transistors
I've read some info on transistor about how it works. So let's say I savaged a receiver from a remote control car which generates 1.2v output from the receiver when signal is transmitted from the controller, would my circuit works? Still a beginner in electronics, forgive me for my bad circuit drawing.
EDIT – I think I may understand a bit now, if it's positioned the way on the left, would it work? Also, what are the difference between the left and the right?
I might be totally wrong here but my excuse is the question is very confusing. The circuit shown above is trying to pull the 2.52 V line down to ground through the 10R resistor and an NPN transistor. The original (pre-hacked circuit) you describe was it this? Forward and Reverse are mutually exclusive as are left and right. On the vehicles I've hacked into they usually have a spring loaded centre off action (joystick). Are you absolutely certain the pole of the switch went to ground (0v)?
You say when you touched R2 (140k) the remote worked sending a signal to the car. This sounds like you were acting as an input signal. By touching the input your body as an aerial picking up the local EM field, the 140K resistor being large enough to prevent the weak signal from being shorted out. That suggests to me that the control input needs to go HIGH rather than LOW and that the switch was actually connected to the positive rail. To test this hypothesis connect up the circuit below and let us know what happened.
The way it is described in the OP's circuit quotation will probably mean it doesn't work because the transistor emitter is connected only to the antenna and there is no mention of a pull-down resistor to properly bias the added transistor.
I'll also say this about the quote. The person writing it has no idea what he is doing or why it works:
Increasing the power output from the transmitter, as previously said in comments, is probably breaking laws on transmission levels especially if the power (or voltage?) is increased 15 times.
More likely to get a good increase in range (maybe double) is to improve the radio receiver in the car - this won't be illegal.
Best Answer
What you have drawn is an emitter follower circuit to power your load and, if your load was normally activated by about half a volt then your circuit will work.
However, it seems you want the full 12 volts to be applied to your load and this means voltage amplification. Try researching common emitter load control circuits.
I'll draw a picture in a while but I'm on android at the moment and that is impossible for me!
EDIT (simple analogy alert)
This is overly simple but hopefully demonstrates what happens (or what you need to do) when using a BJT to switch a load: -
In this circuit the BJT's emitter is grounded to 0V and any voltage applied to the base (provided it is above a certain threshold ~0.7V) will start to conduct a reasonable amount of current from collector to emitter. You can fully control small to medium loads when they are placed in the collector circuit.
Can you see that if you placed the load in the emitter AND your control voltage is only 1.2 volts, the voltage across the load cannot ever become 12V.