wiki:Routers/TP-LINK/WR741ND
Last modified 14 months ago Last modified on 06/15/2016 12:30:24 AM

WR741ND

is a TP-LINK router with a single antenna and is the cheapest in WR series. There are several hardware revisions, v1.* having the old rectangular case and v2.* having the new UFO case.

Two screws beneath the rear rubber pads are to be removed, for the case to be opened.

WR741ND v2.4

This router is hardware wise similar to v1.x, but is in a nicer rounded chaises.

001 002

The package contains the router, a power supply, a 5dB omni antenna and an ethernet cable. Since v2.0 there is also a power switch on the router itself, according to a new EU directive.

Hardware characteristics

CPU Atheros AR7240 @ 350 MHz
RAM 32MB
Flash 4MB
LAN 4x 100Mbps Auto MDI/MDIX
WAN 1x 100Mbps Auto MDI/MDIX
WiFi 802.11 b/g/n 150Mbps (130Mbps real) 20dBm - 100mW
Dimensions 174 x 118 x 33 mm

Power characteristics

TODO: Measure power usage

The power adapter is rated 9V @ 0.6A . The router can be powered from a battery.

Disassembly

  1. remove the antenna
  2. remove two rear rubber pads
  3. remove the screws
  4. pry open the router on the rear side (where connectors are), the plastic will pop off

003 004

005 006

LAN protection

LAN ports are protected and galvanic ally isolated with transformers, that are center tapped and protected with a variac.

4x LAN Mentech electronics H2001DG isolation transformer

Versions of transformers may change even within a hardware revision.

To power the router via PoE, resistors (R90, R92, R131 if the router is powered via WAN port, R6-R17 if the router is used as a PoE splitter) located between isolation transformers and LAN/WAN ports have to be removed, because they connect pins 4,5 and 7,8 via 75Ohm resistors to varistors, that serve for ESD protection. They can be simply unsoldered. In the next step, ethernet port pins should be connected approprately to the power supply input on the board.

Serial port

Serial port is available on the router board, since v2.2 there is no standard 4 pin connector, most probably to simplify the circuit, but making its use slightly more demanding. There are two test points TP5-RX (receiving signal) and TP4-TX (transmitting signal), both work on 3.3V level, therefore the serial port is not directly compatible with standard RS232 devices (use max3232 or similar) nor 5V uart (use 3.3<->5V level shifter).

There is no pull-up resistor required for this routers serial port.

Power supply is taken from an empty capacitor pad, that is located in a non-critical/noise-prone circuitry. It can be sourced elsewhere from the board, but this was recognized as the most straightforward location.

Connections:

TP4 - TX, TP5 - RX, VCC - 3.3V, GND - 0V

007 008

The end of arrow-line on TX marks the location of the TP4, arrowhead indicating the direction of communication.

009 011

USB

TODO schematic + USB mod

WR741ND v4.3

001 002 003

The package contains the router, a power supply, a 5dB omni antenna and an ethernet cable. Since v2.0 there is also a power switch on the router itself, according to a new EU directive.

Hardware characteristics

CPU Atheros AR9331 @ 350 MHz
RAM 32MB
Flash 4MB
LAN 4x 100Mbps Auto MDI/MDIX
WAN 1x 100Mbps Auto MDI/MDIX
WiFi 802.11 b/g/n 150Mbps (130Mbps real) 20dBm - 100mW

Power characteristics

Rotuer consumes between 0.5W and 1W, depending on the power supply voltage and load.

The power adapter is rated 9V @ 0.6A . The router can be powered from a battery.

The router contains an MP1482DS step down voltage regulator, with the voltage range from 4.75V to 18V. This are absolute maximum ratings, other components might not be able to withstand such a range. 5V to 15V should be a safe range.

Disassembly

  1. remove the antenna
  2. remove two rear rubber pads
  3. remove the screws
  4. pry open the router on the rear side (where connectors are), the plastic will pop off

003 004

005 006

LAN protection

LAN ports are protected and galvanically isolated with transformers, that are center tapped and protected with a variac.

4x LAN Mentech electronics H2001DG isolation transformer

Versions of transformers may change even within a hardware revision.

POE

To power the router via PoE, resistors located between isolation transformers and LAN/WAN ports have to be removed, because they connect pins 4,5 and 7,8 via 75Ohm resistors to varistors, that serve for ESD protection. They can be simply unsoldered. In the next step, ethernet port pins should be connected approprately to the power supply input on the board.

Serial port

Serial port is available via the standard 4-pin connector used in all TP-Link routers, with a minor modification required as the TX pin is not connected to the processors by default. Serial port works with 3.3V voltage levels, therefore the serial port is not directly compatible with standard RS232 devices (use max3232 or similar) nor 5V uart (use 3.3<->5V level shifter).

It is however directly compatible with Texas Instruments Launchpad UART.

No pull-up resistor is required for this routers serial port.

Modification for connecting the TX pin to the connection header require a wire to be soldered on the bottom side of the board between TP18 and TP28 as shown.

004 005

WR741ND v4.20

This router is very similar to version 4.3, only a slight difference in the serial port connectons and element palcement on the board. See 4.3 section for all other details.

001 002

003 003

Serial port

Serial port is available via the standard 4-pin connector used in all TP-Link routers, with a minor modification required as the TX pin is not connected to the processors by default. Serial port works with 3.3V voltage levels, therefore the serial port is not directly compatible with standard RS232 devices (use max3232 or similar) nor 5V uart (use 3.3<->5V level shifter).

It is however directly compatible with Texas Instruments Launchpad UART.

No pull-up resistor is required for this routers serial port.

Modification for connecting the TX pin to the connection header require a wire to be soldered on the bottom side of the board between TP18 and TP28 as shown.

005 006

WR741ND v5.0

TP Link made some more changes with this version. Firstly, there is 5V supply without power button.

The Switched-mode power supply war removed and therefore printed circuit board (PCB) is smaller - small enough to put in smaller casing.

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