Hi everybody, It's both a honor and a pleasure for me to post in here, the forum from which the world's most famous casemods came. I've posted this question in some forums I used to participate, joined some in my country (Brazil), and nobody could help me much. I don't know much of electronics, but since I asked for help in the forums to now, I **almost** managed to create part of the circuit myself. Almost because, as I said, I'm not an expert in electronics, but I did find an integrated circuit which does about what I need. What I want is to measure the RPMs of a fan (actually, 8 fans, but I guess a simple switch would do the trick) in one 'multmeter' and the temperature of 4 spots in another multmeter (again, a switch would be needed). The thing is: I don't know how I would do the thermometer thing, and I found an IC (LM2907) that would convert frequency to voltage, but I got all messed up in the formulas from it's datasheet. So is there anyone who managed to do a digital thermometer (by digital i mean using thermistors or any kind of sensors, with an output as 'voltage' for a multmeter), or a tachometer (also, outputting to a multmeter)? Thank you all for your atention, and for the inspiration this forum brings me! Best wishes, Guilherme H.
LM2907, you'll have to persevere with the datasheet, you'll need an adjustable pot to calibrate the output to match the fan RPM. Vout = 12 x fin x C1 x R1 for a 12V supply, so pick a suitable C1 and tweak R1. Points to remember, the fan speed wire is often open-collector switching, so you'll need a pull-up resistor to 12V to get a nice square-wave input. the speed wire switches twice per rev, so a 2000rpm fan speed will give 4000 pulse/minute, 66.7Hz. On temperature, forget thermistors, the temperature/resistance curve is very non-linear so you really need a PIC or similar to make sense of it. Instead, LM35 or LM135 temperature sensors produce a linear output.
hello brazilian friend como está isso ai no Rio de Janeiro? bem vindo ao melhor forum de modding da net "how is it there in Rio de Janeiro? welcome to the best modding forum on the net "
Hello cpemma! That formula seems to be ok, this is what I got: Vout = 10V Vcc = 12V Fin = 166,7 (5.000 RPM, two pulses per revolution. Though it's said that some fans send 1 pulse) 10 = 166,7 × 12 × C1 × R1 C1 × R1 = 200,04 Now if you take a look at page 3 of it's datasheet, you'll see a lot of formulas. Also, there is a formula for 'Choosing R1 and C1' at page 7. And then I'm screwed. And... Er... I didn't get the pull up resistor part... What is an 'open collector switching'...? Heheh Oh, by the way! I'm gonna use one of your low-dropout circuits. Does the voltage in Fin affect the results? DXR_13KE Hey fellow! It's been sunny and rainy down here. Fortunately, more sunny than rainy in the last week. And how is it up there in Madeira? Hehehe I'm sure this is the best modding forum all over! Always wonder why I didn't post in here before... By the way, Sunny was the name of my dog. I find the word itself shines just like she did... =)
Man, I'm going crazy... LOL Let's see if I get it: I need to use a PNP transistor between the 0V and the tacho signal, right? What kind of transistor, I mean, any model in specific? And do you have any idea on what R1 and C1 I would need...? Thanks again, man! Best wishes
