Author Topic: SBC68EC PWM frequency selection  (Read 2447 times)

hunterwu

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SBC68EC PWM frequency selection
« on: March 19, 2014, 09:06:34 PM »
Hello,everybody!
Currently , we are going to use your SBC68EC module to control one fan motor , but we found that you device only can set  3 PWM frequency.
Actually, we need 25kHz PWM frequency to control the fan , do you think it is possible to change the PWM frequency to 25kHz?

gr

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Re: SBC68EC PWM frequency selection
« Reply #1 on: March 20, 2014, 07:31:36 AM »
Wow - I haven't seen a post on here in a very long time.

I would be surprised if a fan cared if the power came on and off at 39Khz or 25Khz - it should be about the same.  In fact those both seem much too fast to control a fan - I would think you would want more like 10Hz.  I've seen fan controllers that turn the fan on and off around 10Hz - that's slow enough that you can do it in software instead of hardware.  You can probably get up to around 1khz with software.

Note that the power coming out of this board is unlikely to be enough to turn a fan - I believe most of the output pins are either 25ma or 50ma for this board (it's been a few years since I checked).  So you will need a darlington transistor or similar to increase the power to the fan(s).

Normally the PWM pins are meant to be filtered with an RC filter to get a constant voltage between 0 and 5v.

Have you looked into getting an arduino board instead?  You can get an arduino plus an ethernet shield for around half the price of this SBC board and it has similar capabilities.

modtro2

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Re: SBC68EC PWM frequency selection
« Reply #2 on: March 20, 2014, 03:15:15 PM »
Our new SBC66ECL and SBC66EC boards are much cheaper, and have much higher quality components than your average Arduino boards. They cost USD35 and USD42. Also much more compact, plenty of I/O, onboard 32MBit flash, EEPROM... The SBC66EC also has an industrial quality switch mode power supply with up to 40V input, where most Arduino board have simple linear power supplies. The MPLAB X IDE is also miles ahead of the Arduino IDE when it come to functionality!

modtro2

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Re: SBC68EC PWM frequency selection
« Reply #3 on: March 20, 2014, 03:35:23 PM »
Hi Hunter

Will you be modifying the software on the SBC68EC board, or using it with the supplied software? If you are going to be modifying the software, it is no problem setting the frequency to many other variations. See the PIC18F6680 chip for details on possible frequencies. I checked, and exactely 25kHz does not seem to be possible. Would 24kHz or 26kHz work too?

gr

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Re: SBC68EC PWM frequency selection
« Reply #4 on: March 20, 2014, 08:04:41 PM »
I stand corrected.  I guess I was thinking of the SBC65 and things must have progressed from there.

hunterwu

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Re: SBC68EC PWM frequency selection
« Reply #5 on: March 21, 2014, 08:19:14 PM »
Hello, everybody.
Thanks a lot for you reply!
I don't want to spend time to modify the software on the SBC68EC board.  i hope Modtronix can do this for us, we need to purchase a few for our fan testing project. we need to set the different PWM duty cycle to control the 54V DC fan(power from other resource) and reading back the actual fan speed via the tach signal. The purpose is to chech the fan is ok or not.  Fan spec define the PWM frequency is 25Khz, we think 24kHz or 26kHz should be ok. we will check with the fan vendor for the detail.