Pro Mini 3.3V relay control [Solved]

Using Arduino General Electronics
1

Solved it. Using an NPN transistor I needed the load to be connected to the collector and I had it connected to the emitter. It was right on my schematic, just user error.

I have a project that I need to control a relay in order to switch high voltage. I have a 5V relay and I'm using a 2n3904 to control the 5 volts to turn the relay on and off but it's not working. I can hear the relay begin to move but it does not latch and the contacts don't touch. If I apply 5 volts directly to the relay it latches no problem, but when controlled by the transistor it doesn't work. Here is the schematic

(the PZT3904 is the surface mount version of the 2n3904, I'm using the through hole part for prototyping). I have tried with a 2.2K resistor, a 1K resistor, and lower, but it has made no difference. I've done the math and those values should allow enough current to flow through the coil of the relay, it only requires 80mA. If it helps theres about a 2-2.5 volt drop across the transistor when its "on".

Has anyone done something similar or have any ideas why this isn't working?

Thanks

2

Use a 330 ohm resistor.

Did you remember to set the relevant Pro Mini pin as an output?

3

I found my issue, the transistor was placed correctly in the schematic, but not in the prototype. I had it placed up stream of the relay and not downstream. All is well now, thank you!