| ??? 05/16/05 11:37 Read: times |
#93487 - Mechanical switches need minimum current Responding to: ???'s previous message |
Michael said:
Using a pullup of 1K to 2.2K or so is a good value for when a mechanical switch is used directly at the port pins as an input. This size of resistor lets a few millamperes flow through the switch and keeps its contacts clean. Exactly! Mechanical switches need a minimum current to make them actually turn-on. This is often overlooked. The poorer the switch the more current is needed. It's a question of contact material. And if you have an expensive switch made of gold contacts 10kOhm pull-ups are enough. Another reason for keeping the pull-ups as low as possible, even if the choose of proper contact material would not demand this, is, that low pull-ups can tremendeously help to keep the according port line immune against hum and noise. A 1kOhm resistor can shunt interference to supply rails (and finally to ground) dozens of times better than the weak internal active pull-up of your micro! By the way, Marjan, by "weak" is meant, that very low pull-up current is flowing. So, a high ohmic pull-up is called "weak", whereas a low ohmic pull-up is called "strong". Kai |
| Topic | Author | Date |
| typical pull up for P3? | 01/01/70 00:00 | |
| 1K to 2.2K are good values | 01/01/70 00:00 | |
| Mechanical switches need minimum current | 01/01/70 00:00 | |
| ??? | 01/01/70 00:00 | |
| Dry loads | 01/01/70 00:00 | |
| P3 don't need pull ups. | 01/01/70 00:00 | |
| Misunderstanding! | 01/01/70 00:00 | |
| 1K is stronger not weaker. | 01/01/70 00:00 | |
| Switch Configuration !!! | 01/01/70 00:00 | |
| Thanx | 01/01/70 00:00 | |
| Why 1k? | 01/01/70 00:00 | |
because | 01/01/70 00:00 | |
| A Correction! | 01/01/70 00:00 |