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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Gah! Data sheets.
Date: Thu, 26 Sep 2024 04:04:06 -0700
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On 9/25/2024 9:46 PM, Sylvia Else wrote:
> I was looking at building a remote controlled volume control for use at home. 
> Probably won't happen, but I came across this device:
> 
> https://www.nisshinbo-microdevices.co.jp/en/pdf/datasheet/NJU72344_E.pdf
> 
> Page 7 gives the serial protocol. It mentions S and P bits, but as far as I can 
> see they're nowhere else defined.

Think:  Start and stoP.  Similar in function to start and stop
bits in a UART.  "framing"  What they refer to as "START" and "STOP"

> Further down the page, it describes an auto-increment function. That is the 
> only mention.

Likely the presence of multiple "data frames" in a message.  So, you would
likely send a single message that would include <gain> <volumeA> and <volumeB>
parameters in the same packet.  This saves the overhead of having to send a
second (and third) message to the same <chip_address> with differing
<select_address>s.

> At the bottom of the page it talks about the consequence of an audio signal 
> being inputted (sic) before (during?) power on. Hard to know exactly what the 
> intent is, but based on that, I'd be concerned that the device might latch up, 
> or otherwise misbehave, if there's any input before power on. Be great to build 
> a bunch of boards with this and then discover that some proportion are flaky.

Reading the prose *literally* suggests that the "initial conditions" of
the three "select address"es as laid out in the "INITIAL CONDITION OF
CONTROL REGISTER" might not be guaranteed.  Asserting the "mute" signals
during startup would work-around any such transients (until you had
a chance to intentionally set the control registers' constents)

> How many designers would conclude that this could be more trouble than it's 
> worth, and find something else?

I always like using LDRs for variable audio gain.  But, my applications are
usually for smooth muting and not specific gain settings.