| ??? 03/01/11 07:03 Read: times |
#181362 - caps in datasheet for 7805 Responding to: ???'s previous message |
F Y Didik Chandra said:
"...the obligatory 100nF caps at each chip right across the supply pins and at the input and output of 7805. "
I don't understand this one ... Look at the datasheet for the 7805 - it is always shown with capacitor on input and capacitor on output. Obligatory, because it is designed to have them even. "The RC-reset at µC is highly disadvantageous. Use a proper reset chip to provide a true power-on reset and brown-out detection. I like to use the MAX1232 and its built-in watchdog, like shown in this example here: "
I'm all up to better ideas. What is the advantage of using your circuit? I've been using this RC method in many of my circuits before ... Fortunately they are working fine up until now. Most probably not. But they may seem to be working fine if you don't have short power glitches, in which case the voltage may drop enough that the processor fails running the program but without the RC reset circuit managing to issue a new reset. The RC reset circuit just works when your power gets activated without any glitches and power failures are long enough to take care of any charge in the capacitor. Alas, lots of people only test with optimum power conditions and then doesn't notices any problems. So when they do get problems, they "know" where to not work since they "know" their RC resets are working fine. One question after seeing your PCB ... What are pin "3" and "4" of the crystal used for ( My crystal only has 2 pins ) ? And what are they connected to ( Ground )?
Many crystals have extra wires for grounding the can of the crystal. And for crystals who doesn't have these ground wires, many designs have a wire drawn above the crystal to "tie it down" to the PCB. |
| Topic | Author | Date |
| Verifying Circuit and Program | 01/01/70 00:00 | |
| Attachement? | 01/01/70 00:00 | |
| Verifying Circuit and Program - Attachment ? | 01/01/70 00:00 | |
| You think we can all access your hard drive? | 01/01/70 00:00 | |
| You think we can all access your hard drive? | 01/01/70 00:00 | |
| As a member.... | 01/01/70 00:00 | |
| As a member.... | 01/01/70 00:00 | |
| I miss... | 01/01/70 00:00 | |
| I miss... | 01/01/70 00:00 | |
| Next try out | 01/01/70 00:00 | |
| caps in datasheet for 7805 | 01/01/70 00:00 | |
| caps in datasheet for 7805 | 01/01/70 00:00 | |
| Soldering the can... | 01/01/70 00:00 | |
| Price of MAX1232 to AT89S51 | 01/01/70 00:00 | |
| alternatives exists | 01/01/70 00:00 | |
| Great thanks | 01/01/70 00:00 | |
| Links... | 01/01/70 00:00 | |
| Update | 01/01/70 00:00 | |
| Some points... | 01/01/70 00:00 | |
Some Points Updated | 01/01/70 00:00 |