TP-Link TL-MR3420 V3 LEDE(OpenWRT fork) Custom Build

# This is just my old build log for TP-Link TL-MR3420 V3 LEDE (OpenWRT fork) custom build firmware.

Forums thread is here >>

I have some experience in openWRT platform and it’s hack-able features. I like and select to buy this 3420 router because this one is dead cheap and full featured, especially support with USB and 3G modem. Some alternative like 3020 and 703 are also cheap but very small and no feature like eth-switch and little gpio. But problem is TL-MR 3420 V3 is not supported by openWRT. So, I have to build my own custom firmware. I choose LEDE (the fork of openWRT) build.


1- First build attempt

I recently build TL-MR 3420 V3 firmware which was not yet supported by openwrt.
The board is very similar to V2 board but V3 is with new processor Qualcomm Atheros QCA9531.

My V3 Board specifics brief are as follows:
– Qualcomm Atheros QCA9531 650MHz
– 25Q32CS1G 4M
– Zentel A3S56D40FTP -G5 32 MiB

I started with TL-MR 3420 V2 profile.
“Target System” ⇒ “Atheros AR7xxx/AR9xxx”
“Target Profile” ⇒ “TP-LINK TL-MR3420 v2”

Build success without showing any error.
Then I tried to build from stock web based firmware upgrade but failed with error 18005 because of TP-Link genuine firmware check hash.
So, I tried with serial/tftp flash method and flashing “lede-ar71xx-generic-tl-mr3420-v2-squashfs-factory.bin” was successful :slight_smile: . LEDE is booted checked from serial console.

Error : But when I check from serial console, ifconfig shows only lo interface. No Eth/Wan nor WLAN is up.

Tried ./etc/init.d/network reload and show error.

root@lede:/# /etc/init.d/network reload
Failed to connect to the switch. Use the "list" command to see which switches are available.
[   56.975151] IPv6: ADDRCONF(NETDEV_UP): br-lan: link is not ready
'radio0' is disabled
'radio0' is disabled

Checked boot log and noticed errors.

[    0.115999] ar71xx: invalid MDIO id 1
[    1.414894] ag71xx ag71xx.0: invalid speed specified
[    1.420074] ag71xx: probe of ag71xx.0 failed with error -22
[    2.014883] ag71xx ag71xx.1: invalid speed specified
[    2.020033] ag71xx: probe of ag71xx.1 failed with error -22

Seem Switch/Eth driver is failed to load. How can I add network support for my board. If someone has experience on this series, also let me know.

Forum user @ahmadrasyidsalims point me out for the patch >>

I think you should be try :joy:


2- Second attempt

After loosing some hairs, some coffees + some nights, it was successfully booted and worked 🙂 .

TP-Link TL-MR-3420 V3 LEDE ( OpenWRT ) Custom Build

I re-patch this manually in current lede build.
In “menuconfig”, there is an option for “TL-MR3420 V3” profile. Good!!

This patch works basically,
– “lede-ar71xx-generic-tl-mr3420-v3-squashfs-factory.bin” was flashed and booted without any error
– LAN & WAN configured and works well now
– status LED works but other LED not
– USB storage is detected but 3G dongle not tested


  •  like other 4Mib flash router, space left in overlay/roots_data lefts only 492k
  • no space to install luci nor USB support package
  • – Seem extroot is solution but I want to use 3G dongle for usb.

Anyway, I have to rebuild firmware with removing some packages.
And any suggestion for which packages should be removed??

And some suggestion thankfully accepted 🙂 .

If you want to strip either PPPoE or IPv6, make sure you deselect the top LuCI entry as well, so you can deselect LuCI’s PPPoE support (and I think the same applies to IPv6).

you should be able to fit packages if you select them with “y” so they are integrated on build time. Build time integration compresses packages, 500k should be enough for luci and usb if integrated like that.

seem extroot is solution but I want to use 3G dongle for usb. >>

There are 3G/4G dongles with a microSD slot, you can do extroot there and be happy.
For example Huawei E3372h.
You can keep 3g/4g dongle tools in the extroot, as even if it does not detect the dongle’s modem it will detect the usb storage on it fine, so it will extroot and then detect the modem too.


3 – Third Attempt (Success)

Finally, tried to manage packages to fit in 4MiB. After removing some packages, custom build firmware worked fine with V-3 hardware.

For those who want to try, I build two versions. One for standalone and another for extroot support. Both versions removed ipv6 and pppoe supports.

