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Topic: modding an RC car (Read 15 times) previous topic - next topic

Destined

#10
Jan 14, 2012, 12:30 am Last Edit: Jan 14, 2012, 12:36 am by Destined Reason: 1
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.


 

cr0sh

#11
Jan 14, 2012, 04:22 am Last Edit: Jan 14, 2012, 04:24 am by cr0sh Reason: 1
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.
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Destined

Again thank you for the help :) 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


DuaneB

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.
 

cr0sh


Again thank you for the help :) 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

:)
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

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