Do I need resistors with my transistor?

[Mat17]

I'm going to to use a 12V battery (with Solar Panel) to power an Arduino AND a 12V solenoid. I will use a transistor to switch the solenoid on after a digital output is sent from the Arduino.

The circuit will be similar to this raw design here, (minus the relay, and the motor is a solenoid).

Also, I have no idea about the 1K resistor or what value it should be. It was just a raw schematic from something else.

P.S. I also know I will need capacitors for the 7805l

 

[hevans1944]

.. The circuit will be similar to this raw design here, (minus the relay, and the motor is a solenoid). ...

If you intended to upload a schematic diagram or image, try again. It didn't work.

 

[Minder]

If driving a solenoid from an Arduino look at a Fet such as 2n7000.
If over 200ma load then a logic level power mosfet will work.
M.

 

[Mat17]

Sorry! Here is the schematic I was referring to.

https://www.electronicspoint.com/attachments/arduino-relay-motor-sw-gif.22622/

 

[BobK]

Yes, you need a resistor. The base emitter junction of a transistor is a diode. There is nothing to limit the current (except the internal resistance in the Arduino,)

Here is a resource that explains it all:

https://www.electronicspoint.com/resources/using-a-bipolar-transistor-to-turn-a-load-on-and-off.30/

Bob

 

[Minder]

That is the advantage of a Fet, It is voltage and not current driven.
M.

 

[Mat17]

Yes, you need a resistor. The base emitter junction of a transistor is a diode. There is nothing to limit the current (except the internal resistance in the Arduino,)

Here is a resource that explains it all:

https://www.electronicspoint.com/resources/using-a-bipolar-transistor-to-turn-a-load-on-and-off.30/

Bob

I love that page, it's just darn confusing! I still can't figure out my resistor value! Ugh!

 

[Arouse1973]

If you tell us the spec of the solenoid and what transistor your using I am sure we can work something out.
Cheers
Adam

 

[BobK]

For a saturated switch, my rule of thumb is base current 10% of collector current.

Collector current is what the solenoid draws. Call it Is.

Then it is simply Ohms law from there. The voltage across the base resistor is the voltage you apply to it -0.6V, the approximate Vbe.

So:

Ib = Is / 10

V = I * R

(Vin - 0.6) / Ib = R

Bob