| ??? 11/13/09 17:24 Read: times |
#170761 - Very good Responding to: ???'s previous message |
Siddharth Das said:
INT0 on AT89S52, interrupt is source is LM324 wired as a comparator,that is used to sense IR radiation. The reference voltage is set such that the comparator outputs a high to low pulse to the interrupt.The interrupt is setup as falling edge triggered and the ISR toggles the LED state each time an interrupt is received. The problem is when there is no such change in IR levels,the LED blinks nevertheless,which can only mean the ISR is being executed by false trigerring. Now THAT is helpful. Like Andy said, I'd watch this with an oscilloscope. I'd also tie the pin into a high state, and see if it STILL triggers. Have you got adequate hysteresis on the comparator - they are REALLY noisy if you haven't ? Steve |
| Topic | Author | Date |
| interrupt trouble | 01/01/70 00:00 | |
| Much more info needed | 01/01/70 00:00 | |
| more info | 01/01/70 00:00 | |
| Have you looked at all signals? | 01/01/70 00:00 | |
| yet more info | 01/01/70 00:00 | |
| Some hints | 01/01/70 00:00 | |
| No | 01/01/70 00:00 | |
| Doesn't the '324 have an OC output? | 01/01/70 00:00 | |
| Very good | 01/01/70 00:00 | |
| Debugging time! | 01/01/70 00:00 | |
| no oscilloscope :( | 01/01/70 00:00 | |
| then try 'selective grounding' | 01/01/70 00:00 | |
| This might be the reason | 01/01/70 00:00 | |
| Dangerous approach! | 01/01/70 00:00 | |
| Correct | 01/01/70 00:00 | |
| hysteresis? | 01/01/70 00:00 | |
| aka positive feedback | 01/01/70 00:00 | |
Dead gap | 01/01/70 00:00 |