transistor question with landtastic chip

[jeff262]

i just received my landtastic chip from http://www.rc-cam.com/ldtastic.htm. he says that the landing lights must be buffered by a transitor. how do i hook up the transitor, does it matter which one i get...radio shack has 5 different ones. i'm sorry if this is a really stupid question but i'm not sure what leg goes where! any info would help me alot since i know nothing about electronics!
thanks jeff

[ParkFlyer314]

buy the general purpose NPN transistors in the TO-92 case style ( the small ones). The output from yout landtastic chip will go to the base of the transistor. The Collector goes to the positive (+) side of your power supply. The Emitter goes to your LEDS. You will still need a current limiting resistor in series with the LED. The package the transistor comes in should show which pin is is which (emmiter, base, collector...)

[jperch]

Actually, This would work if you use a PNP type transistor. Instead, the emitter of the transistor should connect to ground, the collector to teh cathode of the LED, the anode of hte LED to the limiting resistor, then the other side of the resistor to the positive power lead. The base of the transistor would go to the PIC output through a limiting resistor.

Joe

[Marion]

Doesn't Mr CAM's web site show what transistor to use? When I visited there a few months back, it did. I believe the schematics I saw called for MOSFET type transistors -- 2N7000 or something like that.

Good luck

Marion

[jeff262]

out of the 3 you guys listed i still got the wrong one...story of my life. i have a MPF102 Feild effect transistor N-channel...whatever all of that means...will this one work? and yes i found that there is a schematic and he does use the 2n7000...should i just order that one from digi?
lost and confused as normal....jeff

[Mr.RC-CAM]

The published Landtastic schematic shows all the details. A very inexpensive MOSFET transistor is used to buffer the LED. The 2N7000 was chosen because it is a popular part and is good for several hundred mA's.

You can sub it with a typical NPN transistor (2N2222, PN2222, 2N3904, etc.). If you do this you will need to add a 2.2K ohm resistor in series with the NPN's Base lead. The Emitter would go to ground, and the Collector would feed the LED and its current limiting resistor.

RC-CAM