Newbie..learning..help?

wayneh

Joined Sep 9, 2010
17,496
RS used to sell a bag of multiple resistor values, maybe 200 to 500 in all. It's lasted me a long time. I'm not sure they still offer it though. If not, I'd stick with what you have. Does Mouser have similar minimum quantities? I wouldn't balk at 20, but you'll never use up 100.
 

KMoffett

Joined Dec 19, 2007
2,918
After looking at the site, I noticed that Brad Collins, that designed the circuit, is PWM'ing BLDC fans at 20KHz. Does anyone have any experience with the efficacy of doing that?

Ken
 

KMoffett

Joined Dec 19, 2007
2,918
Normally, pulse-width modulation (PWM) is used to control the speed of brushed-type DC motors. Brushless-DC (BLDC) motors, like the ones Brad posted on his site, have complex internal electronics that control the rotation and speed. Trying to control the speed of BLDC fans by driving them with PWM voltages seems to be counterproductive.

Ken
 

Thread Starter

james211

Joined May 29, 2012
283
I have a question about the temp sensor I purchased, the DS18B20 1 Wire temp sensor. It says the brown wire is for both power and ground, and the blue is for the data in and out. I'm putting everything together on a breadboard first to test everything, and I'm not sure how I would go about doing power and ground to one wire, any help? I've attached the schematic as well as the sensor data sheet.
 

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wayneh

Joined Sep 9, 2010
17,496
As the datasheet clearly shows, power and ground get their own wires. All data passes (digitally, serially) over one wire, as opposed to a parallel arrangement.

You might prefer the LM35 if you're not prepared to handle the data communication.
 

Thread Starter

james211

Joined May 29, 2012
283
ok, I think I got it. The fan is on, but its not responding to the sensor, its just on. So I either have the MOSFET wired wrong, or the sensor is not being read properly. Any idea's how to check this?

By the way, here is how the MOSFET is wired in.
Pin#1: Connected to P2 on IC
Pin#2: Goes to Fan Ground
Pin#3: Ground

In the schematic it looks like there is a small jumper going between pins 1 & 3 but I could just be reading it wrong.

I appreciate your patience with my ignorance.
 

wayneh

Joined Sep 9, 2010
17,496
Ah yes, sorry, missed that. The Vdd pin is grounded (brown wire to ground) and this allows the device to power itself from incoming data. So, 3-pin device becomes 2-pin cable, brown is grounded, blue is data and parasitic power.
 

Thread Starter

james211

Joined May 29, 2012
283
Yeah I got that figured out after some reading. Now I think its the Mosfet that I may not have wired correctly. Any ideas?
 

KMoffett

Joined Dec 19, 2007
2,918
For the MOSFET pinout:http://audiolabga.com/pdf/BUZ71A.pdf
The datasheet shows the gate 'threshold' as 2.1-4V. This is not a good choice for a 5V output from the PICAXE. You would be better off with a "logic level" MOSFET.
But, to check that the output of the PICAXE is working OK at 5V with the sensor, remove the MOSFET and put an LED and a 330ohm resistor from ground to P2, like you did for P1.

You can also use "debug" in the program to monitor the data coming from the sensor.

Ken
 

Thread Starter

james211

Joined May 29, 2012
283
This is the Mosfet I purchased, http://bit.ly/LoCs1h, not sure what that changes. I did what you said and plugged an LED into P2 with a 330ohm resistor and didn't get any response. I'll debug it tomorrow and see what I can figure out.

I appreciate your help.
 

KMoffett

Joined Dec 19, 2007
2,918
The IRLZ24NPBF has a Vgs threshold between 1V and 2V, so should work OK with the PICAXE's output.

I don't think the circuit and program are "drop-in" compatible with the 2-lead version of the sensor. If you want to stick with the original design and program, you should get the correct sensor.

Ken
 

Thread Starter

james211

Joined May 29, 2012
283
Understandable. If I pull apart the version I have, will it have three prongs or two? I was just wondering if I could take it apart just to test it.
 

Thread Starter

james211

Joined May 29, 2012
283
On a side note, I have a small device that is powered by 2-AA batteries and I want to hook it up to a power supply. Can I just purchase a 3-3.5 volt power supply or would it be better to build one that would suite it better?

Either way, if I buy a power supply, any details I need to know? If I build one, do you know where I can get a schematic?
 

MrChips

Joined Oct 2, 2009
30,714
The devil is in the details. What is your "small device"?
How much volts and current does it require?
Power supplies at 3V are uncommon. Look for the lowest voltage (around 5VDC) wall adapter you can buy and get a 3V or 3.3V voltage regulator.
 

Thread Starter

james211

Joined May 29, 2012
283
I have a 5 volt DC wall adapter at home. What I wasn't sure was if it was better to use a few rectifier diodes in series or a voltage regulator. What would be the difference?
 

MrChips

Joined Oct 2, 2009
30,714
Again, it depends on what you are powering and how sensitive it is to supply voltage.
Add three diodes in series and see what happens. What is the current drain?
 
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