Unclear about fluctuating frequency when using NPN transistor

Question

I am trying to build a more complex circuit but am having trouble starting off. I am using tone() to generate a frequency on my 5V Arduino Nano on D3. If I measure the frequency directly at D3 to GND, I measure a consistent 123.15hz which is what I'm looking for. Now, If I use an NPN transistor(I have tried a S8050 and BC337) the frequency jumps between 107hz and 123hz when I measure at the emitter. I am using a 1k ohm resistor in between D3 and the base of the NPN.

Any suggestions would be greatly appreciated.

Thank you.

Answer 1

• 1st، as others have pointed out this problem, you have to change your wiring, connect the +5v wire to the collector (left side pin of the transistor in the schematic) & connect GND wire to the emitter (right side pin of the transistor)

• 2nd, in this schematic, you are measuring the current of transistor's output, not it's voltage. Remove the measuring instrument, replace it by a resistor as your load, then connect the measuring instrument to the load resistor in parallel (connect measuring instrument to both pins of the load resistor).

Answer 2

Your transistor seems to be connected backwards. What is that thing connected between the emitter and 5V, is that your measuring instrument? There needs to be a load between transistor and the power supply poles. Your set up just seems to be wrong.

Answer 3

Your NPN is reversed. The right way is collector on positive side and emitter negative. You also missed the loading resistor - usually its connected in collector side.

Answer 4

This was the correct way to wire and check the frequency.