dmf3k
Newbie
Let me apologize up front, I was an English major in college and have no business fooling around with some of these concepts, but as a lifelong tinkerer, I find myself once again asking the experts to bail me out.
After locking my keys in my 1990 Ford Bronco II, I decided I was going to create an RFID Power Unlock mechanism. I was able to get the Arduino and RFID module to work like a dream. My problem now is installing it into the car. I have a pretty good grasp of how the power locking mechanism works. I'm really just asking for help with the safety of this circuit, particularly how these resistors and other components will hold up under the load that will be put on them.
Let me give you some background on the project and then I have three safety questions I would appreciate any help with. Here is the circuit for the vehicles power locks.
A note on how this circuit functions. The power lock switches automatically toggle the always hot and ground contacts so that the circuit sends current through the motor in one direction and grounds the other or sends current down the other wire and grounds the first. This either locks or unlocks the doors. I have spliced the wire above the motor and tested sending current to the motor through the PNK/BLK wire but if the wire is still connected then not enough current reaches the motor and it does not fully unlock. If the wire is severed and I put power through it directly to the motor, it fully unlocks. This tells me that I have to stop current from going back to the switches if I want this to project to work. But, seeing that I would also like the switches to operate as normal, I will need to rig up a way for the current to flow in both directions under normal circumstances, but when I want the Arduino to unlock the door, I will need to cut current from going away from the motor. This complication has led me deep into learning about and experimenting with MOSFETs and this is what I've come up with:
The RED and BLK wires going into my project box are always hot and ground. When current flows towards the motor through the PNK/BLK wire, it will unlock the car door. So there are three situations I need to permit:
1. Current flows from the switch (i.e. "down" PNK/BLK) the N-channel MOSFET 4 is pulled down so it is off, but P-channel MOSFET 5 is pulled down so it is on, allowing current to pass and the door to unlock.
2. Current flows from the motor to the switch (i.e. "up" PNK/BLK). M4 is pulled up and turns on while M5 turns off. Current also flows to P-Channel M2 which is pulled up so off.
3. The Arduino turns Pin 3 HIGH. N-channel M1 is switch on, dropping current to M2, turning it on. Current runs to the motor. Simultaneously, M3 is switched on turning, diverting current from M4, turning it off, which effectively blocks current from flowing "up" PNK/BLK.
In theory, I'm comfortable with how this works. And with most DIY projects, I've already come to terms with the idea that I'm not saving money here but I am learning a great deal and that is, of course, invaluable. I'm really not so concerned if I fry an Arduino in the pursuit, but I would like to avoid blowing up my car.
All that being said, here are my three safety concerns:
1. I have your basic Arduino hobbyist resistors. I'm looking to use them to pull up/down on the main power line running from the car battery. The Motor pulls 30A at 13V which is a lot more power than these resistors can handle. With the way they are currently set up, will these resistors actually see that much power? Is the current set up inadvisable (read: dangerous?)
2. Same as question 1 but this time for the MOSFETs. My P-Channel (IRF4905) are rated for -42A and my N-Channel (8A28RL) are rated for 30A. It seems (to me) from the specs they can hold up, but something about the small prongs on the transistor itself still make me nervous.
3. I am worried that M2 won't function the way I want it to. When I unlock the door from the door switch (current runs from the motor "up" PNK/BLK) it will run to M2. If M2 does not stop current from crossing it will then meet with current running "down" the always hot RED. Will these two currents create some sort of dangerous spike in power?
After locking my keys in my 1990 Ford Bronco II, I decided I was going to create an RFID Power Unlock mechanism. I was able to get the Arduino and RFID module to work like a dream. My problem now is installing it into the car. I have a pretty good grasp of how the power locking mechanism works. I'm really just asking for help with the safety of this circuit, particularly how these resistors and other components will hold up under the load that will be put on them.
Let me give you some background on the project and then I have three safety questions I would appreciate any help with. Here is the circuit for the vehicles power locks.
A note on how this circuit functions. The power lock switches automatically toggle the always hot and ground contacts so that the circuit sends current through the motor in one direction and grounds the other or sends current down the other wire and grounds the first. This either locks or unlocks the doors. I have spliced the wire above the motor and tested sending current to the motor through the PNK/BLK wire but if the wire is still connected then not enough current reaches the motor and it does not fully unlock. If the wire is severed and I put power through it directly to the motor, it fully unlocks. This tells me that I have to stop current from going back to the switches if I want this to project to work. But, seeing that I would also like the switches to operate as normal, I will need to rig up a way for the current to flow in both directions under normal circumstances, but when I want the Arduino to unlock the door, I will need to cut current from going away from the motor. This complication has led me deep into learning about and experimenting with MOSFETs and this is what I've come up with:
The RED and BLK wires going into my project box are always hot and ground. When current flows towards the motor through the PNK/BLK wire, it will unlock the car door. So there are three situations I need to permit:
1. Current flows from the switch (i.e. "down" PNK/BLK) the N-channel MOSFET 4 is pulled down so it is off, but P-channel MOSFET 5 is pulled down so it is on, allowing current to pass and the door to unlock.
2. Current flows from the motor to the switch (i.e. "up" PNK/BLK). M4 is pulled up and turns on while M5 turns off. Current also flows to P-Channel M2 which is pulled up so off.
3. The Arduino turns Pin 3 HIGH. N-channel M1 is switch on, dropping current to M2, turning it on. Current runs to the motor. Simultaneously, M3 is switched on turning, diverting current from M4, turning it off, which effectively blocks current from flowing "up" PNK/BLK.
In theory, I'm comfortable with how this works. And with most DIY projects, I've already come to terms with the idea that I'm not saving money here but I am learning a great deal and that is, of course, invaluable. I'm really not so concerned if I fry an Arduino in the pursuit, but I would like to avoid blowing up my car.
All that being said, here are my three safety concerns:
1. I have your basic Arduino hobbyist resistors. I'm looking to use them to pull up/down on the main power line running from the car battery. The Motor pulls 30A at 13V which is a lot more power than these resistors can handle. With the way they are currently set up, will these resistors actually see that much power? Is the current set up inadvisable (read: dangerous?)
2. Same as question 1 but this time for the MOSFETs. My P-Channel (IRF4905) are rated for -42A and my N-Channel (8A28RL) are rated for 30A. It seems (to me) from the specs they can hold up, but something about the small prongs on the transistor itself still make me nervous.
3. I am worried that M2 won't function the way I want it to. When I unlock the door from the door switch (current runs from the motor "up" PNK/BLK) it will run to M2. If M2 does not stop current from crossing it will then meet with current running "down" the always hot RED. Will these two currents create some sort of dangerous spike in power?
