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ljo , 06-03-2016, 08:24 AM

Hello,

I was looking at the beaglebone black schematic and I saw a lot of zero ohm resistors. What is the purpose of these resistors?

mairomaster , 06-03-2016, 08:52 AM

In general they give you lots of flexibility with the board. If you don't have the resistor, you will have the two nods connected simply by a track lets say. When you use a zero ohm resistor, the circuit works the same way, however you can do stuff like:

- Disconnect a particular block of the circuit simply by unsoldering the resistor. Otherwise you would need to cut the track, which is not very elegant and easy to fix - apart from that could be impossible if the track is on an internal layer of the board.
- Removing the resistor and connecting an amp meter in series, to measure the current flowing through that net (I believe that is potentially the idea of R6 above).
- Being able to split a net going to two different places, using a cross road with two zero ohm resistors. That way you can connect either of them, both of them or none.
- Being able to change the value of the resistor to something different than 0 ohm in case you decide you need to.

The 0 ohm resistors are mostly used with inital/debug versions of the boards since many things are unknown and need to be tested. Once a board is fully tested and ready for mass production, the number of 0 ohm resistors can be reduced.

ljo , 06-03-2016, 09:05 AM

thank you mairomaster for the answer.
Ok I understand. So In my case, it is not necessary for the board to work. I am doing my first PCB with the AM3358 TI SOC. I just want to make it work based on the beaglebone black PCB and the am3358 Starter kit PCB.