| ??? 02/07/10 14:10 Read: times Msg Score: +1 +1 Informative |
#172956 - Never discharge a cap directly by a switch! Responding to: ???'s previous message |
Joel said:
@ everyone else - thankyou very much, I have tried another implementation of the switches on a separate piece of veroboard and changed the (what i thought to be brand new but cheap) switches for the ones I had ordered to be used on the final version. These work far more reliably! The mistake is, that your switch directly discharges a cap without any current limiting! That burns down the contacts and results in a little, non-conducting oxid spot. Always limit the current rushing through such a tiny switch to less than a few mA. So, don't discharge the cap directly, but via a resistor. Just put a resistor in series to the contacts, like shown in this example: 
I think the evalboard from SILABS has 100k pullups? Then a current limiting resistor of 2k2 is adequate. The current through such a switch should be more than 100µA, but less than 5mA, for reliable switching. Kai Klaas |
| Topic | Author | Date |
| Buttons - Hardware | 01/01/70 00:00 | |
| do double check .... | 01/01/70 00:00 | |
| Debouncing | 01/01/70 00:00 | |
| Have you considered that it could simply be the "breadboard" | 01/01/70 00:00 | |
| I (dis)agree | 01/01/70 00:00 | |
| Relevance to pushbuttons | 01/01/70 00:00 | |
| Consider the objective | 01/01/70 00:00 | |
| Agreed | 01/01/70 00:00 | |
| that's why there's so fluid a definition for "working" | 01/01/70 00:00 | |
| PCB's to match the contact arrangement on a "breadboard" | 01/01/70 00:00 | |
| Not exactly ... | 01/01/70 00:00 | |
| Solved: | 01/01/70 00:00 | |
Never discharge a cap directly by a switch! | 01/01/70 00:00 |