1) This version supports
* Luci+bootstrap,
* 3G, usb, and
* ext-4 file system. Like @bobafetthotmail said, this version can detect SD card inside 3G-dongle.
* And I added mwan+luci-app-mwan3 for multi-wan support. Tested this also worked (Failed-over worked, load balancing is not tested)
Leaving about 104k space after flashed. Good point is you can still use extroot with this build (with ext-4, no vfat)


2) This version-2 is especially for extroot
* Luci+bootstrap,
* usb, and ext-4 and VFAT file system. This version can also detect SD card inside 3G-dongle.
* No mwan3 and no serial, no 3G dongle support. You can install whatever after extroot :slight_smile:
Leaving about 76k space after flashed.


By the way, Dear LEDE admin and developers, LEDE aimed for flash at least 8MiB, right!. But the problem is these cheap routers with USB support only have mostly 4MiB. Pls also consider for devices with 4M flash for some transition time.



thanks all,


DIY csCNC – 8 (PC softwares)

This is Just a follow  up post of my csCNC ver 1.0.  to warm up my hand after a long idle time in this blog.

After building hardware, I searched for available software options for running G-code, CAM jobs in PC. Options are the same as hardware. It must be free or opensource and also not a complex one. In short, I selected the following options.

SketchUp (Formerly from Google) 2D and 3D drawing software for drawing/cutting wood, plastic materials

Inkscape (open source vector drawing tool) for drawing vector image of bitmap image to vector converting

Eagle (Schematic and PCB designer, limitted but value worth free version available) my fav schematic and PCB tool

HeeksCNC (CAD/CAM software, opensource, but not free, for only £10, a bit confused 🙂 , source code is opensource and final application is not free. There is also trial version here. ) for converting drawing to G-code

OpenSCAM (opensource CAM simulation tool) for viewing and simulation g-code

Grbl Controller 3.0 (Gcode sender for Grbl) to send GCode to CNC machines

There are some important issue tips on using Grbl v0.9i with Grbl Controller 3.0.

  • At the first run, try to move Z first with axis control buttons. It will set feed rate first. If you jogs X,Y axis first, grbl will show “error:Undefined feed rate” error message. Grbl wiki said “Older Grbl versions had a default feed rate setting, which was illegal and was removed in Grbl v0.9.”.
  • Try soft-reset “$X” and try “$H” for homing. Home button from GUI is will not work after the first homing cycle is finished.


1# The first test was simple letter test. Draw some English and ျမန္မာ (this mean Myanmar ) in Inkscape. Save in “.dxf” format.



2# Convert “dxf” file  to G-code by HeeksCNC.


3# Simulated the G-code file and tool path with openSCAM.


4# After simulation result is satisfied, then run actual job with Grbl Controller + csCNC.


Small one, csCNC is moving !!!

DIY_CNC_TestRun (7)


The first result is not bad at all.

Ready for next test.

DIY csCNC – 7 (Spindle, Autolevel and Milling Test)

Spindle needs a lot of power and speed. But I have very limited resourced. First, I considered DIY style spindle but I cannot source right bearings and chuck or tool holder. So, I tried to use some small rotatory tools, PCB drill.

Some problems solved are:

  • CNC stopped with limit switch errors in a few minutes and after started milling. I checked limit switches and used a lot of methods such as filters, shield and cables but it didn’t work. I measured spindle motor’s power line (it is 12V DC ) and noticed some spikes. So, I replaced stocked 12V DC power supply with a good old quality power supply and the errors gone.
  • I know why everybody is talking about bed leveling. My first test did’t went well. I checked later that leveling error is about 2 mm from edge to edge of the bed 😦 .  Some said but I preferred stand alone program and this worked fine.

  • The only problem is I used WinXP and the program required .net ver 4.5 and this version didn’t support WinXP. So, I forked and recompiled with .net version 3.5 and Visual Studio Express 2012 to support WinXP.




Unfortunately, they cannot do the jobs well. Seem RPM is low and tool holders is vibrated a bit.  So, I tried small rotatory tool and it does the job for the first time.



I did some tests for 1 mil , 2 mils and 4 mils PCB tracks. The result is not so bad for the first run.


I don’t have proper CNC bits and waiting for the ordered bits for now. I will write a post about some final touch and tips and also about PC software soon.

DIY csCNC – 6 (Test running some jobs)

When Arduino meets PIC, csCNC was born. Before milling, I tested some jobs, text, drawing and also a sketch. See the video of csCNC drawing a sketch.

This is my DIY CNC machine which built for hobby and personal tool need. The designe is inspired by many CNC machines arround the net and used opensource Arduino based CNC controller name “grbl” and PIC based motor controller named “Linistepper”.   I use GRBL Controller 3.0 for PC software  and it worked well for the first run without tweaking too much.

After connecting everything, it is time to test some jobs.

  • Do you know who? 🙂
  • Ready to run

DIY_CNC_TestRun (2)

  • some test  run for text and Myanmar font

DIY_CNC_TestRun (1)


  • Drawn by CNC


Results are not bad for first movement test. Next step is milling test.



