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I am trying to mod an RC car to be controlled by the Ardunio. After much reading on the net for tutorials I am pretty confused. I only have basic ardunio skills (hooking up leds/sensors, basic serial communication).

The is a chip in the middle of the RC cicruits which after research appears to control the car. It has 12 pins and i figure some of them must make the car go foward back etc. However I am not sure how to hook it up to the ardunio. I tried just connecting it to a digitial out with a resistor in between and touching each of the pins but none of them seemed to do anything.

Could someone please help me at least get the arduino to start the motor or something? Currently I am just at a deadend and have no idea what to do next.
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I don't think you connected the grounds, Dave.
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Quote
a chip in the middle of the RC cicruits which after research appears to control the car.
Care to publish your research for peer review?
Otherwise, we're just playing guessing games.
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okay maybe the easiest thing is to show a picture

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I don't think you connected the grounds, Dave.
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Any comments about the steering geometry of the vehicle (skid, differential, servo, passive one-way in reverse...), size of motors, where and what the motors are connected to, power source, observed oscilloscope traces of control signals... would be welcomed.
I'm guessing the "5W5RJ" marked components are also connected to the motors.
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Steering appears to be a servo with left/straight/centre positions only on front. On back is a drive motor which appears to only have one speed and can go forward and back.

The motors are sealed up in the plastic and i was hopefull i wouldn't need to break it open so I don't know what size they are.

For the thing with the 5WR5J both of the motors wires go into that before going to the other board. Both the blue wires to the motors come from the main board. I think are connected to the points labeled "m". The drive motor to the m in the bottom right and the servo motor for an "m" between the 2 metal plate things which is obsured a bit in the picture.

Power source is a 9.6v 750mAH battery.

"oscilloscope traces of control signals" - I don't know how to do this and don't have an oscilloscope.

Note the board also connected via a single black wire that had some headlights that flashed, but I cut it out because It was molded into the plastic top which I was getting rid of. The car still runs fine on remote control.
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You talk about "motor" and "motors" - are you including the steering servo in "motors"?
Is this a simple, encapsulated R/C type servo, or some sort of bare-bones device built into the toy?
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I was including the steering servo motor.

There is one drive motor and one steering servo motor. I think it is a simple encapsulated R/C type servo but im not that experienced with this sort of thing as you can tell.
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Destined - I'm willing to bet that the IC with the sticker on it marked "27" and "2345678901" is actually the RX2 half (16-pin DIP version) of the TX2/RX2 chipset pair. This is a very commonly used chipset in cheap R/C toys; a couple of things would help in making this a firm diagnosis:

1) A much more clear picture of the board (and peel that sticker off too - see what the writing is underneath)
2) A clear picture of the backside of the board, too (so we can see the circuit diagram).

As it is - I can't tell which end is "pin 1" (I can tell if that is a divot at the top of the chip in the pic or what - too much glare).

Likely the two heatsinks at the bottom are part of a 4 transistor or mosfet h-bridge, probably for the main driving motor; the four smaller transistors at the bottom right of the pic are likely for the steering "servo". All of this is just guesswork.

You do still have everything connected, right?

Anyhow - if it is the RX2 of the TX2/RX2 pair - you can find a good datasheet that will explain all about it here:

http://www.et.byu.edu/~bmazzeo/LTR/tech.phtml

But get us those pics, too!

BTW - based on your explanation of hookup - did you happen to connect the grounds (of the Arduino and the car) together? What you should be doing is following the diagram in the app-note on the datasheet (for reference implementation), and perhaps just using a jumper from the positive supply on the -car- to the -input- pins of the chip (follow the diagram on the datasheet - you do this wrong, and you could blow the chip, and who knows what else).

If none of this works out, you can always just rip out the board and hook up external driving circuitry (a couple of L298/L293 h-bridges would likely suffice - an L298 for the drive wheels, and an L293 for the steering would likely be best).

smiley
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Hi,
   A quick mod might want to try is to have a look at the 'turbo' channel, its seems to be an unused channel between the transmitter and receiver in most models using the TX2 (transmitter) RX2 (car) pair of chips. You could use it to operate lights, or a buzzer for a horn as a quick exercise to get familiar with the two chips - I haven't tried this myself, but if it is an unused channel its begging to be used for something.

