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Metro Mini - external power switch
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Please be positive and constructive with your questions and comments.

Metro Mini - external power switch

by copalfreak on Thu Mar 05, 2020 4:56 am

Limor Fried & KTOWN (or others that might be able to help),

Hi there!

I want to add a simple rocker switch for power so that I can leave the usb plugged in to the Metro Mini, but turn off
all the power to the board (and thus anything attached to it).

I have a USB with inline switch already, but that does not serve my purpose.
I am making a small 'control box' with 2 pots and a switch for power on/off.
Instead of having a power switch on an inline USB cable, and then a separate control with 2 pots on it, I want to make
just 1 box with all 3 in the same place.

Looking at the schematic for it, would it work if I put the switch between the USB Transceiver and the USB connector (Where I have the 2 red dots)?

CP2104_SW.jpg
CP2104_SW.jpg (63.19 KiB) Viewed 50 times


(U3G$1: after D+ and D- (3 & 4,) before 20329 on the Adafruit Version : https://cdn-learn.adafruit.com/assets/assets/000/045/231/original/adafruit_products_schem.png?1502682416 )

If there is a better way to do it than cutting traces, like maybe on the back where the 3 pads are for 5v and 3v, would you be so kind as to tell me?

Thank you!
P.S. - I found a pinout for a CO2104-GM chip from Silicon Labs, but not sure if it is the same one on the board.
CP2104.jpg
CP2104.jpg (77.03 KiB) Viewed 50 times

copalfreak
 
Posts: 33
Joined: Sun Feb 16, 2014 3:27 pm

Re: Metro Mini - external power switch

by dastels on Thu Mar 05, 2020 10:38 am

No. D-/D+ are the USB data lines.

You should put a switch on the VBUS line. The easiest way to do that is with an inline switch like you already have, but bundling it in the case.

You could use a microUSB breakout https://www.adafruit.com/product/1833 and plug https://www.adafruit.com/product/1390 and 4 wires (I suggest https://www.adafruit.com/product/3892 ... the Metro Mini doesn't use the ID pin on the USB connector... just connect the other 4 corresponding connections). Wire a switch inline on the VBUS wire.

Dave

dastels
 
Posts: 3819
Joined: Tue Oct 20, 2015 3:22 pm

Re: Metro Mini - external power switch

by copalfreak on Thu Mar 05, 2020 12:31 pm

Thank you for the reply dastels!

If I understand correctly, what you are suggesting is to get both the breakout (female) and the plug (male), and wire D-, D+, and GND together between them (probably ignoring ID since Metro doesn't use it), and then just put the rocker switch in-between the 5V connections in between the breakout and the plug). Then I just plug the male plug part into the Metro Mini, and the usb cable I am now using for power into the female (breakout board).
Is that correct?

Here is the case I made :
Case.jpg
Case.jpg (15.85 KiB) Viewed 37 times


As you can see, there is not much room in there.
I am using CAT5 for the wiring from this box to a variant of the 3d printed "PuzzleBox Bloom". Cat5 was not my first choice of course, but I wanted the 'color' of the outside wiring to be either a light blue or white to match colors with the project it's attached to. (base of lamp is same light blue as case, 'bloom' part is white.)
I looked all over for a (new) white 6-wire mouse or keyboard cable to cut up... No joy.

If my wiring description above is correct, I think using the breakout board and plug you suggested will work.
I might even be able to fit that additional circuitry in the bottom of the lamp part (where the Metro Mini is, not this 'control box' part).

I was really hoping to be able to just find a single trace to cut and solder the switch into.
(I am impatient, but no so impatient that I want to pay $50 shipping for $3 in parts. hehe)

I will wait on your reply.
If my thinking about the wiring is correct, I will order those parts and hopefully get this thing going soon.
Thanks!

copalfreak
 
Posts: 33
Joined: Sun Feb 16, 2014 3:27 pm

Re: Metro Mini - external power switch

by dastels on Thu Mar 05, 2020 12:37 pm

You are correct in your understanding. While you might be able to cleanly cut the power trace without damaging anything else, then cleaning away enough of the solder mask to be able to solder onto the trace pieces, then get wires soldered on.... it would sill be quite fragile (in my experience doing that sort of thing). Adding a switch on the usb cable will be much less error prone.

Dave

dastels
 
Posts: 3819
Joined: Tue Oct 20, 2015 3:22 pm

Re: Metro Mini - external power switch

by copalfreak on Thu Mar 05, 2020 5:18 pm

Thank you very much for you assistance!
Gonna place that order right now!

copalfreak
 
Posts: 33
Joined: Sun Feb 16, 2014 3:27 pm

Please be positive and constructive with your questions and comments.