Stuffing Serial Bluetooth Module Inside C1k Casing

[sidmoraes]

Anybody tried to compare these photos?

https://www.oesf.org/forums/index.php?act=A...pe=post&id=1048 ( from this thread https://www.oesf.org/forums/index.php?showt...16&hl=bluetooth )

and

http://hypernote.com/gallery/zaurus/c3k_cl...C_0071.jpg.html

[albertr]

If you are wondering about these soldering pads...

https://www.oesf.org/forums/index.php?showtopic=17937&st=77#

-albertr

[speculatrix]

hmm.
so, basically, you can't fit the bluetooth adaptor whilst the internal CF slot is in use whether by microdrive or CF card - you'd have to use flying leads to the BT adaptor, or maybe a ribbon cable for a CF card to move it out of the area.

bummer.

[albertr]

C3x00:
I doubt that you can relocate the microdrive - there's simply not enough space elsewhere. But finding a place for a small BT module might be a possibility. In this case the flying leads can be used to connect it to BTUART lines.
C1K:
There're plenty of space available.

-albertr

[JohnX]

albertr: I was wondering if you've noticed any difference in reception for your internal wifi mod vs a CF wifi card? If there isn't a significant difference or the internal wifi dongle does better, then I might be interested in paying someone to solder a wifi dongle (and maybe bluetooth) into my C1000.  

[albertr]

I didn't do any RF tests, and I don't have any equipment for RF testing.
All I can express is my very subjective opinion.
-albertr

[albertr]

http://www.iral.com/~albertr/linux/zaurus/wireless/

was updated with info on BTUART tracing and some GPIO pins. I still don't have time to make more pictures to show how it looks inside the case, but will try to add it sometime later.
-albertr

[Da_Blitz]

very nice, now i know where to hack in my acellerometer

[albertr]

There were some questions asked via email. In case anyone else is interested, I'm posting answers to some of them here as well:

- BTUART speed: Billionton CSR BC2-ext module is working @ 921600 baud with BTUART on my C1K with BCSP protocol. It seems to work fine at that speed, I didn't notice any problems so far.

2. I was using 22 Ohm resistor array. I ordered samples from http://www.koaspeer.com/. They have a sample order page on thier website. I don't remember the exact part number, but I think it was either CN1J4KTBK220J or CN1E4KTBK220J (whichever has the smallest size). You might want to check with koaspeer if they have a local distributor and ask them for samples. I still have a few of them left, if anyone in the US needs it, please PM me with your shipping address, but please try to contact koaspeer or other manufacturer first.

-albertr

[albertr]

I checked the part numbers - the P/N from koaspeer.com is CN1E4KTBK220J .
-albertr

[albertr]

I think I might need some help from someone experienced in electric engineering. I'm trying to control the power to internal wi-fi and bt modules with GPIO pins via a NPN transistor. The transistor I was able to find in local Radioshack is MPS2222A (its datasheet is available here: http://www.ortodoxism.ro/datasheets/motorola/MPS2222A.pdf ). I think it looks as a close replica of 2N2222A, except that collector's continuous current is specified as 0.6A instead of 0.8A (for 2N2222A). 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.

Now here's the big question: Is the transistor I have is not good for powering up the wi-fi module? Maybe my simple schemantics are not good? Unfortunately, I don't have an o'scoope to check the actual signals.

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.

I can get NTB60N06L MOSFET that has 3V TTL logic level input (the datasheet is here: http://www.onsemi.com.cn/pub/Collateral/NTP60N06L-D.PDF ). Can it be used for this purpose? Is current leakage less with MOSFET than with silicon transistor? The other problem I see is that it's rather large, so it could be a challange to fit two of them inside the Z. Is there any smaller size MOSFET with logic level input that can be used and available for online ordering in the USA?

Any ideas, suggestions?
-albertr

[Boris]

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.

[albertr]

Boris,

Thank you for helping me out! Yes, I'm using the "A" schemantics from your drawing. After you explained it, now I can see why I'm having the problem under load.

So, if the MOSFET is the right way to go, may I ask you a couple of questions?

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).

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?

-albertr

[albertr]

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?
-albertr

[Boris]

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).