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From: Pancho <Pancho.Jones@proton.me>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: Need help with PI PICO...
Date: Sat, 30 Mar 2024 16:26:39 +0000
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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.