Help, can't find my IR receiver window!

[Guy Lavoie]

If you're using a digital multimeter, then it might be a bit harder to give you a foolproof answer. I'm assuming that when you see "1", you are referring to high resistance (ie: you would also see a "1" with the probes not touching anything). If your meter has a "diode test" or similar function, then use that to test the junctions. Basically, you would want a transistor to show a resistance value when one probe is touching the base and then you try both the emitter and the collector with the other probe, but then to show an open circuit when you reverse the polarity of the probes and do the same tests over again. Finally, you want to measure an open circuit when testing from collector to emitter regardless of the probe polarity.

 

[electron]

I did select the diode testing mode, and 1 was displayed even if I didn't touch the collector/emitter. When I touch the emitter and collector with the probes, it still reads 1 as well. Do you still think I killed the transistor? I tried to keep the circuit as simple as possible, so not sure what else could be wrong.

 

[Guy Lavoie]

Like I said, any measurement between the emitter and collector should always show infinite resistance (a 1 in your case) regardless of probe polrity, so that test is correct.

Its your test between the base and the other two leads that concern me. With the probes one way, you should see a measurable resistance to both the collector and the emitter. When you reverse the probe polarity and test between the base and the other two leads again, you should now see a 1.

 

[electron]

I only see a measurable resistance between the base and emitter, so I guess the base<->collector is fried. I will try to find another one later today.

Do you know what kind these are, and if they are any good?
http://www.radioshack.com/product.asp?cata...t%5Fid=276-1617

Keep in mind that I need a range of 20-30 ft or so. Thanks Guy!

 

[smee]

A quote from the link that Guy originally posted:

The 2N3904 transistor can probably be substituted by any general purpose NPN switching transistor, like a 2N2222

The NPN part is the most important. The RS transistors you link to are NPN and will probably work.

If you go to RS, the transistors themselves should be labeled and you can probably read it through the packaging to see what they are.

I have not had particularly good luck buying bulk transistors from Radio Shack [1]. There have been multiple duds in the package.

If you want to buy a bunch of them, Mouser has 2N3904s for $0.05 a piece (or 100 for $4.40).

[1] in an emergency.

 

[electron]

I had the 15 pack in my hands last time I was there, and couldn't see any markings at all, which is why I didn't go with them. I'll get another single, and then just order the others from Mouser.

 

[smee]

I had the 15 pack in my hands last time I was there, and couldn't see any markings at all, which is why I didn't go with them. I'll get another single, and then just order the others from Mouser.

www.digikey.com and www.jameco.com are also options. I chose Mouser above because they looked to be the cheapest.

 

[Guy Lavoie]

The blown base to collector diagnostic would be consistent with the fact that the emitter and collector were reversed. In other words, if you would have had just the wrong resistor but the transistor would be have been oriented correctly, it is the base to emitter junction that would have gotten blown instead, from the excessive base current.

 

[jwilson56]

I too would stay away from the bulk package as I also have seen many duds. Bad enough trying to struggle with getting this to work with good parts let alone trying to do it with unknown parts.

As I said last night I would buy a small breadboard and plug the parts in and test it out. Then after you get it working build it up. If it doesn't work at least you know you melted it down with your soldering. Also use a click on heat sink between your solder connection and the device (one wire at a time). This will protect the parts from getting over heated.

John

 

[electron]

I bought a new soldering iron;
http://www.radioshack.com/product.asp?cata...ct%5Fid=64-2070

nothing fancy, but the kit came with a heatsink which they didn't sell seperately anymore. The tip is also much smaller.

I also bought a new transistor and new LED just in case.

 

[smee]

I bought a new soldering iron;
http://www.radioshack.com/product.asp?cata...ct%5Fid=64-2070

nothing fancy, but the kit came with a heatsink which they didn't sell seperately anymore. The tip is also much smaller.

I also bought a new transistor and new LED just in case.

But no solderless breadboard?

 

[electron]

they still didn't have them!

 

[electron]

Well I still had the same problem after rebuilding the circuit using all new parts, so this time I actually tried a new IR LED, connected directly to the IR terminals, and I could see it flash using my digital camera. This time I spread the pins out as much as I could, and was able to make much better joints thanks to the tips posted by some cocooners, and a new 25W soldering gun.

I also tested the old transistor again, and what do you know, it measures just fine once I removed it from the board, so there must have been a short circuit somewhere. I will be doing more testing tonight to see what exactly is wrong with the first LED (is it the mini jack connection, or is the LED fried, not sure), and then it is time to test the range of this thing. I will keep you guys posted, and thanks again for all the help!

 

[Rupp]

You know reading through this thread made me think "Man this is cool". Dan you and I seem to be on about the same level electronically and seeing all the help and walk-throughs made me - well - excited. It's hard to get a group of guys helping as you have here.

Guys keep up the excellent help and Dan keep us posted. All of us want-a-be EE's are following this closely.

 

[electron]

We are definitely in sync and on the same level, i.e. we are probably the only 2 people who have that car remote starter, and built it at the same time :lol:

I am hoping the range will be enough, but now that I redid the circuit several times, it looks so simple, and just the learning process alone was definitely exciting.