The regulators on cobra are capable of high voltages (over 12V) but, since FEZ Cobra draws a lot of power, the regulators will heat up especially when the TFT display is connected. Overheating will damage the regulators.
So this is what you should know:
If you are not connecting any display then you can get away with up to 9V. We still recommend 6V. You do not need regulated 6V so any transformer should work.
If you are connecting a TFT display then defiantly 6V only. You do not need regulated 6V so any transformer should work.
If you have REGULATED 5V and want to use that then solder a wire between VIN and 5V on the expansion header. Again, REGULATED 5V. Only use this option if you know what what I am talking about.
I have a bunch of ATX pc power supplies and would like to use one of them to provide power to the Cobra and sensors. Should I use the 3.3V or the 5V from the PSU seen that the Cobra operates at 3.3V?
I’m glad this thread was started, as I have a power-related question along these lines.
I want to power the Cobra w/TFT display from the 12v supply coming from a car’s OBD2 port. I’m using the Cobra enclosure w/proto board expansion, and I’m going to be connecting an OBD2 cable from the car’s OBD port to the Cobra via the D-Sub connector on the proto board.
Since your recommendation is to supply no more than 6v when using a display, what is the best way to drop the supplied 12v down to 6 to power the board? Is it just as simple as putting a regulator (like the LM317 available at SparkFun) on the proto board to drop it before it gets to the VIN pin? Or is it more complicated than that?
Sorry if this is a noob question. I come from a pure software background, so I just want to make sure I understand the correct way to drive the Cobra from a 12v source in a safe manner. The proto board will host an ELM327 + CAN tranceiver, and maybe a VS1053 breakout board + audio out jack in the future if there’s enough room left. I have the ELM circuit up and running on a breadboard and I’m making progress with the driver, but I’m currently powering the Cobra via USB only. When I get ready to move the circuit to the proto board, I would like to use the available 12v from the OBD port as long as I can do it safely.
I can’t conclusively tell you what parts you’ll need, but here’s some of the theories behind this.
To get 12v down to 5v that the Cobra uses, requires transformation (inside the regulator). The transformation produces heat. The larger the drop in voltage required, the more heat produced by that regulation. Add in higher current consumption requirement of the Cobra (when you add the LCD) then the regulator produces a lot more heat.
So whatever you do to drop your power down you need to be very careful that you make it thermally correct too - whack a big heatsink on it and be careful of where you mount it all !
Going by what you said, it looks like it is possible to do what I need to do as long as I make sure to properly deal with the heat dissipation issue. Thanks again!
I have requested someone to do this before. If you have FEZ Cobra connected to OBD2 and you can read the VIN number of the vehicle, I will give you 1000 points when you share a wiki page showing to do that.
For powering from OBD2, that is about 14V not 12V (when car is running) plus you will have all kind of noise from the vehicle so the best thing to have is a switching power supply. You can use something like this so you do not have to make your own power supply http://products.cui.com/getPDF.aspx?filename=V78XX-500+Series.pdf
I have seen the documentation and looked into it before. Seem very simple but I do not have time I was hoping someone will make this happen and will be generous enough to make a wiki page about the whole thing.
I created a CAN interface in about 2 minutes with my FEZ. Required only a CAN transceiver and two resistors to create a voltage divider for VREF. I have some code which successfully decodes NMEA2000 messages including PGNs.
Quite amazing how quickly you can get something up and running with FEZ. I’ll share as soon as I have the time
If you are connecting a TFT display then defiantly 6V only. You do not need regulated 6V so any transformer should work.
If you have REGULATED 5V and want to use that then solder a wire between VIN and 5V on the expansion header. Again, REGULATED 5V. Only use this option if you know what what I am talking about.[/quote]
Gus,
Regarding the regulators you linked to above…I ordered two of them; one that outputs 5v and another that outputs 6.5v. Which is the best to use for my needs? Again, I just need to power the Cobra + display + ELM327 using a 12v source.
According to your notes in 2 and 3 above, I think I should be able to use either regulator, but I just want to be 100% sure I’m using the right component before I wire everything up. Thanks again.
I was hoping someone will make this happen and will be generous enough to make a wiki page about the whole thing.