Timeline for Simple LED indicator for audio signals
Current License: CC BY-SA 4.0
4 events
| when toggle format | what | by | license | comment | |
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| Oct 12, 2023 at 10:03 | comment | added | danmcb | you will current limit the output stage of the 339 with this, because of the high discharge current of the cap, which needs to be fairly large to keep the LED on for any reasonable length of time. The chip will likely be OK but it could cause other problems like low level clicks in other sensitive parts of the circuit. A low value series resistor in series with the cap would be wise. | |
| Apr 19, 2023 at 19:20 | comment | added | td127 | To clarify - "The upper end of the common-mode voltage range is limited by VCC – 2V. However only one input needs to be in the valid common mode range, the other input can go up the maximum VCC level and the comparator provides a proper output state. Either or both inputs can go to maximum VCC level without damage." So keep reference (+ input) below VCC-2. But the audio_in does need to be biased (above 0). This is straightforward in a single-supply system but for bipolar supplies and signals the LM339 is not a great choice. | |
| Apr 19, 2023 at 19:02 | comment | added | Justme | It only works if audio is between 0V and about 2V below VCC supply. But audio generally is biased to 0V and goes below 0V and above 0V. A typical modern line out would be 2Vrms or 5.6Vpp, going 2.8V negative and 2.8V positive. So this circuit alone won't be very good. | |
| Apr 19, 2023 at 18:53 | history | answered | td127 | CC BY-SA 4.0 |