| ??? 09/03/09 10:10 Modified: 09/03/09 10:12 Read: times |
#168721 - Use a base-emitter resistor Responding to: ???'s previous message |
I assume that you have the PIR output connected to the BC547 base via a 10k resistor or so. And the collector to Vcc with another 10k resistor which is effectively your 8051's necessary pull-up.
The transistor is probably switching with a relatively low voltage from the PIR. So use a base-emitter resistor of about 1k. Better still calculate the resistors properly. You do not want the BC547 to turn on until you have at least 3V at the PIR output. The base-emitter voltage Vbe will be about 600mV at Ic of 500uA. Again read the data sheet. David. |
| Topic | Author | Date |
| Is pull-up needed for INT0 / INT1 | 01/01/70 00:00 | |
| Is the PIR output open collector? | 01/01/70 00:00 | |
| PIR is inverted using a BC547 | 01/01/70 00:00 | |
| Use a base-emitter resistor | 01/01/70 00:00 | |
| /INT0 : write 1 to config as i/p pin ? | 01/01/70 00:00 | |
| Of course you should be an input | 01/01/70 00:00 | |
Don't think that way! | 01/01/70 00:00 |