Hi Rick,
No problem about questions, that's what a forum is for !.
The pinout details I got by searching for the datasheet of the RX-2 chip, which is used as the basis of many cheap RC toys from China. ( I'll post a copy and my notes when I am back on my own PC. )
My plan also was to replace the board, but when I got the car opened I decided I couldn't build circuitry as small as was needed, and why would I need to, as the only part I needed to replace is the processor ?.
So I got the pinouts from the datasheet, with the intention of seeing if I could replace the RX-2 with a 'drop in' tiny PICAXE. That's when I realised removing the original chip would be a Bad Move !. The RX-2 is not just an RC receiver, it's the boost convertor as well. It boosts the 1.4v from the tiny lithium cell to about 3.4v. I definitely couldn't build one that small !.
I've not measured the current draw of the steering coil. The transistors on the PCB must be rated big enough to drive it, so I'm not really bothered. Same with the motor. Also, I don't know what happens if I energise both directions at once, so I make sure not to !.
My biggest concern is the behaviour of the steering. The steering is done by energising the coil in opposite polarities, which then attracts one of two magnets attached to the steering bar, pulling the bar left or right accordingly. The RC chip just drives the steering bang-bang left or right, but I don't know how this will respond to PWM if I need to get 'smooth' steering.
Regarding photosensors, I've not looked yet. Whatever I choose I'm sure that some of the car chassis will need cutting out to make space. Your QRE1113 look like they will do the job, but I was thinking more along the line of 3mm 'LED style pkg' photodiodes and a couple of SMD LEDs.
Regarding using a 20X2, I'm not sure that is the best choice I could have made. I think I should maybe have used a 20M2, as it's got more PWM options. Now I might need to roll-my-own PWM, cos' I'm not changing the 20X2 after all that effort of getting in !.
I've re-installed the red tail light, and am going to add another, not because I like tail lights, but to use for diagnostics. ( My original intention was to use the ERF/URF for remote program and diagnostics, but there is no way I could fit it in the car. )
There is no proper code yet, just some routines to drive and turn. From these simple tests it looks like the car is going to be a bit of a challenge to control, it's steering is more than a bit erratic.
It's going to be a few more days before I can get back on this, how far have you got ?
Cheers,
Buzby