I’m trying to determine power consumption of my project. It’s a fairly straightforward circuit to download data over a serial interface, process it, and save it to an SD card. I’m using a Teensy 2.0 with the pjrc.com microSD adapter. Unfortunately, it’s going to be a few weeks until I can test it in action. On the bench, I can power everything up and initialize the SD card, and measure the power consumption while I do that (~55 mA at 5v). Will actually writing to the SD card make a significant difference, or can I be reasonably confident in that figure?
Sdcards can take between 5-40mA, based on type and on what they do actually (init, read, write, idle..). Take as a worst case 40mA. The current consumption has peeks, so provide a good decoupling near the sdcard's socket. P.
Wow--up to 40 mA is a surprise. Definitely will need to test it out in action.
SanDisk datasheet states their microSD card read/write could use 100ma. :(
Is that the SD card you have?
Zack_Johnston: Is that the SD card you have?
If you are aiming that at me, the answer is yes. That is what I have. But mine is on an ethernet shield, and it has its own 3.3v regulator for the onboard stuff.
Ok...Thanks. I am using the same one. Wow 100ma? That is surprising!
Page 2-1 has the specs for read and write. http://media.digikey.com/pdf/Data%20Sheets/M-Systems%20Inc%20PDFs/SD%20Card%20Prod%20Family%20OEM%20Manual.pdf
Sounds like a job for the min/max mode on the DMM, and maybe checking it out with a couple of different uSD cards.
You won't get the answer with a DMM. The max current occurs while flash is being programmed. This is a brief interval and occurs at random times determined by the SD card's flash controller. A DMM is too slow to measure this.
80 ma is common for consumer uSD cards.
Plan on 100 ma. Some cards hit 150 ma peak for 10 us so good bypass caps are needed.
Some older SDHC cards require 200 ma for write.
My issue is to choose a coin cell battery capacity that will last for 10 hours of continuous writing to an SD card of 4 integer values 120 times per second. Do I assume correctly that the 100-150 ma peak values are momentary? If so what might be the average ma expended under my conditions? I know that it depends on my setup and other variables, but a rough guess would help me pick a battery. Thanks.