Hi
sorry for the n00b question! just got my JS220 and starting to play with it. First issue is helping a friend debug his IoT stack.
He has a Raspberry Pi 3B+ with a number of USB peripherals. One which is bus powered, and one which has it’s own external supply. The entire stack is being run from a 5V / 10A power supply which splits to a micro-USB for the Pi, and a barrel jack for the modem
he is experiencing constant “Under Voltage” and occasional instabilities - and my immediate thought was to get the JouleScope on the job as a good excuse to learn - but wondering in this case what you recommend the best setup to be? it would be interesting to log the voltage rails and current draw for the entire system, but then break it down to look at each component in isolation.
was looking at the USB front panel to help out, but I don’t think the JouleScope will supply enough current, and also when peripherals use USB for power and data, then that doesn’t help much either
cheers
Hi @ClubmanPlus850 and welcome to the Joulescope forum!
The Joulescope JS220 is rated to support up to 3A sustained. However, it is designed to support up to 4A sustained. As long as the target system (or subsystem) is under this amount, then the JS220 will be happy. If you do happen to exceed the JS220’s limits, it’s soft-fuse will engage. You will not damage your JS220, but the JS220 will cut power to the target.
The JS220 does not supply power, even with the USB front panel. The USB front panel (schematic) is simply an easier solution that having to cut a USB cable.
According to these benchmarks, the Raspberry Pi 3B+ draws 980 mA under full load. So, the question really is how much are those other USB peripherals consuming?
You could start by adding a powered USB hub so that the Pi does not have to supply all the USB peripherals. If that “fixes” the problem, then you have confirmed that it is a power / brown-out issue. A JS220 can then easily help you look at USB peripheral to help identify the power hogs. You can then replace them with more efficient alternatives or figure out to sequence activity to stay within the Pi’s USB power delivery limit.
Does this make sense and help?