I’ve almost finished my project with an Arduino Pro Mini + TFT display + OBDII UART board + self-made protection circuit. All works fine.
At the moment I’m using a crappy two wires (unshielded) cable to bring power from the 12V battery to input of the protection circuit. The power cable is around 1,2 meter. long
Today I was going to order a better cable (flame resistant, flexible, etc. etc.) but a doubt arises in my mind: it would be better to use a braid-shielded cable??? Could my small power line (around 155 mA at max consumption) interfere with some electronic devices of my motorcycle?
Additional question: in case I should use a shielded cable, how I should connect it? I mean:
positive wire to positive pole of the battery,
ground wire to ground pole of the battery,
shield braid to… to what? Again to the ground pole of the battery? :think:
So I will use an unshielded cable to power my Arduino. I don’t think that so small currents can create interfere with electronics devices of the vehicle. :think:
You should be worrying about the noise generated by the engine and charging system, and its effect on your device, not the other way around. In automobiles, protection circuitry capable of dealing with spikes of up to 600 V is often specified.
jremington:
You should be worrying about the noise generated by the engine and charging system, and its effect on your device, not the other way around. In automobiles, protection circuitry capable of dealing with spikes of up to 600 V is often specified.
Yeah, I know that. I've build a protection circuit with the help of people on the italian arduino forum. It works quite well. (Until now!)
Honestly, I have a second question about shielded cables. :oops:
Seems a stupid question but nobody talk about it:where I should wire the braid shield of a data cable???
My arduino is talking with the OBD board by using a (short) internet cat5 cable. This cable is shielded to protect signal from interferences but I think that the braid should be grounded somewhere, I’m wrong?
Grounds must be very carefully chosen in situations where large currents flow. For example, in an automobile you do NOT want to ground to battery negative, as there will be a significant voltage drop in the negative lead when things like starter motors are running.
Look up “star ground”. In cases where you are protecting measurement circuitry from external noise, the ground should be close as possible to a neutral point on the measuring device itself, and as far as possible from any current-carrying ground connections.