Trying to separate the motor from the Arduino

Hello,

I’ve already tried to create the ‘magic smoke’ with my Arduino, and all but succeeded. I did have to replace the main chip.

I’ve attached photos, Fig 1, and Fig 2, to show you what I’m trying to do.

I am hooking up a dc motor to an Aruino processor. The transistor you see in Fig 1. is a TIP 120 being used as a switch. I understand when 5 volts is applied to the base of the transistor (from pin 9 of the Arduino) current will flow and the motor will run. Here is my issue; the motor is hard wired to the circuit. I want the motor to be separate, meaning I want to plug it into the circuit with an RCA plug.

Here is my diagram of what I have done with the 12 volt DC adapter (Fig 2). I have spliced in a male RCA plug on the positive wire from the DC adapter, leading to the motor. The (+) wire from the adapter is connected to the outside mesh of the RCA connector and the center pin of the RCA plug carries on the (+) side of the motor. The (-) wire from the adapter goes straight to the motor. So if I short out the RCA plug the circuit is complete and the motor runs. I want to insert a female RCA plug into the circuit shown in Fig.1, so when I plug in my male RCA plug into it, the transistor essentially create the short and allows the motor to run.

I can’t figure out how to connect the female RCA plug into the circuit. Any help is greatly appreciated.

Thank you.

Fig 1.jpg

  1. BJTs and darlingtons such as the TIP120 are current controlled. You should never apply +5V direct to the base. Connect the Arduino output pin ()or other +5V source) to the base via a 1k resistor.

  2. You have the flyback diode connected in the wrong place. It should be in parallel with the motor, cathode to the +ve supply, anode to the TIP120 collector.

  3. What you have breadboarded is a TIP120 used as a low-side switch (it interrupts the negative connection to the motor), but the arrangement you describe using the RCA plug requires a high-side switch (interrupting the positive connection). To make a high side switch for +12V, you need a PNP transistor or P-channel mosfet, and a level shifting circuit. See http://i.stack.imgur.com/AyyEB.png for an example.

Thank you, you reminded me of something I read a while ago. Here is a new document I tweaking based on your suggestion. It is a word document that I have attached. Will this re-worked diagram work with the adapter cable I created? If so, where would I place the female RCA cable?

Thank you.

Mosfet.doc (53 KB)

I don't see any high-side switches in that document, although I do see a few mosfets used as low-side switches.

Hello,

I think I'm getting a better understanding of this. My issue is I believe, is that I wired the male RCA plug to the (+) positive wire of my adapter. If I had wired it to the (-) negative wire, then the circuit in my word document could work...

Sscreemberry:
I think I'm getting a better understanding of this. My issue is I believe, is that I wired the male RCA plug to the (+) positive wire of my adapter. If I had wired it to the (-) negative wire, then the circuit in my word document could work...

That is correct. Your existing circuit could work too.

My understanding of electronics is good enough to work my way through a schematic and understand what is going on. I'm not so good as to be able to create my own. I understand the word document schematic and I can switch my RCA cable over to the (-) wire to make it work. For my own study though, I will read up on high-side switches. I've already found a primer on it.

Thank you again.