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From: The Natural Philosopher <tnp@invalid.invalid>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: Need help with PI PICO...
Date: Sat, 30 Mar 2024 18:17:15 +0000
Organization: A little, after lunch
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On 30/03/2024 16:26, Pancho wrote:
> On 30/03/2024 09:17, The Natural Philosopher wrote:
>> On 30/03/2024 02:04, Jim H wrote:
>>> On Fri, 29 Mar 2024 10:49:13 +0000, in <uu66b9$83pi$3@dont-email.me>,
>>> The Natural Philosopher <tnp@invalid.invalid> wrote:
>>>
>>>> Maybe ascii art will help
>>>>
>>>> CONTROL=10µs
>>>> ____| |________
>>>>
>>>> RETURN = wahatever
>>>> _____|^^^^^^^^^^^^|____________
>>>>
>>>
>>> Assuming my bleary-eyed math is correct, 10µs is the length of one
>>> cycle of ultrasound at 100,000 Hz.
>>>
>> The width of that pulse is pretty much immaterial - its only a digital 
>> trigger, It doesn't send anything directly.
>>
>> The unit does that, and senses a high to the output. Then it transmits 
>> a squawk., When it receives an echo it switches that to low.
>>
>> Its a smart device .
>>
> 
> I think that is the part I was missing. I assumed it was like an analog 
> device, out pin was for send  and the in pin signalled it was receiving.
> 
> On reflection, the code makes sense if it is a smart device. The in pin 
> just goes high (or low) for the period between sending and receiving a 
> few micro seconds of the echo.
> 
> 
>> https://cdn.sparkfun.com/datasheets/Sensors/Proximity/HCSR04.pdf
>>
> 
> Not the most precise wording.
> 
> Having taken the trouble to understand. I might buy one to tell me if my 
> garage door is open. Buy an echo device that is, not a PICO.
> 
> 
Well hook it to a pico and tell a server via wifi that  the door 
is/isn't open!

It seems reiable so far.


Now running of 3 dry cells to see at what point the voltage gets too low 
for reliable pinging.


-- 
Canada is all right really, though not for the whole weekend.

"Saki"