IR question

[Wibbly]

Hi, I am totally new here, and I should make it clear that I am total newbie when it comes to electronics, though I do build rc tanks etc which are quite complex beasts.

I have a problem and I am wondering whether anyone can shed some light on it.

RC tanks use an infra red emitter to fire a shot, the standard is 38khz modulated.

There are various systems on the market, ranging in price from £60-£250. I have several of each, but its the £60 one that is giving me a headache. The IR range of most systems is 25-30 meters. The range of the cheap board is about 3 meters.

The IR emitter is a Maplins YH70M, this is a standard issue IR emitter that most people use as it matches the Tamiya standard. In most systems it is a perfect replacement.

The only information that I can provide regarding the power to the emitter on the £65 board is that there is a surface mounted resistor in the circuit. With the resistor in place the voltage to the IR emitter is around 3.3v. If the resistor is bridged the voltage is around 7v.

7v will blow the emitter, and does not seem to increase the range before it does so.

With my limited knowledge of IR's, forward voltage etc, I am wondering whether there is a solution to this dilemma. After reading various articles on the web, I am making an assumption that the current to the emitter is low on amps and that it is this which is reducing the range.

Due to the microscopic design of this board, is there any way that I can increase the range? The only options that I have are to bridge the existing resistor (spec unknown but it does drop the volts by 50%) and fit another one inline to the emitter + leg. But I have no idea whether this would work, or even if it would, what the spec of the replacement resistor would need to be.

If anyone has a solution, I would really appreciate it.

Rob

 

[alec_t]

Just blindly replacing the resistor (assuming it's a current-limiting one in series with the LED) is asking for trouble. Any decent designer will have selected its value having regard to the maximum power handling ability of the IR LED. Without the LED spec and circuit voltage we can't advise re a replacement resistor. However, you might be able to double power output by duplicating the existing resistor/LED combination, providing whatever is switching the LED can handle the extra load safely.

 

[Wibbly]

Many thanks for the information, the issue of 'decent designer' is one that I can't comment on. He is someone who is new to the application of electronics to rc tanks, and although he has done wondrous things with the motor drives and programmability on the rest of the board, the IR is the weak point in the design. He is based in the far east and evades answering questions about the IR performance.

I will see if he will divulge more details about the feed to the emitter.