Pull-Up Resistors
Invent-O-Doc
Posts: 768
I'm looking at hooking up SD cards to the prop. Although, I know it tends to work without pull-ups, I understand that we are supposed to use them. The schematics in the FSRW object indicate that 10K resistors should be used. I have a bunch of 100K resistor arrays (I know that would reduce the milliamperage). Do you think I would be ok using 100K?
Comments
Pull up resistor is max 100k-ohm.
Refer to 3.4.3.Bus Signal Line Load.
Somewhere is the distant past, I bought a lot of high value resitors in megaohm and hundred kilo-ohm range. I suspect I was thinking op-amps. Now I generally use nothing over 10K ohms.
Sure 100k may work as a pullup. But marginal values usually lead to odd problems. It won't hurt anything to try them, but you might find yourself wasting time with instabilities.
Do yourself a favor and stock pile some 10k ohms.
For a different reason, I rarely use anything under 220k ohms. Such resistors tend to draw too many milliamps from a micro-controller to be safe. And in other contexts, you may need 1/2watt or 1 watt resistors in that range.
At some point, usually too late, we all discover that we bought too many resistors and only use a few values. But at least they are very cheap.
between low current and high speed.
Remember that there is capacitance in both the propeller and sd card I/O pins.
100K resistors from a time constant ~10x longer than 10K resistors.
Russ
On the other lines, if you are not sharing the pins then no pullups are required (the prop drives one data line and the clock line, the card drives the other data line). If you really want to use pullups on the non-/CS lines, just be careful of your RC time constant.
Jonathan
Three in parallel work out to 33.3k, four in parallel work out to 12.5k, and five in parallel hit the mark at 10k.