Hello,
I am new to electronics, and to this forum...
If anyone could help me, it would be very appreciated.
I can't seem to figure out my problem.
I am trying to get my Arduino to automatically start my car for me at 5:00am.
I have an extra remote for my remote start, and have soldered two wires to the button that starts the car. (If you touch the two wires together, it acts as if the button was pushed.) The remote has its own battery, which says 23A, 12V.
I have been trying to get this to work with a transistor (TIP120 & P2N2222A), but I have been unsuccessful. I wanted to use a battery for the Arduino, and wanted the battery to last for a while. Therefore, I was trying to avoid using a relay.
Is it possible to use a transistor? I have seen in other projects on the web, that people have used a transistor to turn on motors, for example... And I thought that I could use it for this????
Am I thinking about this the wrong way?
Thank you,
Jason
My first question would be, is that button closing the circuit to ground or to positive voltage? that may end up being an issue. I personally would use an opto-isolator with a darlington pair. the led side if the opto would be controlled by your microcontroller. the darlington pair would drive the button side. this would save you considerable amounts of energy over a mosfet or relay.
jasonandkids:
I wanted to use a battery for the Arduino, and wanted the battery to last for a while. Therefore, I was trying to avoid using a relay.
If all you're doing is triggering a switch, the current you're switching will be tiny and it would only need to be switched briefly, so power drain when you do this shouldn't be an issue. More important IMO is how the Arduino itself will be powered. Is it going to be in the car and powered from the car battery? If so you need to be aware that it'll add about 50mA continuous drain on the battery and that's enough to be an issue if it's going to be left running for days. If it's going to be powered from somewhere else then you still need to figure out how it's going to be powered.
SargentSeven:
My first question would be, is that button closing the circuit to ground or to positive voltage? that may end up being an issue. I personally would use an opto-isolator with a Darlington pair. the led side if the opto would be controlled by your microcontroller. the Darlington pair would drive the button side. this would save you considerable amounts of energy over a mosfet or relay.
Few things wrong there.
If a transistor is not triggering the remote correctly, it is most likely due to being connected with the wrong polarity, as you first suggest.
The only other possibility, is that the saturation voltage of the transistor is too high, but that is unlikely in a 12V circuit. If he were to describe - in accurate detail - how the transistor is connected and what base resistor he has used, we might be more helpful.
Why a Darlington pair is inappropriate is that it has a much higher saturation voltage (voltage drop) than a single transistor. Again, this would be less of a concern from a 12V supply, than from a 3.5V supply where it would be quite useless.
Lastly, a MOSFET - of the "Logic level" variety to actually switch at Arduino voltages - would be the most energy-efficient as it takes zero current to drive, and could potentially have the lowest saturation voltage.
A correctly-wired transistor is in general, the most appropriate approach.