Resistor positioning for DIN

[m00dawg]

Perhaps a silly question, but I am curious as to if the order of components when using a pull-up resistor matters for the tactile switches and knobs? In other words, does it matter if the resistor is between the shift-register's pin and the component or not? Reason I ask is that having to follow such a rule would, of course, have an impact on how I place my components on my control surface boards.

My intuition is that it doesn't matter, but I thought better to ask than be sorry :)

[nILS]

There is, of course, an impact on various properties of the circuit. None of them are in any way relevant for this application though :) So your answer is: No, it doesn't matter.

Then again, having the pullups close to the SR is usually neat, since you have all the pins and +5V there anyways. If you use res-nets it's pretty much impossible to route it any nicer/more compact than that.

[m00dawg]

I looked at resnets, but man for SMD, they looked rather challenging. Valid point, though, that would simplify things for me by using them. I am using SMD resistors at least, but they are in convenient places as opposed to being close to the chip. Trying to get around the wiring complexity by using GND and PWR planes.

[m00dawg]

Hmm well actually these might work. They are the same pitch at the SMD SR chips I am using and appear to have troughs for each pin so that might work. Anyone use these with some results to share?

[nebula]

For my sequencer project I'm using SOIC shift registers, and 5-resistor (6-pin) thru-hole SIP networks as pullups. (Also I used thru-hole bypass caps). On one side of the SR there is an unused resistor in the network, and on the other the 5th resistor is used as the pull-up on the SR chain signal. I found myself occasionally connecting both the pull-up and the button input directly to the IC pin - the order will make no difference.

I chose the bussed thru-hole resistor networks mainly because they're really cheap.

I don't know if it's any help or not, but I'm attaching a couple of pics that sort of illustrate how I did it... at the very least it may give you some ideas. I think you can click the thumbnails to make bigger images

The first pic shows a basic DIN SR with pull-ups right by the IC.

The second shows a DIN SR where I didn't have room for the pull-ups. This was the last DIN in my chain, so not all pins are used.

The third shows a DIN SR where there were other components and traces in my way, so I had to move the resistor network to another part of the world.

Edited October 18, 2011 by nebula

[m00dawg]

Thanks for all the help (both Nebula and nILS). Wish they had SMD resistor networks like the through hole ones you provided as an example. The only ones I found were basically individual resistors in a single package, which actually made it more difficult to route things to my buttons.

Thought about using the through-holes as you have. Still debating on that actually. So far, the individual SMD resistors don't seem to be causing any issues, but I'm not done routing everything yet. This board has 3 595's and 5 165's (it's for the OSC and ENV sections of my control surface).

[m00dawg]

Tried using through hole resnets and actually they helped far more than I thought they did. I have them more or less next to the SMD chip and it's nice because I can still run traces through the gaps between the holes and can use any layer to connect to the buttons without having to make a bunch of vias on my own. Good suggestion! I'm going to try it on my other boards as well as I am using individual resistors on them and like to keep the parts more or less the same across them.

Should be done with the board that sparked this question soon (maybe today)! Thanks again for everyone's help!