Robo RC

When my son wanted me to buy him a toy robot I asked him if he would like to build one with me instead, he was so interested so I told him that it will be a car robot with two motorized wheels controlled from the phone over bluetooth and he needs to sketch the design then build it using Lego blocks.

IMG_20150110_115340 IMG_20150110_115358 IMG_20150110_115409IMG_20150301_184414 IMG_20150301_184527 IMG_20150301_184516 IMG_20150301_184501 IMG_20150301_184432 device-2015-03-07-210547
 

While he was busy with the sketches I started looking for parts, so I went to eBay and found these wheels


They come in two speeds, I ordered the slower one since it has more torque.
These wheel will need something to control them since the Arduino micro-controller is not strong enough to drive them with enough current so wanted to build an H-bridge using transistors (which I have already) but I found  a module based on the L298 chip  which is very cheap and has a voltage regulator too, awesome.

Next was the bluetooth module, and I went for the HC-06 which is easy to use and also cheap.

Bluetooth HC06-2And finally is of course the Arduino board, I got the Arduino Pro Mini for its small size and low cost.

arduino_miniEven though I actually used the Arduino Uno for the development since it is much easier to upload the code and fix mistakes.

I got them all from eBay with the cheapest price I can get so some took about a month to arrive and I wasn’t in a hurry:

2x Car Robot Wheels: $6.00
L298N Dual H Bridge: $3.00
HC-06 Bluetooth Module: $4.00
Arduino Pro Mini: $2.60
40pin Dupont Wires: $1.50
Total = about $17

You will also need an Android Phone or tablet, any with Android 3.0 and up should do. Lego blocks or anything to use for the car body.

Here is a video we made showing how to use the app and explaining the car we built and its main parts:

To get the Andriod app click on the Google play icon below:
Android-app-on-google-play

for the Android source code click here
and for the Arduino code click here

Inside a fake ELM 327

I got myself on of those cheap Bluetooth OBDII dongles but it didn’t work in my car (2005 Dodge), it simply couldn’t detect the protocol which is SAE J1850 VPW used on most Chrysler/Dodge I believe before 2008. So I took it apart and as you can see in the picture it has two stacked circuit boards the one of top has a bluetooth chip (BEKEN BK3231Q) and a CAN protocol transceiver from NXP (TJA1040)

Fake ELM327

The flip side of the top board contains a CAN controller (MCP2515) from Microchip.

CAM controller MCP2515

However, and what is surprising is the bottom board which contains only voltage regulators for 5v and 3.3v and most of the OBD-II pins are not even connected!
OBD-II connections

Let’s compare  the connected pins to the pinout of the OBD-II connector in the image below

OBD2_pinout

So the 12v VCC (pin 16 in red) is connected and the two ground pins (pin 4 & 5 in gray). How about the different OBD2 protocols? let’s see:

  • CAN  (ISO15765) used pin 6 & 14 (green color) and they are connected.
  • ISO9141/14230 uses pin 7 & 15 (yellow color) and they are connected.
  • J1850 PWM uses pin 2 & 10 (blue color) and they are NOT connected.
  • J1850 VPW uses only pin 2 (blue color) and it is NOT connected.

So it is clear that this will not support any of the J1850 protocols which are used by most old American car makers (Chrysler/Dodge/Jeep, Ford, GM), luckily I think all new cars (2008+) are using the CAN protocol which is the newest among the others.


Update: Another fake OBD2 reader

I bought another Bluetooth OBD-2 reader that is slightly larger than the one I got before hoping it would have the parts needed to support all protocols and since the seller also claim it does. (Spoiler: I got a full refund).

obd2_01

Guess what? It is exactly the same as the other one, it didn’t work on both of my cars so I opened it up and unsurprisingly it has the same guts (same chips) in slightly different arrangement.

obd2_02 obd2_03 obd2_04
 

I think having full support is a little too costly even for the Chinese manufacturer, also don’t be fooled by some sellers on Amazon who sell the same exact models for $15+, increasing the price won’t make it work. I also won’t recommend using these basic devices in your car since they don’t have Bluetooth authentication! and any nearby hacker can connect to them and have full access to your car CAN bus and do whatever your car manufacturer has allowed on that bus. You might have heard about the recent car hacks like disabling the breaks and such.

So if you are looking for something that works with all protocols and also safe to use I would go with trusted brands that have been tested by many users, e.g. “OBDLink LX Bluetooth” which looks like the perfect solution, good quality build, support for all ODB2 protocols, sleep mode and has a security button that need to be pressed to allow Bluetooth pairing I have not used it though since it is a little expensive.