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Subject: Re: AW: JB not starting with remote pin connected ?
From: Matthias.Klumpp_at_gmx.de
Date: 2004-06-23


Hi Sophana,

> >I had a more close look to the signal. In fact there is a short send
> command
> >
> that's probably your problem

Not probably, it IS my problem ;-))

> >If you apply 5V direct to the remote input of the JB, there were no
> >damages?
> >
> I use a 10k pull up resistor. applying 5v through a resistor will never
> damage your device, since it is protected by clamping transistors for
> electrostatic protection.
> Very often, 3.3v devices are made direct compatible with 5v devices by
> using special transistors on the positive side.

Hmmmmm......

> >Ah, so my low level of 0,7V is maybe too close to Vil, that might cause
> >communication problems in some models.......
> >I think, I should modify that OC stage to soemthing that has a real 0V
> >low state....
> >
> the more you will be close to the voltage limit, the less your design
> will be tolerant to noise induced by several environemental factors.
> But it can work that way.

I once did a test with a JBR of a friend of mine who bought it at Ebay.
The remote was not working, but I'm not sure if it was due to a connection
problem or maybe exactly because of the low level passing beyond TTL's 0,8V
level.....

In my JB Studio I don't have problems at all.

> >What do you think would be better:
> >- Simply connecting the UART 5V directly to the remote pin (without OC
> >stage
> >at all) ?
> >
> This can work and I even think it is the best and simplest solution.
> Simply place a 2k to 10k resistor for protection between both pins.
> Do you use bidirectionnal communication?
> If not there will be no problem at all since there is only 1 transmitter
> so no electrical conflict.
> If yes, collisions (if any) will be protected by the resistor you will
> place between both outputs.
>
> >- Designing a double npn transistor stage with last trans. as "real" OC ?
> >
> If you want a "real" open collector this is the solution indeed. But a
> lot of components: 3 resistors + 2 transistors.
> This is only needed if you absolutly want to have a real low level
> during collisions of 2 transmissions.
> Some protocols need that low level.
> You don't need it here...

I'll think about it....

THX

Matthias

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