Until you are familiar with the RX/TX2 I would suggest you don't connect the Arduino to them, I have no idea how much current would be drawn by the car and in the few cars I have opened most of the decoupling capacitors are labelled on the PCB but just not installed I suspect the same goes for flyback diodes. This is probably not a safe environment for to learn in.

One option that might be safer is to start at the transmitter, when I was trouble shooting my sons christmas present I used a jumper wire between the vin pin and the left,right,forwards and reverse pins of the transmitter chip to successfully operate the car. You could use transistors to replace the push buttons in the transmitter and operate them in software using the Arduino.

Have a look at my blog for some other ideas, its mostly Arduino for RC Race cars, but might be interesting to you http://rcarduino.blogspot.com/

Duane B
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Until you are familiar with the RX/TX2 I would suggest you don't connect the Arduino to them, I have no idea how much current would be drawn by the car and in the few cars I have opened most of the decoupling capacitors are labelled on the PCB but just not installed I suspect the same goes for flyback diodes. This is probably not a safe environment for to learn in.

I don't think any of this would really be an issue; if the car works fine without those parts, it's probably going to work fine with the Arduino in place of the RX2 chip. If there is much concern, just wire in the flyback diodes yourself if they don't exist (you're already hacking the car, what's a few more parts?).

As for the decoupling caps - you don't care about those. Ultimately, the point of the datasheet and the RX2 chip is to identify the pins for ground and the outputs. Once you have these verified and things working, you cut out/desolder the RX2 chip - it's no longer needed (nor are any decoupling caps it might or might not be using). The RX2 chip has a minimum output current of 4.5 mA at 4.0 VDC; I doubt that the maximum goes over 20 mA - but again, if this is a concern, find out what voltage is being used on those outputs (whatever the voltage is powering the chip on the VDD - pin 13), and use that to control the outputs - place a meter in between in current measurement mode, and find out. This is basic stuff here.

The only reason to use the transmitter would be if you want wireless open-loop control (not much use for most robot configurations) - or, you're so paranoid that you strap the transmitter (and batteries) to the car as well (workable, if awkward, I suppose - but then you are still wiring into the "other half" of the pair - what about any concerns there? I'm sure if the car was made cheap, so was the transmitter).

I wouldn't worry about direct connections to the outputs used by the RX2 chip - others have done this successfully if you search this forum (and it is being used by the class I linked before as well); but if there really are concerns, there are ways to address them before even hooking up the Arduino (if you are still worried - drop a 4N25/4N26 optocoupler between the Arduino outputs and the pads on the board, or a hex buffer IC, or a darlington array IC - or any number of other possible TTL buffering schemes).
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First I would like to thank everyone for the replies especially for a lost new poster like me.

To answer all the questions to the best of my ability
-The chip appears to be an RX-20 lC1081 (shown in picture).
-Everything is still connected except for the lights (i wanted them gone anyway). The car still runs fine by the radio control.
-I haven't connected the grounds (in fact i am not actually sure where the ground is on the car!)
-Yes the car is cheap as. I decieded to get something really cheap to hook up first. Then I could get a more expensive one which has multiple speeds and a servo which does more than just straight, full left, full right.

I am unsure what my next step should be. I just assumed (maybe somewhat stupidly) that I could just basically use the ardunio to switch on the forward/back/left/right/straight by connecting it to the right point on the board.

This page has a diagram of an RX2
http://www.jbprojects.net/projects/wifirobot/

Below are pictures of the front and back in the best quaility i can manage.


 
« Last Edit: January 13, 2012, 06:36:53 pm by Destined » Logged

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There's a ground on the chip. First - you need to read and understand the datasheet I linked; it has -all- of the information you need to get this working. Looking at the clearer photo of the chip you posted, pin 1 is on the left-hand side, bottom (notice the divot on the left hand side of the chip - that is IMPORTANT). Pins are counted on DIP ICs starting from pin 1, across the "bottom" (ref your pic), then back from the right-top pin to the left (so pin 16 is above pin 1, pin 15 is above pin 2, and so on - understand?).

