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Subject: RE: remote control
From: Stuart Tedford (stuart.tedford_at_piresearch.co.uk)
Date: 2002-10-14


Sorry, I have to answer this...

> -----Original Message-----
> From: Andreas Zwirtes
>
> We should not limit the interface by designing two resistors into the
> cable. Here some resons why:
>
Don't you mean "we _should_ limit the interface", surely having the
resistors in the remote is limiting the remotes interface - rather than
having a standard UART interface?

> First point is that I already have plans for the charger
> circuit that we
> might need and for a short circuit protection.
>
I agree that short circuit protection would be great, but I don't see how it
needs to have the resistors on the remote rather than the cable - but I'm
not a hardware guy.

> Second point is that resistors are the all time cheapest
> parts, so why
> not put them on every PCB and every interface? That would
> ease the cable
> production. It is very annoying to solder resistors into a
> cable, but no
> problem to put two resistors on a PCB.
>
In the quantities we're talking about here, I don't think this is a big
problem, and for people like me it is easier to solder a cable together than
to know what to do with a PCB etc especially if it's SMD.

> Third point is that the smallest remote i can guess doesn't even have
> room for the two resistors in the plug. I'm thinking of a PCB with a
> very small Lithium battery that is only about 2-3 square
> centimeters in size.
>
I guess for something this small and limited, there is no point in providing
a standard UART interface becasue it probably wouldn't be very useful for
controlling a PC or something, so yeah, I agree with you here - size it the
most important thing in this case.

> Fourth point is that we could use a very small two pin
> connector without
> audio or an also very small four pin connector with audio. But with 6
> pins you'll have a problem finding small connectors that are suitable
> for small devices. In fact, you already have that problem with 4 pins.
>
RJ-11 (telephone plug) is quite small - and certainly small enough for a
remote sporting an LCD display.

>
> To Andrew:
> We both already agreed that the Archos must not send
> anything, when no
> remote or the original remote is connected. So in the very beginning,
> the remote must be master to initiatiate the first
> communication.
>
I also agree that the remote must initiate/maintain the whole protocol. It
is too dangerous to have the Archos toggleing the port pin if it isn't
guaranteed what is connected at the other end - It is more comms overhead,
but I'd rather not blow up my Archos.

I guess my main point is, why bother designing something for just one fixed
purpose, when it would be relatively easy to allow it to be used for others?
The adaptor cable was just one idea - if there is a better way to make the
remote more flexible for non-hardware people then I'm all ears.

Oh, and what I meant by a new protocol being trivial... I should have said
_relatively_ trivial. Becasue it would only be a software change in the
remote - rather than a hardware and software change if you wanted to connect
to a new device. And depending on the device - the required protocol might
be quite simple.

Stu.



Page was last modified "Jan 10 2012" The Rockbox Crew
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