> the output to 'high' to avoid short-circuits).

Yes, I was not clear, that’s why I did some tests and sent the other e-mail. You won’t set anything, you will measure how long it was set to high.

>> What you wanna do is to measure how long HIGH takes.
>> I just made a better test so you can actually "see" the sensor working. Run this more simple loop:
>> gpioctl -c 2 IN
>> gpioctl -c 3 OUT
>> gpioctl 3 0
>> while true ; do
>> gpioctl 3 1 ; sleep .10; gpioctl 3 0
>>   while [ $(gpioctl 2 | tail -1) -gt 0 ] ; do
>>    echo "..." #nada
>>   done
>> sleep 1
>> done
>> On a second shell, run this horrible cpu consuming loop:
>> sh -c "while true ; do /root/date-precisao && gpioctl 2 ; done"
> This one is okay,

That’s it, my best shot to be clear about this specific sensor behavior.

>> Yes, you are right, I personally agree some library with basic electronic functions would be very valuable to FreeBSD.
>> Good to read you will try to write something, I believe Rui Paulo's library is a good start to hack, reading GPIO device, detecting when a PIN is HIGH and measuring the time until it becomes LOW is probably a good starter challenge ;-)
> What we need is interrupt support so you don't need to keep reading
> the GPIO pin in a busy loop and just get notified when the pin change
> its state.
> I hope i can get this sorted out soon (it is being worked on).

Wow this is very good news Loos.

Is it something new to gpioctl or another utility? Do you need a sensor to sort it out? I can send you with that board we talked before.

>> One sensor I am trying to make work is DHT11 temperature and humidity, according to datasheet[1] on section 7, this "single-wire bi-directional" sensor seems to return a 32bit value which shall be calculated in 4 octets.
> I can help you with the DHT11. I have some DHT11 working with an AVR
> bridge which gives me the DHT11 data through I2C, this make the
> readings reliable. I hope GPIO eventually grow up so i can get rid of
> the AVR bridge. There are 5 octets with the Parity.

My DHT11 is just dead, Ill get a new one soon and I would like to see your schematics and code, if possible, on how you made it to work. Are you using on a BBB board?

>> This is a kind of sensor that deserves a library for sure (and FreeBSD deserves to have such a library) but hopefully not the kind of Arduino library which is device specific. A more generic library that reads a selectable 8/16/32bit value and returns it in different formats (decimal, hex, ...) would do the job for this sensor as well as other single-wire pin sensors.
> A generic library isn't always possible because each device encodes
> the data in its own format, the DHT11(/DHT22) is different than
> onewire and so on, but a good driver (if possible) for DHT11 would be
> useful.

I agree, it’s a cheap device and useful one.

>> [1]http://akizukidenshi.com/download/ds/aosong/DHT11.pdf

Patrick Tracanelli

FreeBSD Brasil LTDA.
Tel.: (31) 3516-0800
316601 at sip.freebsdbrasil.com.br
"Long live Hanin Elias, Kim Deal!"

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