DIY csCNC – 5 (Connecting all, Grbl, Linistepper & Limit switches)

After pre-configuring grbl, time to assemble everything for the first test run. Here is my connection diagram for csCNC. Ref : grbl/wiki

My GRBL CNC Connection
My GRBL CNC Connection

1# assembled everything on board,

DIY_CNC_grbl_linisteppers (1)

2# Added face plates and Grbl reset, Feed/Hold, Cycle/Resume, Power switch, LEDs, USB port and also a back plate with DB-9 connectors for steppers, 12V terminal for spinner, fuse house, limit switches female jacks

DIY_CNC_grbl_linisteppers (3)


3# Installed simple 12V/3A power supply with 220V/12V transformer and 7805 regulator for 5V supply.

DIY_CNC_grbl_linisteppers (4)

4# installed limit switches, wiring everything.

DIY_CNC_LimitSwitches (6)
X axis Limit Switch
DIY_CNC_LimitSwitches (4)
Y axis Limit Switch
DIY_CNC_LimitSwitches (2)
Z axis Limit Switches

Done! ready for test jogs.

DIY_CNC_TestRun (2)
DIY cs CNC and Grbl + Linistepper Controllers

AT Command Tester Tool

This is hayes AT command test too for SIMCOM GSM/GPRS modules (tested with SIM90X, SIM300 and SIM800 believed also work).  This is very early alpha test release and use at your own risk.
I am not a programmer but I am an engineer who wrote codes for need.
Developed by Visual Studio Express 2010 and .NET 4.0 (For winXP compatibility)
Last year, I developped a GSM base project with SIM908 module. Mostly, GSM and GPRS modules works with Hayes AT commands. ( This type of module can be interfaced by UART and can controlled functions such as call, SMS and others many. Any UART terminal like Putty, Hyper Terminal can be used for this but typing many commands re is a boring tasks in development. So, I developed this application with my own need and share with you now.
AT Tester main screen
AT Tester main screen
Sample Connection diagram

Support the following AT commands.

  • AT AT command test
  • AT+CSQ GSM Signal strength
  • AT+CREG? Network Info
  • ATI Modem/Module informations
  • AT+GMR Hardware version
  • AT+GSV Firmware version
  • AT&F Modem reset
  • AT&W Configuration Save
  • AT+CPOWD=1 Power Off
  • ATD Voice Call
  • ATH HangUp Call
  • AT+CMGS SMS Sending
  • Also sending custom AT commands
  • receiving respond string from Modem and display in Hex format

How to run,

  1.  Connect PC and modules
  2.  Run ATester, choose COM port and speed, presses connect button.
  3.  Power up module. Will see “yyyyyyyyyy” like message when module is power up.
  4.  Press “AT” button, will see “OK” message in receive terminal is module is working.
  5.  Press “Signal” and “Network” buttons to check whether modem is associated with GSM network. Will show “+CSQ:22,0” for signal where 22 is signal quality (something liked bars in your handset). Higher number is indicated that strong in signal. For network, will show “+CREG: 1,1” “OK”. This means modem is associated with GSM network. Good to go.

Tips : Message reply with “OK” means command is corrected executed (not means it is worked). Message responds with “Error” indicates that there is error in command. Check details in AT command manual like this.

If these steps are fine, modem and software are working well. If something is wrong, consult with these ,

To be add

SMS Receiving Manny commands neet to add such as AT+CREG, AT+CGMI, AT+CGMM, AT+CGSN, AT+CGMR, AT+CIMI, AT+CPBR Decoding respond from modem (Some feedback string need to phrase for more understandable) GPS? Only for SIMXX8 modules GPRS support? Custom AT commands set editing and saving in config files for different modules.

I will add more commands and functions soon. Still tune.



#SaveMyanmar #saveBurma

Mostly, I posted tech articles in my blog. But for now, things are worse than ever. Relentless monsoon rains in Myanmar have triggered flash floods and landslides, destroying thousands of houses, farmland, bridges and roads – with fast-flowing waters hampering relief efforts.

In Myanmar, “46 people have died and more than 200,000 have been affected by the floods across the country”, an official at the Relief and Resettlement Department said.

Myanmar is a vast and poor country, where communications and infrastructure are already weak, prompting the United Nations to warn that a full picture of the scale of the disaster may not emerge for days.

Authorities have declared the four worst-hit areas in central and western Myanmar “national disaster-affected regions”.

So, I would like to request you and all around the world. Help us.

Here is my recommended payment gateway provider and charity for donation.


Update Donor list

MMR_0352_Flood_Affected_Tsps_A4_150729pm_v4 saveMyanmar


Thanks all,