http://forums.leaflabs.com/topic.php?id=578 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:17:00 +0000 http://bbpress.org/?v=1.0.2 q http://forums.leaflabs.com/search.php http://forums.leaflabs.com/topic.php?id=578#post-3161 Sat, 18 Dec 2010 20:20:17 +0000 gbulmer 3161@http://forums.leaflabs.com/ <p>I should add ... </p> <p>If the question relates to your engine project, which I assume has a battery of much higher than 3.3V voltage, then I would leave series resistors in to protect the processor a little. A dead-short from, say, a 12V battery to a pin will quickly 'release the blue smoke' (fry it). Likely pins to get shorted are ones which are attached to wires, e.g. switches.</p> <p>The STM32F103xB documentation (Table 7) says the maximum injected current is 5mA, so it'd take a few K to protect a pin. </p> http://forums.leaflabs.com/topic.php?id=578#post-3159 Sat, 18 Dec 2010 16:21:43 +0000 soundcyst 3159@http://forums.leaflabs.com/ <p>the short answer is no, you shouldn't need additional resistors, though it may be safer to use them.</p> <p>you can also test to make sure your assumptions are correct.</p> <p>if you have the internal pullup's enabled, then a) the pin should be at 3.3v when nothing's connected. verify this with a multimeter if you have to, and b) connecting the pin to ground will not cause a direct short from vcc to gnd since there is a resistor in series. if you have an ammeter, you can use one to verify this, though you may wish to add a second, external resistor in series for your first measurement to make sure it behaves as expected. (i.e. the current measured should be (3.3v / (Rint + Rext))) </p> http://forums.leaflabs.com/topic.php?id=578#post-3155 Fri, 17 Dec 2010 20:12:43 +0000 gbulmer 3155@http://forums.leaflabs.com/ <p>Is there a chance that the switch might get shorted onto something?<br /> If you are <em>certain</em> there is no chance of misconnection, then there is little point protecting the pin. </p> http://forums.leaflabs.com/topic.php?id=578#post-3153 Fri, 17 Dec 2010 18:19:50 +0000 Silntknight 3153@http://forums.leaflabs.com/ <p>I have several switches as inputs for a project, but I am setting the inputs to use internal pull-up resistors so the switches ground the pin. Do I still need resistors (10K) in series with the switch or can I leave it as is? I don't think I need the resistors because I'm no longer sinking current into the pin. </p>