Messages

1

Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: April 03, 2006, 11:11:02 pm »

Code: [Select]

1.BT ground disconnected, +5V connected:                  59mA

Hmm, this is more than expected but proves my guesses.

BTW, I've completely forgot that we're talking about powering up USB module which should work even from 4.4V volts.  This allows one to use cheap PNP like 2N2907 or BC807 in place of MOSFET (looking at schematic "C": connect emmiter instead of source , collector instead of drain, add an 1k resistor between collector of VT4 and base of VT3).

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: April 01, 2006, 10:51:57 pm »

I have one question, thou - I'd like to use schemantics "A" for bluetooth module, since it has less number of components and thus takes less space. But since 5V is connected all the time, can some amount of current leak thru the transistor?

When thansistor is closed the leakage currect are very insignificant.  However, I'm still worry about leakage through data lines - could you please to try to break +5V line, connect a multimeter in it and meausre how much current flows when transistor is off (or just disconnect the ground) ?

If you would like to keep schematic "A", I also would recommend to check how GPIO line behaves on boot - is it tied to +3.3V via resistor (or may be to ground) ? If not, it is recommended to insert a 10k resistor between GPIO and GND to prevent chaotic power supply to the buletooth module during reboot. Schematic "C" need it less, because bipolar transistor connected with common emitter have very low input resistance.

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: March 31, 2006, 09:13:44 pm »

IFDS6990A seems to work fine, but I'll try to measure the current leakage when gate is closed, I'm alitlle bit puzzled as of why wi-fi module signals on USB data lines when ground is supposed to be disconnected...

Because there are pullup resistors on either D+ or D- line as per USB standard.  Thats why one usually disconnect +5V bus  .

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: March 30, 2006, 10:53:21 pm »

- Toshiba TPC8203, TPC8005, TPC8002,
- International Rectifier IRF7811A, IRF7805
- FairChild Semi FDS6990A

Capabilities of IRF* are exsessive for this task, TPC* are suitable and FDS6990A are the best from this list.  But all of them are relatively high power MOSFETs and have large values of input and reverse transfer capacitances.  If I had a choice, I'd better be used something like NDS351AN from fairchild.

It is always good idea to place resitor in series with gate.

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: March 30, 2006, 09:37:28 pm »

On the same dead PCB I found the FairChild Semi's FDS6990A, which is a dual N-channel MOSFET with logic level GATE input.

Please note, that this transistor have very large input capacitance of 1235pF and series resistor (about 1k) between GPIO and gate are mandatory. If it missing, the GPIO pin may latch and blow the entire processor.

Also, you may wish to check if no current drawn for 5V bus via data lines when device is  not powered.

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: March 30, 2006, 12:10:13 pm »

Thank you for helping me out!

np

1. Why do we need s NPN transistor AND a P-ch MOSFET? Can we simplify the schemantics by using a sole N-ch MOSFET? Can then we just connect active-high signal from GPIO pin directly to GATE pin of MOSFET (assuming that it's the logic level input, we don't need a resistor?). SOURCE pin of the MOSFET then would be +5VDC source, and load would be connected to DRAIN pin? Can this schemantics work, or I'm missing something? (sorry, as you can see I lack the basic knowledge of electrical engineering).

No, this will not work.  The MOSFET controlled by voltage difference between source and gate, when Gate is above (more positive than) Source by threshold voltage, the transistor starts to turn on. N-Channel MOSFET will work fine in the schematic "A" (replace pins like this base-gate, emitter-source, collector-drain), but this will disconnect ground wire from the device. Not sure if this is acceptable.

P-Channel MOSFET controlled similary, just reverse all voltage polarities.

2. Speaking of MOSFETs, I'd probably like to use a dual channel one to control both modules and save some space. If I have a chance to select from different MOSFETs (i.e. can order any MOSFET made by FairChild Semi), what are the most important characterictics to look for? Obviously, I'd like to minimize current leakage in OFF state and voltage drop under load in ON state. Does it mean that the lower value of "Drain-to-Source ON resistance" is the better?

At first, you should look at drain current and select a device wich allows at least Imax *1.2.  Most modern MOSFETs have negligible "Drain-to-Source ON resistance" but it wouldn't hurt to verify volatge drop: Vdrop = Imax * Rdson (0.1V = 0.5A * 0.2Ohm).
Please note, that Rdson depends on gate voltage when it near gate threshold voltage and this depedency always represented graphically in datasheets. As for leakage in the off state - this will be very small value if transistor is closed.

What do you think about using FDS6910? It's a dual N-channel MOSFET in SO-8 package. It has "Drain-to-Source ON resistance" of only 0.017 Ohm which if I understand it correctly would give it 2.5VA * 0.017 Ohm = 0.0425V voltage drop @ 500mA load?

