Can you turn old RC car and control it with phone?
Yes you can and I will show you how to do it. This is my first instructable so if something isn't clear how I did it ask in comments and I'm sorry for bad grammar.
My RC car have RX-2B as controller but even if you got some other chip it's pretty easy to look in datasheets and connect it right because we will only use H-bridge on PCB. I will use NodeMCU as controller and connect it to H-bridge on PCB but you can use any microcontroller you have and just add bluetooth module or esp8266 for Wifi.
1. Old or some cheap RC car
4. 4 AA battery and 1 9V battery
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Step 1: PCB
RX-2B is used with TX-2B. TX is transmitter and RX is receiver. In datasheets you can see pins of RX-2B and how to connected it. My RX-2B was connected similar to the datasheet but without turbo pin connected.
We need only 4 pins to control 2 H-bridges(forward,backward,right,left). You have to find that pins on PCB and then follow lines to the resistors and solder wires to that resistors. It's a good thing to destroy lines from resistors to the pins so no current is going in RX-2B or you can completely remove RX and only left H-bridges on PCB
Step 2: NodeMCU
Now you have to connect wires that you solder to the NodeMCU and connect ground of PCB to ground of NodeMCU.
I connected D1-forward, D2-backward, D5-left, D6-right.
I added 9v battery just to power NodeMCU (via Vin) because 4 AA battery does not have enough power to power motors and nodeMCU; I added switch for turning NodeMCU on and off; I removed small spring from first motor that was returning wheels in natural position(optional).
Step 3: Code
We will connect to wifi and anybody that is connected on that wifi can write IP address of NodeMCU in explorer and by adding something after IP address we can trigger some action on the board(eg. 192.168.5.5/high that will set D1 HIGH and motor will start to spin forward). But that is bad way to control car so I made app that when some button is pressed it write address and some word for us.
Step 4: Conclusion
It's fun little project that works but there are ways to improve it:
1. 4 AA battery are draining fast so a better solution would be rechargeable battery
2. WiFi isn't a best way to drive car, Bluetooth would be better
3. maybe 3D print or make some enclosure for car