If there is a pullup then your pulldown will have to be several times stronger to make sure that the floating value becomes a logic low. You now have an effective voltage divider with a pullup / pulldown configuration. Fighting against the configured on-chip pullup is going to mean that to output a high you're going to need many times the drive current you would normally need as you sink current into that low-value pulldown resistor.
Not sure what your threshold on the buzzer is but if the pullup is say 30 to 50K then to get a solid 10% default low on the pin you'd need a 3 to 5K resistor on the pulldown. That would be a 1.1 to 0.6mA load on the pin when it swings high. You're also burning 0.1mA when the pin floats since the voltage divider will always be present. That may or may not impact your design. Assuming I'm thinking of this correctly. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
