Hi everybody, I'm new here
I have a question regarding a PWM circuit using 74AC14 chip. I want to construct a simple thingy with three independently variable LEDs (conveniently red, green & blue) and the circuit I found at robotroom.com would allow me to fully use the 6 Schmitt Triggers of said IC.
I made this circuit on a breadboard and it appears to work. But I don't have an oscilloscope to visualise the output. But the circuit (and robotroom's explanation) leave me confused.
If you look at the explanation at this page, you see what's happening, the one Schmitt's input is low, so output is high, charge flows through R2 and D1 into C2. So far so good.
But then, when the capacitor is charged enough, he explains it will discharge and there'll be a current going through D2, back into R2 and then into the Schmitt's output pin. This part I don't get. Why would charge flow through a resistor into an output pin, when there's a perfectly resistance-free path waiting for it, directly connected to 74AC14's input pin? Wouldn't the cap discharge directly and always fast, without resistor, into pin 1? I can't find any info in the chip's datasheet about output being a current sink when low.
But that's not all. If you read on, on page 4 of the explanation, you'll see he directly hooks up output 1 (pin 2) to input 2 (pin 3), so that anything connected to the output, the device to be modulated (like an LED or a transistor) will not interfere with the whole RC contraption. Well that's all fine.
But if we follow the explanation of the earlier page, as to how this circuit works, with the cap discharging in output 1, wouldn't that mean the capacitor is really discharging into input 2 instead?
So you see this has me confused. I can see how this would work, but it would be the same if we'd leave D2 out and that wouldn't result in an optimal PWM, I think. I'm probably overlooking something, so any help is welcome.
Thanks in advance!
I have a question regarding a PWM circuit using 74AC14 chip. I want to construct a simple thingy with three independently variable LEDs (conveniently red, green & blue) and the circuit I found at robotroom.com would allow me to fully use the 6 Schmitt Triggers of said IC.
I made this circuit on a breadboard and it appears to work. But I don't have an oscilloscope to visualise the output. But the circuit (and robotroom's explanation) leave me confused.
If you look at the explanation at this page, you see what's happening, the one Schmitt's input is low, so output is high, charge flows through R2 and D1 into C2. So far so good.
But then, when the capacitor is charged enough, he explains it will discharge and there'll be a current going through D2, back into R2 and then into the Schmitt's output pin. This part I don't get. Why would charge flow through a resistor into an output pin, when there's a perfectly resistance-free path waiting for it, directly connected to 74AC14's input pin? Wouldn't the cap discharge directly and always fast, without resistor, into pin 1? I can't find any info in the chip's datasheet about output being a current sink when low.
But that's not all. If you read on, on page 4 of the explanation, you'll see he directly hooks up output 1 (pin 2) to input 2 (pin 3), so that anything connected to the output, the device to be modulated (like an LED or a transistor) will not interfere with the whole RC contraption. Well that's all fine.
But if we follow the explanation of the earlier page, as to how this circuit works, with the cap discharging in output 1, wouldn't that mean the capacitor is really discharging into input 2 instead?
So you see this has me confused. I can see how this would work, but it would be the same if we'd leave D2 out and that wouldn't result in an optimal PWM, I think. I'm probably overlooking something, so any help is welcome.
Thanks in advance!