Now - if you look at the datasheet, the table on page 4 - you will see that pin 2 is ground for the chip - that's your ground. Hook a black wire up to that (trace back from the pin on the underside - remember, pins are reversed! - and find a convenient solder point - or just solder to the black wire from the battery, it should be the same). Now, you want the power pin - that is pin 13 (reference the datasheet!); since pin 9 is on the top-right (again, referencing your picture), pin 13 will be above pin 4. That is the power pin for the chip (VDD). Again, find a convenient solder point nearby and solder a red wire to it.

Now - you should be able to use that red wire (from VDD), and -carefully- apply it, with the car turned on, to pins 10 and 11 (backward and forward respectively), and pins 6 and 7 (right and left respectively) - reference the diagram on page 7 of the datasheet, notice how those are connected in the example circuit. Be careful -not- to short that wire against any other pin, or any other part, or you may damage something! If you must, find solder points from those pins to the rest of the circuit, and bring out wires from those points, then short the wire ends together (this is safer).

Also note pin 12 - that is the "turbo" pin. Setting this pin "high" may enable some mode (typically "fast high speed" when the "forward" pin is brought high).

Note also that sometimes, these pins and such are "reversed" - so that forward is backwards, and right is left, etc. Not sure why, but the manufacturers do this.

Let us know how that goes. That should work. Note that this is all without using an Arduino. You may need to prop up the car to keep it from running away from you. If you get this working, then we can move on to the next step.
« Last Edit: January 13, 2012, 10:24:39 pm by cr0sh » Logged

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Again thank you for the help smiley I am starting to see where this is going.

I have attached an image to make sure I understand the pins before soldering.

It wouldn't be a good idea to solder on the top would it? just looks to be more space there than trying to solder exactly over the dot

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Hi,
   I have a quick question for cr0sh or anyone else who may know.

   I understand that the Hex buffer will take a TTL input and sink or source a larger current and voltage on the output side, is there a common IC that does the reverse i.e. takes a 6,7,8 or more volt input and converts it to TTL on the output side, with some protection in between ? If switching speed is a priority is an opto isolator my best option ?

Thanks
   Duane.
   
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Again thank you for the help smiley I am starting to see where this is going.

I have attached an image to make sure I understand the pins before soldering.

It wouldn't be a good idea to solder on the top would it? just looks to be more space there than trying to solder exactly over the dot



NO - This is wrong!

Look at your picture above. Pin 1 is at the BOTTOM-LEFT corner. Pin 8 is at the BOTTOM-RIGHT corner. Pin 9 is at the TOP-RIGHT corner. Pin 16 is at the TOP-LEFT corner.

Please re-draw your image - and post it again, so we can make sure you understand.

You do -not- want to solder onto the pins next to the chip -ever- because you may damage it from heat (especially if you are inexperienced - an experienced solderer can do this, but it is still risky).

Instead, look at the bottom of the board (and keep in mind that the pins are reversed when looking from the bottom - this is very important, and it is easy to make mistakes (even experts get confused!). Mark pin one or something with a marker if you have to. Ok - so looking at the bottom, where the chip is connected, you should be able to follow the trace out and away toward another pad (which may have a part in it) - solder to that pad; likely (especially for the pins that control functions of the car), that pad will be the leg of a resistor; the other leg of the resistor will be close by, and connected (likely) to the base of a transistor, as shown on page 7 of datasheet example. You want to solder to that resistor anyway to limit current to the transistor's base - whatever you do, don't solder to the base of the transistor, as you may end up drawing too much current and burn out either the resistor (or the Arduino's port).

That point should give you more room. If it still seems cramped - well, you gotta learn to solder somehow; if you don't want to risk it, then find some other "donor practice PCB" - and practice desoldering and soldering parts on until you are comfortable and make good solder joints. Also - here's a link (and the entire site is an excellent tutorial - especially if you are in the UK or Europe - if you are in the US, they use a slightly different method of denoting resistor values than we do here in the States - so keep that in mind if you decide to try any of the example circuits):

http://www.kpsec.freeuk.com/solder.htm

smiley
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