A bit different: Vdrop = 0.5A * 0.017Ohm = 8.5e-3V (by Ohm's law).

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: March 29, 2006, 11:26:04 pm »

I have a 1K resistor between GPIO output (active high) and transistor's base. That's pretty much all the schemantics.

 Now the problem I have: switching ON and OFF via GPIO works fine. And while BT module seems to be working as expected, the Wi-fi module is actually not behaving well. Some of the hardware ops fail, and it might look like it's not getting the sufficient current from the transistor. If I connect it directly without the transistor, it works fine.

Unfortnunatelly, you haven't specified how other pins of the transistor are connected, so we have two variants (see attached image).  Variant "B" will not work properly because it can't deliver 5V at all (only something about 2.6V) and I'll assume that it
is variant "A".

You're correct that this circuit can not supply 0.5A current without significant voltage drop.  Look at datasheet for values of collecter-emitter saturation voltages at given base and collector currents. With 1k resitor in base it can be about 1.5V.  Given that this transistor sits in the ground wire this can't work well indeed.

Can anyone recommend any particular circuit schemantics or components? I'm thinking of something as simple as possible via PNP or NPN transistor, or maybe MOS FET.

Since the requirement to have very low voltage drop at relatively high current with space restrictions, I would recommend schematic under letter "C". With FDN358P mosfet (fairchild) it will eat only of 0.1V at 0.5A.

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: March 07, 2006, 03:12:50 am »

Well, scratch that - the problem seemed to be unrelated to power supply. I got the internal wi-fi module working when powered from that regulator.

Ok.  You may try to measure voltages before and after 3850 to get the picture.   If that will not reveal any problems, then the problem might be in too large voltage spikes on USB power line during various modes of operation.  These can be identfied only with a scope.

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: February 27, 2006, 03:21:52 am »

Take a look here:

Nice work Albert!

About your concerns about 3850 power dissipation: if it powered from 5V rails we can assume that it will be in 4.9 - 5.6V range.  For input voltage below 5.17V power dissipation will be 0.5A * 0.17V = 85mW which will get the chip slightly warm.
At input of 5.6V it will be 0.5A * 0.6V = 300mW which isn't also very high.  Unfortunately, datasheet doesn't specify case thermal resistance to ambient so I can only guess that the chip temperature will be within 60C which is well in range of working
temperature.  In addition, this IC have thermal protection, so it should be safe to draw 500mA from it.

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: February 21, 2006, 09:23:15 pm »

I wired a Prism3-based 802.11b usb module and it ...

WORKS WORKS WORKS WORKS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Man, you rule!

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Hardware Mods / Stuffing Serial Bluetooth Module Inside C1k Casing

« on: July 01, 2005, 04:54:59 am »

It looks like there're only  two of us on this forum who are interested in the subject

Nope, I'm sure there are a lot of interest in it.  I'll follow your's research to stick BT module in my C3000 (if it will fit in it).

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C1000/3x00 Hardware / Sl-c3000 Screen Flickering

« on: June 23, 2005, 08:36:02 pm »

I've noticed something like that with AC adapter plugged in. The reason was hidden in the DC jack which had poor connection.
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Further investigation showed that the real reason of flickering is different.  It reliably appears when CPU heavily loaded (say by gcc) for about a hour.  After some time after load is gone flickering are also gone.  So, I guess this defect related to overheating of some component(s) inside Zaurus.  The ambient temperature in my tests were about 28C.

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C1000/3x00 General discussions / Belkin Usb To Lan Adapter

« on: June 23, 2005, 11:27:19 am »

I'll include this and the pegasus driver into the netswitch package to make it even simpler for other users.
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That would be nice indeed.

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C1000/3x00 General discussions / Belkin Usb To Lan Adapter

« on: June 23, 2005, 12:30:02 am »

I've found that netswitch package works fairly well (the above hotplug code not needed), but sometimes USB card fails on resume (cacko rom 1.23b1).  The following simple code placed in to /usr/bin/netresume allows manual restart:

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#!/bin/sh

rmmod usb-monitor
insmod usb-monitorIn addition, symlink added to /etc/apm.d/resume.d do this automatically:

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ln -s /usr/bin/netresume R50usbnet

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Cxx0 General discussions / C860 Charging Problem (not Battery)

« on: June 23, 2005, 12:15:27 am »

This is easily fixed by replacing a few capacitors.

Could you please elaborate a little bit more ?  Which capacitors ?  An electrolytic ones ? If they die in the normal operation modes then shame on Sharp