| Electronics > Beginners |
| Trying to build a PWM fan controller |
| << < (5/5) |
| eamoex:
Thanks Ian.M and rstofer. I'm using Ian.M's schematics so I only need 12V (handy!). --- Quote from: rstofer on January 23, 2019, 09:03:06 pm ---Without the pull-up resistor, all you're going to see is trash. --- End quote --- Yeah... struggling a bit to grasp the ideas behind open drain/collector and pull-up/down. I get it when I read about it but then forget what it's about 3 minutes later. I need more practice. By the way, trash very accurately describes what I see. ;D Will try out the 10K pull-up and report. |
| eamoex:
--- Quote from: rstofer on January 23, 2019, 09:03:06 pm ---Whatever mechanism they use internally, perhaps photoelectric or maybe hall effect, will have an on time proportional to speed. --- End quote --- When you say "an on time proportional to speed", you mean a linear variation in frequency, not duty cycle, right? |
| aheid:
--- Quote from: eamoex on January 23, 2019, 09:50:51 pm --- --- Quote from: rstofer on January 23, 2019, 09:03:06 pm ---Whatever mechanism they use internally, perhaps photoelectric or maybe hall effect, will have an on time proportional to speed. --- End quote --- When you say "an on time proportional to speed", you mean a linear variation in frequency, not duty cycle, right? --- End quote --- Yes. Emphasis mine: --- Quote from: 4-Wire Pulse Width Modulation (PWM) Controlled Fans Specification v1.2 ---2.3 Tachometer Output Signal Fan shall provide tachometer output signal with the following characteristics: • Two pulses per revolution • Open-collector or open-drain type output • Motherboard will have a pull up to 12V, maximum 13.2V --- End quote --- Note that you're playing the role of the motherboard in this setting, the spec is written from the POV of the fan. You'll pull the line up, and the fan will pulse it low two times per revolution. |
| eamoex:
Inserted a 10K pull-up resistor and the tach signal is PERFECT, even cleaner than the 555 one, no overshoot. Fan speed range is almost perfectly in spec, ranging from a perfect 500 to 1950-ish revolutions per minute. Now this thread is out here for anyone trying to do the same thing! You guys rock, thank you. 8) :-+ EDIT: when I bought this second hand scope, little did I know about the level of satisfaction that can be brought by watching a green line moving on a 3 inch CRT. |
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