darkenreaper57
- Jul 25, 2005
- 6
- Joined
- Jul 25, 2005
- Messages
- 6
First off, I'm new here and I'm not entirely sure my post is in the correct forum.
But anyway...
I am a EE student at UCF. I haven't begun my major courses just yet, so I have little background in electronics. Everything I know thus far has only been covered in AP physics B and what I have read on my own. Suffice to say, I am a newbie - but I am learning
.
Anyway, I am building this PWM fan controlling circuit for a project by following a guide (link below). It is based off of the 555 timer IC and the uA741 op-amp. I am also integrating the voltage monitoring circuit as described later on.
I already have most of the parts, and can pick up the remaining ones at radioshack. Here is the link to the guide: http://casemods.pointofnoreturn.org/pwm/circuit3.html
Now, the author recommends that if I integrate this voltage monitoring circuit http://casemods.pointofnoreturn.org/voltmon/tutorial-full.html that I "might want to change the VLo and VHi signals on the LM3914 chip to 4V and 8V." The monitoring circuit sensor signal is connected to pin 2 on the op-amp.
Hhow exactly would I change these signals, and exactly what are they? In the VRM guide, the closest things I see to "VLo" and "VHi" are RLO and RHI, respectively. Are these the same thing?
At the end of the VRM guide, he tells the reader how to chance RHI. Here is a quote:
"One last note - what if I want to use a different high value than 12V - say, 7V or 5V? In this case, get a second resistor and place it next to R1 - connect R1 to it in series, and connect this new one (call it R4) to ground. Disconnect pin 8 from ground and connect it to the middle between R1 and R4. Then, the top LED will be equal to 1.25 * (1 + R4 / R1) - it's identical to a LM317."
If my math is right, this means that R4=6.48k. The closest resistors are 6.2 and 6.7k (but I can run some in parallel or series to get closer to the target 6.48).
Is this all I would need to do? Wouldn't I need to do something different to change RLO? It is very possible that my math (or logic) is wrong, as I am a newbie to electronics.
One more thing - on this circuit http://casemods.pointofnoreturn.org/pwm/circuit3.html a .01 uF capacitor connect pin 5 of the 555 timer chip to ground. Would it be ok to substitute a different cap there? Unfortunately I forgot to order .01 uF caps (but have .1 uF caps).
Thanks a ton for any assistance!
But anyway...
I am a EE student at UCF. I haven't begun my major courses just yet, so I have little background in electronics. Everything I know thus far has only been covered in AP physics B and what I have read on my own. Suffice to say, I am a newbie - but I am learning
.Anyway, I am building this PWM fan controlling circuit for a project by following a guide (link below). It is based off of the 555 timer IC and the uA741 op-amp. I am also integrating the voltage monitoring circuit as described later on.
I already have most of the parts, and can pick up the remaining ones at radioshack. Here is the link to the guide: http://casemods.pointofnoreturn.org/pwm/circuit3.html
Now, the author recommends that if I integrate this voltage monitoring circuit http://casemods.pointofnoreturn.org/voltmon/tutorial-full.html that I "might want to change the VLo and VHi signals on the LM3914 chip to 4V and 8V." The monitoring circuit sensor signal is connected to pin 2 on the op-amp.
Hhow exactly would I change these signals, and exactly what are they? In the VRM guide, the closest things I see to "VLo" and "VHi" are RLO and RHI, respectively. Are these the same thing?
At the end of the VRM guide, he tells the reader how to chance RHI. Here is a quote:
"One last note - what if I want to use a different high value than 12V - say, 7V or 5V? In this case, get a second resistor and place it next to R1 - connect R1 to it in series, and connect this new one (call it R4) to ground. Disconnect pin 8 from ground and connect it to the middle between R1 and R4. Then, the top LED will be equal to 1.25 * (1 + R4 / R1) - it's identical to a LM317."
If my math is right, this means that R4=6.48k. The closest resistors are 6.2 and 6.7k (but I can run some in parallel or series to get closer to the target 6.48).
Is this all I would need to do? Wouldn't I need to do something different to change RLO? It is very possible that my math (or logic) is wrong, as I am a newbie to electronics.
One more thing - on this circuit http://casemods.pointofnoreturn.org/pwm/circuit3.html a .01 uF capacitor connect pin 5 of the 555 timer chip to ground. Would it be ok to substitute a different cap there? Unfortunately I forgot to order .01 uF caps (but have .1 uF caps).
Thanks a ton for any assistance!
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