I have a problem and could use some advice…We all remember I am an electronics idiot. I asked Macro if I could use his PWM circuit for Gothic and he said it was for the world to use…so I got the parts and put it on my proto-board. The thing works but I can not get the fan to change RPMs. I replaced the thermistor with a 10K vari (red arrow) and the blue arrow is also a 10K vari. Everything is per Macro’s specs…What the **** did I do wrong? How would I troubleshoot this?
Apart from the obvious check the circuit, one reason for the circuit not working could well be the breadboard you are using. During the development I found the chip to be influenced by board layout probably due to stray capacitance. The type board you are using is notorious for having considerable capacitance. You can try bunching the components closer together but I would recommend building it on a small piece of stripboard to test it.
I found just touching multimeter probes to the fan leads made the full-speed do-dah initiate. Very sensitive. Lot cheaper
I will remove this from the proto-board and build it on a board. I have some of those cheap radio shack boards. Cpemma where did that schem come from? Unfortunately, I have all the part to build 5 of Macro’s circuits…but if I can’t (in my limited capacity) get this working I may need it. Does it use a thermistor?...back to the lab… Thanks guys…again!
It's a 0-100% range pot driven variation of this thermal one. I guarantee the thermal version works. Above needs a few smoothing/decoupling caps, same as thermal version.
Hey cpemma, been round you're site and looking at you're different circuits... nad was wondering if you could make something simular to this: http://forums.bit-tech.net/showthread.php?t=34194 I'm not that good at electronics (or english for that matter ), so if you could come up with something like that.... it would be great
Push-button fan control isn't hard, the complex bit is getting a circuit that remembers the last setting after you've rebooted. That probably involves RAM and a nasty PIC beasty. VSB
Don't be silly cpemma there is no need to resort to a MCU when it would only make the whole thing in ONE chip, and a hell of a lot easyer. Parrallel EEPROM is the awnser. Using standard up/^down counters, save the value into the EEPROM after each change, And query the EEPROM, for each speed setting ! simps!
Bluebark, what resistors are you using? I'm planning to make the circuit but the Rapid codes for the resistors have expired or something and so I don't know what tolerance or power rating I need
You jammy git... Cheers for the res info though I think there were some people looking for MICs here [edit] Hell, I'd take two or three myself depending on how much postage to Northern Ireland was [/edit]
Revise that - have you any MIC52BNs still handy? Rapid have discontinued them without updating their online catalogue... *******s... so anyway I need a few of the chips myself
There's no need for anything over 0.25W, except maybe for the one to the transistor base, 0.5W better there. 10% are fine. But Maplin's 0.6W 1% metal film do for nearly everything you're likely to build, same spec as the Rapid codes in the article.
When I looked up Macro's PN#'s they were both 2W so that’s what I got. I build the circuit on a small board and it does nothing... Tomorrow I will trace the lines and post a pic of what I built and you guys can tell me what an idiot I am...'cause I just don't see anything wrong...save the fan not turning...
Not in my paper catalogue. All are TruOhm MF60 0.6W 1% metal film resistors. Page 474 on the pdf file. R1 10k 62-2146 R2 15k 62-2154 R4 270R 62-2070
I finally got Macro’s fan circuit up and running…and I took you’re advice Cpemma and went with smaller wattage resistors. I had to replace the 10K var. resistor with a 20K one because the 10K res. did not bring the fan speed low enough for me. As you can see, I have the thermistor removed and jumped to represent a thermistor at full throttle. But I’m only getting 6.7V (about) out of the circuit. If I replace R1 (15K) with something smaller will that boost the voltage to the fan? Also, I intend on putting the var. resistor on another board. Will this have an impact on the circuit?
With a 20k pot and 15k resistor the pin #1 input will range from (100*15/35) = 42.8% up to 100% of supply. From the datasheet, 30% = zero PWM duty cycle, 70% = 100% duty cycle, so you should be getting around 6v minimum and a shade over 11v max. when the pot's half-wound. I used resistors as below for a pot version, gives about 42.8%-71.4% voltage input, so your's is similar and should give the most useful speed range (IMNSHO). If it don't work, you've messed up somewhere.
