| Electronics > Beginners |
| Please help me understand this circuit |
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| Moriambar:
Thanks to all. I understand what you say about the LED differences. I will try Zero999's circuit tomorrow and then try to tweak values etc. Sorry for the monster image file. |
| Moriambar:
--- Quote from: Richard Crowley on January 26, 2019, 05:40:06 pm --- Changing the current through an LED is not a popular way of controlling light output. Again, because of slight differences between LEDs, it is difficult to get consistent results. That is why PWM is commonly used for controlling LED brightness. --- End quote --- Pardon my noobeness, but if the slight differences are what prevent us to get consistent results, then how does PWM give consistency? |
| Richard Crowley:
--- Quote from: Moriambar on January 26, 2019, 06:37:10 pm ---if the slight differences are what prevent us to get consistent results, then how does PWM give consistency? --- End quote --- The LEDs are driven to a consistent point in their operating range, and then "chopped" in time which is very consistent and repeatable. If you had a reliable way of measuring brightness, you could experiment by drawing voltage/current vs. brightness curves for various LED examples. |
| MarkF:
If you use a SPDT switch, you can control both the turn on time (via R1) and the turn off time (via R2). Maybe start with R1=10K, R2=1K and C1=100nF. OR Just add a resistor in parallel with the capacitor in your original circuit. You would need to keep in mind the series current when the switch is on if you do this. |
| Doctorandus_P:
I've added an PNP transistor and a resistor to drain the 1mF capacitor when the switch opens. I've also attached the project in KiCad format. So instead of everybody re-drawing the whole thing you can take this project, modify it a bit and post a screenshot :) KiCad is fully Free and Open Source Software. No hidden agenda's, no misty stealing of your intellectual property, no artificial limits on for example board size or number of pins. No limited time edition. And it is being improved significantly every year. Do not believe a 2 year old review :) |
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