Teensy2 power consumption

[drfritznunkie]

Hello all-

I'm attempting to baseline the power usage of my setup before I start monkeying with sleeping and disabling stuff, and I'm getting really odd results. I'm using a T2 at 3v3 with the MCP supply from PJRC. I recently got a microUSB breakout board from Sparkfun, so now I'm feeding everything through that and using a cut miniUSB cable to talk to the T2.

I have breakouts from Adafruit for their 128x32 OLED and their Ultimate GPS attached that I've measured before with my craptacular Horrible Freight DMM. I remeasured them today and they're at the expected values: the display ~3-5mA, gps ~25mA.

But when I finally put my DMM on the T2, I got ~85mA?!

I'm stumped, and I've probably done something really stupid. Can any of you Teensy experts see anything wrong with my setup? I've attached a photo of the breadboarding.

Thanks,
Z

P.S. I had to create a new account to post this since the forum server doesn't appear to be sending out reset emails, perhaps the mailserver needs a swift kick in the ass?

 

[drfritznunkie]

Screwing around with this more, with the microUSB power removed, if I connect my DMM across the cut red miniUSB wire (i.e. the T2 is now being powered through its own miniUSB connection), I get 10mA, which is much better!

For a data only USB cable, should I cut the ground in the cable as well? Is that what I'm seeing?

Thanks,
Z

 

[PaulStoffregen]

Have you measured just the current to the OLED module?

OLED looks awesome, but it doesn't have a very good reputation for low power usage.

 

[drfritznunkie]

Sorry Paul, the email notifications aren't working for me, so I missed your reply.

I too was baffled, so I disconnected everything from the T2 and loaded your power sketch. I was able to replicate your findings, and it turns out that in my sketch, even though I'd disabled the UART explicitly, it wasn't getting shutdown, so I had to toss in a "Serial.end()", which wasn't obvious to me at the time.

Thank you for the feedback, I appreciate it!
Z