If I’m reading your schematics correctly, you are using a MIC4680-ADJ for a power regulator. Reading their spec sheet gives me warm fuzzies that the unit would be capable of the electrical noise found in automotive environment.
http://www.micrel.com/_PDF/mic4680.pdf
I also read elsewhere that you shock test and heat/cool test your other units for the automotive field.
My question is: Has the Cobra II been tested in the automotive arena and is it on-label to plug it “directly” into the noisy 12V power systems of a car?
Justin
We use the fixed 5V version of that regulator IIRC. I belive it will work fine for you but no specific automotive testing has been done at this time.
Hello Justin
Did you made any tests using cobra in automotive?
I’m using cobra to read some automotive data (speed, RPM, etc) and pass those values to a tablet using usb cable. At labs i’m using a 12V rail from a PSU to power cobra, and everything works ok. When i connect the cobra to a car (and i’m using 12V from the car battery) i have strange behaviors like USB communications with tablet sometimes freezing. I have already spotted some problems that don’t exist if i use a stable PSU, so i’m guessing that powering cobra from 12V battery it is not good.
Is there any kind of filtering circuit that should be applyed betwen cobra and 12V bat?
Regards
@ geologic - The last login of Justin was more than 10 Month ago.
@ Reinhard Ostermeier - Sometimes users watch certain threads. You never know. Justin might get an email notification. Or somebody else who is watching this thread might have something to add.
Automotive power is a hellish nightmare to begin with. The main reasons for your issues are likely down to power transients on the 12V.
If the car engine is off then generally the supply is clean. With the engine running it looks like hell on a scope.
You need to handle filtering of the input to your board. A good ferrite inductor and suitable capacitors will clean it up for you. Have a look at the power input stage on a car audio system to get an idea of what’s needed.
I don’t have any recommended values off hand but you could start by looking at this device. I use this with most build these days that will be powered in a car or truck.
http://sg.element14.com/tdk/ach32c-104-t/filter-power-line-1206-3-5-200mhz/dp/1669279?Ntt=1669279
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I ordered 2 of those devices but they are so tiny that i destroyed them when soldering to my circuit.
I end up using a DC-DC converter found on ebay that have some nice input/output filtering caps, now my problems are gone.
Thanks Dave to point me the right direction , i’ll try those tiny devices later when i make a final PCB.
Regards