Hi guys, Im new to Arduino, but ok with amateur eletronics. I have a project that im just starting and thought an arduino uno would bee a good controller.
Basically i have an auto gearbox with 3 solenoids in it, two of which change the gears, one of which locks up the torque converter (like a clutch)
These 3 solenoids run on 12v, and i was looking at using a TIP120 to switch the +12v going to the solenoids. I was having a play with a java circuit designer and noticed that if i switch 12v with the 5v i get from the arduino i only get around 4V from the emitter. I did have a play around and manage to get around 10.4 volts by putting a resistor between the base and collector and using a 42k pull up in the arduino.
With this setup i get around 150uA flowing back to the arduino. Is that a problem?
IS there a better way of doing this? I cant switch the ground, as thats the gearbox its self. Just worried 10.4 may not be enough?
I thought it would be simple to find a drawing on the web, not so, I can't believe how hard it was to find something. This page has a couple of examples
Might be an idea to share your circuit diagram.... you are using the transistor to control the connection to ground right? if you place it on the high side of the circuit - you'll run into problems.
Garynomad, that website was really helpfull, thanks
No im not controlling my ground, as the ground is the gearbox itself. I only have 3 wires going to the gearbox, and these provide +12v to the box to switch the solenoids.
what do we think of this? provides 11.44v to the solenoid.
If you are using an actual switch that's OK if not a bit back to front, but it's not OK if you are using an Arduino output.
If using an Arduino pin then you need a resistor from the pin to the NPN base (maybe 1k) and I would move the existing 1k resistor to GND and make it 10k.
Either way the FET should be a P-channel.
provides 11.44v to the solenoid.
Not sure why, there should be almost no voltage drop over the FET, .6v is way too much I think.
