Model Rail IR Detection Help Needed!

[numbskull100]

I have built the circuit as per picture below.

I have used the components specified other than the IR LED and Sensor (both of which I have tested elsewhere and are functioning). The parts I have used instead are: **broken link removed** and Sensor **broken link removed**.

When the 12v power is on, the red LED is always on, regardless of the detection by the sensor.

I have tried the following...

Short the sensor - LED stays on.
Remove connection to base of the transistor (I assumed this at least would kill the light) - LED stays on.

Puzzled... Can anybody shed some light on this?

Thanks in advance....

**broken link removed**

 

[Mike_2545]

Are you sure you have L1 in the right way? It says "object blocking between here lights Red LED" You need IR light on the sensor to turn off the Red LED.

 

[numbskull100]

Yes, the LED works fine - tested with digi cam

 

[KeepItSimpleStupid]

Look at lower left hand corner pic with pink and yellow protrusions. The protrusions whould face each other.

 

[Brevor]

Check that T2 is installed correctly.

 

[3lectrokid]

Looking at that diagram R1 is 470 ohms. I haven't looked at the transistor but that value is generally used as an LED current limiter when the power supply is 5v. a 2.2k ohm resistor should be used at 12v. Without this change you will probably notice a shorter LED life. However I may be wrong about this?

Otherwise the schematic looks like it will work and so make sure all your connections are OK and if you have soldered wires directly to the transistor it is possible you broke the component if you left the soldering iron on the leads for too long