Arduino Forum

Using Arduino => LEDs and Multiplexing => Topic started by: Natalya on May 20, 2019, 05:26 am

Title: Easy way to disconnect all ouputs mechanically?
Post by: Natalya on May 20, 2019, 05:26 am
- Pro Mini
- 4 outputs
- 1 input
- +5v and ground
- All this wired into a much larger circuit

I have a 3PDT switch that has the input, the +5v, and the ground on its poles.

If I turn the Arduino off using the 3PDT I want it to not send anymore signal on the output pins.

What actually happens:
The output pins are spliced into some other wires.  The "default" signals they're transmitting (from other hardware) somehow turn the Arduino on in a low power state and it kinda powers up and starts outputting the signals (varying speeds of on-off) on its 4 output pins which causes the Arduino-produced signals to get mixed in with the ones that were already on the lines and it causes funny behaviour.  The Arduino power indicator LED does NOT come on but one of the outputs was pin 13 which is also wired to an onboard LED and I see that one flashing even though the +5v and gnd to the Arduino are disconnected by the open 3PDT.

I could get like another 3PDT and a SPDT and just wire those in place, but I'm wondering if there's an easier way?  Could I use diodes on the output lines to stop the Arduino from being powered on in this weird low power state?  I do have a bunch of 1N4004 diodes on hand but I don't know if that's the right type.
Title: Re: Easy way to disconnect all ouputs mechanically?
Post by: PaulRB on May 20, 2019, 08:01 am
It's called "parasitic powering".

Why do you want to switch the Arduino off?

Please post a schematic.
Title: Re: Easy way to disconnect all ouputs mechanically?
Post by: Paul__B on May 20, 2019, 10:48 am
I have a 3PDT switch that has the input, the +5v, and the ground on its poles.
Why would you disconnect the ground line, and why would you even disconnect the input?

What is a double-throw switch doing if you only want to disconnect the Arduino which would require a single throw?

Does not the Arduino interfere with the other sources when it is switched on?  Why is this not a problem?

Could I use diodes on the output lines to stop the Arduino from being powered on in this weird low power state?  I do have a bunch of 1N4004 diodes on hand but I don't know if that's the right type.
You can use diodes wired anode to the Arduino, cathode to the external line so that the Arduino can only pull those lines HIGH but not LOW, given that the lines have pull-downs to do that already.

Yet another "XY problem (http://xyproblem.info/)".  :smiley-eek:
Title: Re: Easy way to disconnect all ouputs mechanically?
Post by: Natalya on May 20, 2019, 10:19 pm
Okay parasitic powering.  That is the problem it gets activated when I don't want it to be activated.  I can look for that now that I know what it is called.

I want the arduino to output absolutely nothing some of the time, which is why I put a 3PDT in series with its ground +5v and the signal in.

Why 3PDT instead of 3PST?  I had one on hand.  I could use single throw switches this isn't important.

I only switch the Arduino on when the other sources aren't outputting anything.    Instead of removing and reinserting the connections every time I had hoped to just press one or two buttons to stop the Arduino from outputting.