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General Category => General Discussion => Topic started by: Confusticated on 03 December 2012, 09:08:11 pm

Title: Dream\Guru\RasPi USB to 3v3 UART Adapter
Post by: Confusticated on 03 December 2012, 09:08:11 pm
This hack has been around for DSL Routers etc. a considerable number of years and is well documented elsewhere on the web, so this is just a brief guide applicable to the DreamPlug, GuruPlug, & Raspberry Pi. For brevity and clarity, the Raspberry Pi is referred to as RasPi and 'Plug' is dropped from the end of DreamPlug & GuruPlug.

A serial console is indispensable when developing systems to monitor boot progress and capture output for bug reporting and diagnosis. Most usefully, access to a 'Linux Console' enables repairs when networking has been broken, or provide a network connection when no actual physical network device exists (ideal for RasPi Model A). Specifically for the Dream\Guru, a serial connection can be used to easily change the u-boot environment variables or re-flash, even unbrick a Dream or a Guru using u-boot's 'kwboot' serial transfer tool.

Obtain a suitable connector for the Dream\Guru UART Port.

Obtain a genuine 'Nokia DKU-5' Mobile Phone Data Cable for £12+, this usually includes a 8cm Windows Driver CD.


Take a punt and obtain any of the following types of China Export 'Genuine Nokia Mobile Phone Data Cable' for £2.50+ (note, the giveaway is the price, these are genuine 'China Export' cables NOT genuine 'Nokia' cables).


The electronic circuitry will probably be *nothing* like the genuine Nokia equivalent part, and will most certainly not identify itself as such, requiring different driver setup (hence the reference to 'take a punt' above, you will have to work a little harder (Windows users may be provided a URL to download drivers, rather than be provided with the CD).It is vital that the data lead interfaces at a voltage of approximately 3v3, higher voltages will damage your Dream\Guru\RasPi.
Title: Re: USB to 3v3 UART Adapter
Post by: Confusticated on 03 December 2012, 09:08:39 pm
Connect the USB data cable into your PC (leaving the Mobile Phone PopPort plug disconnected). On Windows, install any provided drivers as prompted. Note if the USB device is enumerated (detected) and whether a serial device is created (/dev/ttyUSB? /dev/ttyACM? or for Windows, COM?).

If the serial device is created it will be possible to start your Serial Terminal Application of choice without having the Dream\Guru\RasPi powered up, simplifying use. Otherwise it will be necessary to hold the Dream\Guru\RasPi 'reset' button whilst powering up (to supply 3v3 to the USB UART) and starting the Serial Terminal Application (which will require the serial device to pre-exist). If this is too inconvenient, the somewhat tricky alternative is to splice in a 5v to 3v3 voltage regulator taking it's feed from the USB port with the output to the wire originally connected to PopPort pin 4 to adapt the data lead to the 3 connection type. See Below.

Disconnect the USB data cable. Cut off the PopPort plug leaving a tail, strip back the wires and use a multimeter\continuity tester to map the wire colour against the PopPort plug pins to identify them (pins 1 & 2 are absent, start counting from 3).
If pin 4 of the PopPort plug is not connected, the data cable is the 3 connection type (any connections to PopPort pins 3 & 5 can be disregarded).

Depending on which type you have
3 wire connection: Uses 5v from USB with internal voltage regulator supplying 3v3 (DKU-5).
4 wire connection: Uses 5v from USB and 3v3 from the Dream\Guru\RasPi.
Title: Re: USB to 3v3 UART Adapter
Post by: Confusticated on 03 December 2012, 09:09:01 pm
Connect the 4-Way 1.25mm pitch Molex Picoblade connector, if you purchased the replacement J-TAG leads from New IT, they will probably be colour coded as below (check yours against the image, carefully, the orientation of the Molex Picoblade connector is not obvious). On the Dream, pin 1 of the UART Port is nearest the power supply. On the Guru, pin 1 of the UART Port is nearest the J-TAG Port.

UART Socket                     PopPort Lead
1 Black         GND             8 GND
2 Yellow        RXD In          6 TXD Out
3 White         TXD Out         7 RXD In
4 Red           3v3 Out         4 3v3 In (not required for DKU-5)

There are multiple connector and pin choices for the PasPi, select whichever one pin is the most convenient for each of the GND and 3v3 connections.
Pin 1 is nearest the SD Card, with all even number pins next to the edge of the PCB.

RasPi P1                         PopPort Lead
6\9\14\20\25    GND              8 GND
10              RXD In           6 TXD Out
8               TXD Out          7 RXD In
1\17            3v3              4 3v3 In

If for any reason you are unsure of the connections, create a temporary test cable by soldering 270 Ohm resistors in series with each wire to restrict current flow.

Title: Re: USB to 3v3 UART Adapter
Post by: graemev on 04 December 2012, 10:18:15 am

Just what I want ... on so many levels:

1: I like to have perm serial access ... I bought a JTAG box, but it's a pain to have all that "stuff" connected (JTAG box)
2: I have a CA-42 (from my old Nokia)

... only issue. I bought China clone CA42 ... but I also bought a REAL CA42  ... is there an easy way to work out which is which (without a Nokia phone and windows software of course) .. ie is there a teltale pin ?
Title: Re: Dream\Guru\RasPi USB to 3v3 UART Adapter
Post by: Confusticated on 04 December 2012, 07:26:46 pm
Connect them one at a time, and run 'lsusb', the genuine Nokia should have 'Nokia' in  the idVendor string.
Title: Re: Dream\Guru\RasPi USB to 3v3 UART Adapter
Post by: apemberton on 06 December 2012, 07:45:34 pm
Oh dear! I got a Nokia DKU-5 clone from a phone shop which used an Arkmedia(?) conversion chip. Unfortunately it is not supported by Windows 7 and not at all by 64bit windows. Drivers are not available any more. So while it wasn't expensive, it is a bit of a chocolate teapot and has been dumped.

Nowadays I use the serial port of a Guru/Dreamplug JTAG adaptor with a kludged connector to the device I want to link at 3.3V.