transistor trouble?

I am trying to trigger a transistor with my arduino BT board. Everything works great except for this last little issue.

I have a npn transistor(9016) set to power a relay. When I set a pin on the board HIGH to trigger the transistor it doesn't work. But if I manually set it high it works.

I really thought the HIGH signal would be strong enough to trigger the transistor...

Any suggestions?

[EDIT] Never mind. I used an opamp to increase the voltage. Works like a charm. It is to control a Glade Sense and Spray from an IRC channel. A complete write up on the project will be posted on my site in the next few days.

What is the complete transistor model number? A quick google suggests it could be an RF transistor (i.e. pretty unsuitable), but I may be wrong.

You need the device's HFE (gain); the current through the base is multiplied by this number to give the current through the transistor.

We would also need to know details of the relay, i.e. what current is needed to turn it on etc.

I answered my own question lol. I edited the first post; it explains everything.

I know you answered you own question but using an op-amp, an analogue circuit, to increase the voltage drive on a transistor used in the saturation mode (a digital circuit) is not a very good solution.

With the correct transistor and base resistor it should have worked. Even if you needed to boost the voltage to bigger than 5V a simple npn transistor should do.

I know it wasn’t the best method, but I wanted to use what I had and wanted it up and running.

I’ve always been kinda un-conventional, and using the op amp works; thats all I’m really after lol. I’m not in the “hardware” too much, I’m a programmer.

The write-up is now posted at and the video of it working is at

A hammer will put screws into a piece of wood, but someone who learns to use a screwdriver gets farther in the long run.

True, another one along the same lines is:-

A man who's only tool is a hammer, sees ever problem as a nail.

The write-up is now posted at

Thanks for writing up your work I am sure others will be intrested in it.

Can I make a plea for a real schematic, could anyone actually reproduce your circuit from the photograph that is figure 1.3. Sorry but I was a University Lecturer and old habits die hard. ;)

The schematics will be posted by 3a.m tomorrow morning. I have to work tonight. And I ran out of time last night.... er well this morning. I really need to start going to bed earlier....

As for the hammer and nail reference: Sure using a screwdriver would be easy, but bashing something with a hammer always was a bit more fun. I do know where you are coming from though. And I thank everyone for the suggestions.

The schematics are now up. I replaced Figure 1-3 with it.

No wonder you had issues with triggering the transistor. The relay coil should be connected between +5V and collector, rather than between emitter and ground as per your schematic.

If you move the relay accordingly and replace the op-amp with a 1k series resistor from the Arduino pin to the transistor base, you should be ok.

Thank you, it works without the overkill of an Op Amp. (feeling stupid) This is why I'm glad I joined a forum like this. I'll update the schematics and maybe use my arduino mini and make a permanent version.

As I complete more projects, I'll be sure to post a link here. The next project involves a nerf gun, flex sensors, and infrared tracking. All I need is the flex sensors.

All I need is the flex sensors.

Check this out as an alternative possibility to commercial flex sensors (which can be pricey).

Another option would be to pull some out of an old PowerGlove...


Just checked your blog and you have the collector and emitter symbols on your transistor swapped over. Collector is the one without the arrow and goes to relay and then +ve. The emitter is the one with the arrow and goes to ground.