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Rockbox mail archiveSubject: AW: AW: AW: AW: Still Problems with AJB RemoteAW: AW: AW: AW: Still Problems with AJB Remote
From: Matthias Klumpp <Matthias.Klumpp_at_gmx.de>
Date: Wed, 14 Jul 2004 21:05:46 +0200 Hi Jörg, # -----Ursprüngliche Nachricht----- # > # > +5V # > | # > +-------------------------------+ # > | | # > +-+ +-+ # > | |22k | |4.7k # > | | | | # > +-+ +-+ # > +---------------------+ | # > +-+ | | # > | |12k | | # > | | | | # > +-+ | | # > | | | # > | | | # > --- | | # > |G | # > ------ | # > D| |S | # > uC Out port--------+ +--------+-- AJB remote # > # > Like this ? # # Almost. You need to swap the values of the divider. Yeah, I was recognizing this morning when I tried to simulate it in PSPice. # And I forgot to mention you should have a pullup on the uC side, too. Even so my PSPice simulation shows, that the output level is only going up to 0,7V. In the simulation I'm using a IRF150 (n-channel MOSFET) due to the reason I only have a demo version of it. Is this why I do have that difference of the output level, or is there still something wrong ? # Hmm, the circuit is bidirectional, for open collector on both # sides, which is not exactly what you want. Your uC serial output is a plain driver. Well bi-directional would not hurt. The thing more important is, that I need a circuit that is working with both Jukeboxes, with and without internal pull-up (like Studio Players and Recorders). # Forget what I said and simplify to this: # # +5V # | # | # +-+ # | |4.7k # | | # +-+ # | # | # Schottky | # uC Out port--------|<|---------+-- AJB remote # # The pullup won't hurt even if a box already has one. The diode will allow # your uC to pull the pin low, but will prevent it from being # driven with high output current to 5V. Instead it "gently" floats up via the pullup. Use a # Schottky because those have low voltage drop across, allowing for a better "low" level. Ok, I also did a PSPice simulation of this (with 1N4148 because the demo doesn't have a Schottky). The AJB remote level then toggels between high = 0,7V and low 0,612V ??? Well, I know, that these simulations are not very well done, but in previous cases it worked more or less like the final HW. Let me show you another possible solution: http://focus.ti.com/lit/an/slaa148/slaa148.pdf or http://focus.ti.com/docs/mcu/catalog/resources/appnoteabstract.jhtml?familyI d=342&abstractName=slaa148 both pointing to a TI application report that describes how to interface 3V devices by 5V devices. The easiest way the describe (page 4) is via a simple voltage divider. If you have a look into the calculation on page 4ff, they consider all kinds of tolerances and finally get to the result of a simple high ohmic voltage divider with 2x 1.2MOhm (also avoiding current into the device's protection diodes. Wouldn't be that the really easiest way ? THX Matthias _______________________________________________ http://cool.haxx.se/mailman/listinfo/rockbox Received on 2004-07-14 Page template was last modified "Tue Sep 7 00:00:02 2021" The Rockbox Crew -- Privacy Policy |