Wireless Router

I have a couple of old routers that have been replaced by more advanced ones.  So it is time to hack them for other use.  A wireless router is an embedded computer with wireless connection; so it is good for IoT applications.  A lot of old inexpensive routers have 32MB RAM and 4MB Flash, which is rather limited for more advanced router application.  OpenWRT no longer supports this type routers.  It'll be good to branch off OpenWRT to support this type of routers for IoT.   We looked at one such router earlier.

Here we take a look at TP-Link TL-WR841N, Ver 9.2.  300Mbps wireless N router, with 4x 100Mbps ethernet ports.  The main components are

• Qualcomm Atheros QCA9533-AL3A SoC
• 24Kc MIPS processor with 64KB I-Cache and 32KB D-Cache at up to 650MHz
• 25MHz clock input
• 1.2V switching regulator for core voltage.  2.62V LDO for DDR1 and GPIO.
• RF 20/40MHz band 2.4GHz OFDM for 802.11b/g/n, 2x RX/TX
• Zentel A3S56D40GTP-50L 
• 256Mb (16Mx16) 2.5v DDR400 200MHz @CL3xTSOPII-66.  
• Spansion S25FL032P 
• 32-Mb 3V Flash memory QUAD I/O 80MHz clock 40MB/s.  
• BCD's AP3502E 
• 340KHz fixed frequency 2A synchronous buck converter
• 3.3V output

The PCB date code is 1434, about 2014 August time frame.  QCA9553 is more powerful and more integrated than AR9130 used on the other router.

J3 is a 4-pin UART connector,

1. TX (2.6V)
2. RX
3. GND
4. 3.3V

Note the I/Os are 2.6V.  TX has no problem driving 3.3V UART receiver; there appears to be a few resistors in series with the RX pin, so it could be driven with a 3.3V input, but it may be prudent to add another 1K resistor in series.

The last OpenWRT version for this router is openwrt-18.06.8.  We get the boot message from the UART, 

U-Boot 1.1.4 (Build from LSDK-9.5.3.16 at Nov 29 2013 - 10:46:36)

ap143 - Honey Bee 1.1

DRAM:   32 MB
Flash Manuf Id 0x1, DeviceId0 0x2, DeviceId1 0x15
Flash:  4 MB
Using default environment

## Booting image at 9f020000 ...

   Uncompressing Kernel Image ... OK

Starting kernel ...

[    0.000000] Linux version 4.9.214 (buildbot@0d27b924961c) (gcc version 7.3.0
(OpenWrt GCC 7.3.0 r7989-82fbd85747) ) #0 Thu Feb 27 21:25:59 2020
[    0.000000] bootconsole [early0] enabled
[    0.000000] CPU0 revision is: 00019374 (MIPS 24Kc)
[    0.000000] SoC: Qualcomm Atheros QCA9533 ver 1 rev 1

BusyBox v1.28.4 () built-in shell (ash)
  _______                     ________        __
 |       |.-----.-----.-----.|  |  |  |.----.|  |_
 |   -   ||  _  |  -__|     ||  |  |  ||   _||   _|
 |_______||   __|_____|__|__||________||__|  |____|
          |__| W I R E L E S S   F R E E D O M
 -----------------------------------------------------
 OpenWrt 18.06.8, r7989-82fbd85747
 ----------------------------------------------------- 

We can interact with it through the ash shell.  Next we'll try to rebuild the firmware from the source and start to tweak.

H632S-WC Weather Channel EZ Crank Radio Extreme

 

The crank is a 3-phase alternator driven by two-stage gears; the output is rectified by 6 diodes.   There is another diode between the bridge rectifiers and the output voltage.   The FM radio IC is CD9088CB, which can operate between 1.8V and 5V, drawing about 5mA.  The 8Ω 4W speak and earphone are driven by TDA2822M, a dual low-voltage power amplifier, which works down to 1.8V.  The rechargeable battery pack is a 3-cell NiMH for 3.6V.   Most other components are for the radio.   The rectified voltage is used for direct battery charging without regulation.  And the 5 parallel LEDs are powered directly with only small series resistors.  All the wire connections are fragile.   For a retail price of $15, we do not expect it to be a very robust construction.

The battery pack seems no longer can hold charge.  We'll replace it with a small 480mAh LiPo pack (1.2 x 1.0 x 0.3"), that costs about $6 and is a little smaller than the NiMH pack (1.2x1.2x0.42") .   We install a 2mm JST PH 2.0 2-Pin connector.

We bring out the voltage after the bridge rectifiers to the outside, so we can monitor the crank generator output and potentially use it to power other devices, such as other chargers.   The diode to the Lipo isolates the battery to these wires, so it is relatively safe.

When unloaded, the crank generates about 5-8V at a reasonable crank rate.  It can peak over 10V if cranked really fast.  When it is loaded with battery, the voltages does not exceed 4.5V; after diode drop, the voltage on the battery is only about 3.8V, so it is safety for the battery .  The generator can supply enough power to sustain the radio, but not the LED light.

We also connect the output to a boost regulator, that generates 5V.  We use the 5V to charge a Bluetooth earphone.   The generator puts out 4.4V/45mA, about 200mW.   The rectified output is not very stable.  If we take the output from the battery side, it's better.  If we use it to charge a smartphone, the crank cannot keep up and the internal battery drains first.