Board on 5V "bus", avoid powering others if USB is connected

Projects General Guidance
1

Hi,

I built a small sys where multiple arduino's are connected by "bus" cable, powering them from 5V supply via 5V PIN, communicating by PJON single-wire (4-wire setup, GND, 5V, RST, PJON). Megas, nanos, custom built sensors without on-board step-downs, so no other voltage is option.

When programming, external power is turned off, individual usb is connected to a board powers all other components. There was no problem yet, but it's not a good solution, removing 5v all the time from the programmed board is very unconvinient. Using diodes on each 5V PIN are causing under-voltage as it drops at least 0.7 volts. Any suggestion?

Thanks!

2

Don't hard wire them to the "bus". Use connectors.

3

I have a similar setup. My solution was to power each board through the USB connector. This keeps me from accidently connecting the computer while the individual Arduino is connected to the power bus. The only downside for me is I have both 5V (MEGA) and 3.3V (ESP-32) devices so I still have to have a ground connected on both.

4

Also Schottky diodes only drop about 0.3V vs. 0.7V for silicon, if that helps. You could also add on-board step-downs to your custom built sensors, and use a higher bus supply voltage, like 9V for example. It would also prevent voltage losses due to bus wire resistance as you get further away from the power supply.

5

You could add diodes and change your bus supply to 5.7V.

6

@anon57585045 Thanks, connectors are in use, the only problem is my design flaw as for testing I need the common ground and PJON connected, the connectors are 4-pin molex-likes... The master of PJON is on separated power supply with common ground. Raising the voltage seems the only reasonable way, ditch the beautiful 5V din-rail supplies... :slight_smile: I have 12v ones, but some of the devices are nanos and they can't handle it on long term, right? So 9V supply would be more ideal for those heatsink-less regulators.

@richesonp Good idea, would solve my needs, however I have ATmega328-based devices on custom pcb w/ various sensors, nano-like size and the space is very limited physically. :smiley:

@johnwasser Thanks, right, it could also work!

Thank you guys for your time!

7

Go ahead and leave everything on. build a USB cable that does not have 5V wired into it.