Need help determining PWM

Discussion in 'The Projects Forum' started by Rickmc3280, Mar 15, 2014.

  1. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    I have found the schematics for a board that controls a treadmill motor.

    I am trying to use an Arduino to send the signal instead of the upper controal board. In the schematics you can see from the Fast and Slow pins which are 5 and 6 that they send a signal to an 12F508 controller chip which outputs a pwm signal to an LED then to an Opto which then goes onto another microcontroller that sends the signal to the NPN and PNP transistors and 2 mosfets.

    Does anyone have an idea based on the schematics and commons sense what I could do to interpret the signal coming out of the second mincrocontroller that goes to the 2 Transistors and 2 Mosfets or a way to decode the signal coming from the first IC?

    Any help would be appreciated because I am trying to use this project to get into graduate school, (Human Factors Engineering). My focus is more on the Psychological side of Human Factors, but I have been picking up electronics as a hobby and all of these factors are well beyond me at this stage.

    Thank you,

    Rick
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Do you have a pdf of the schema ?
    Need a clear diagram, clear text, etc.
     
  3. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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  4. panic mode

    Senior Member

    Oct 10, 2011
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    geeez... i though you captured it on a shoe-phone but looking at that PDF tells different story, sorry for doubting you.

    CN12 pins 5 and 6 are just inputs coming from push buttons.
    PWM signal from controller goes through R25 to pair of BJTs acting as buffer stage driving mosfets. zener diode at gate is for protection of mosfet gates in case of spike/transient.
    mosfets are in parallel to share the load.

    PWM means Pulse Width Modulation
    http://en.wikipedia.org/wiki/Pulse-width_modulation
     
  5. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    Do you think that the PWM after the first IC is sending pwm data and the second and main controller is converting it to just regular old duty cycle?

    That is what I am trying to figure out; I would like to develop a touch screen program to control the speed via an Arduino and i need the arduino to send a signal that can control the board.

    I am familiar with using a soundcard oscilloscope, but have not been successful in seeing the PWM coming from the board, I outputted a pwm signal via the arduino and I could see it.
     
  6. #12

    Expert

    Nov 30, 2010
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    Pulse width modulation is so similar to duty cycle control that we need you to be real clear about your definitions. Please elaborate on what you think are the similarities and differences.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What is 'regular old duty cycle'?
    Max.
     
  8. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    Most of my confusion rests in 2 places

    Not knowing what the IC output is doing or can do, such as transmit data in bursts by duty cycle PWM (data) where the % = numbers that are then being calculated by the secondary microprocessor (the main one) which in the Schematic actually shows the processor putting out a PWM signal. - is that how it is being used? If not what could the 12F508 IC be outputting?

    2nd - What is going on with the BJT's which I am assuming from the previous poster ("Panic Mode") is the NPN and PNP's working together - to do what with the PWM signal?

    In the end, what I would like to figure out how to do is solely use the Arduino to output a PWM signal to control the motor, and I need to figure out where to inject the signal. The 12F508 chip is actually removeable and I can output a signal in the pin slot using a jumper wire. OR if I need to find the signal frequency, clock, and modulation info ONLY after the 2nd processors output, maybe while probing the resistor 25?

    I'm really lost in general. I had a lot of preconceived notions about how all this works, but when you start using IC's and other microcontroller/processors I'm lost and trying to figure out how to get back to understanding what it will take for me to be able to control this board.


    -Regular old duty cycle to me is what I had assumed is what people typically use PWM for - 0-5 voltage spikes over a length of time, not using the pulses to transmit data.
     
    Last edited: Mar 15, 2014
  9. panic mode

    Senior Member

    Oct 10, 2011
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    "BJTs acting as buffer stage driving mosfets"

    mosfets have high input impedance so static current is low (uA) but dynamic current is high because of capacitance of the gate. this is why BJTs are there - to handle large current required to charge and discharge gate capacitance.

    yes, if you remove PIC and bring wire from Arduino, you can drive the motor.

    you just need to generate PWM signal to vary duty cycle (control speed of the motor).
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The signal as labeled is PWM out to Q3 Q4 which are push-pull drivers to the Mosfets.
    If you bypass the control circuitry you could inject probably a 4Khz PWM signal into the 1k base resistor, not sure if this is what you are looking for?
    Max.
     
  11. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    Thank you Max and Panic,

    It is what I am trying to figure out how to do, but I am trying to find the safest way to send signals without "frying" the board.

    I was under the impression that I have to be extremely careful in what I do to the board because adding a load could change the operation of the motor etc.

    I guess really what I want to know is with yalls experience, if you wanted to control the speed, how would you do it?

    Edit to add:

    At this point I see 2 options, send a signal from the PIC or inject a signal after the circutiry directly to Q3 and Q4
     
    Last edited: Mar 15, 2014
  12. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    Also since the only input going to PIC12F508 is the push buttons from the main board, what is the PIC likely sending out? If I wanted to figure that out should I be looking for PWM signals or something else?
     
  13. panic mode

    Senior Member

    Oct 10, 2011
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    i see no PIC12C508.

    i would inject before BJTs, then you do not need to replicate that part of the circuit yourself or remove Q3/Q4 from original board (because they would short injected signal to GND).
    it is so much simpler to cut trace between R25 and pin6 of ALT-6000-1 and bring your signal to R25. and since the BJTs are configured as CC or voltage follower, amplitude of the PWM you inject into left side of R25 need to be 10-12V
     
  14. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    Well the board is identical to that of the schematics except for the PIC12_508 went from C to F where mine has PIC12F508

    How do you figure 10-12v? BC638 or PNP is -5 volts emitter voltage out and BC637 is +5 volts emitter out.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What are you trying to do exactly? Resurrect the existing T.M. board, or make a separate PWM motor controller that is not used on the T.M.?
    Max.
     
  16. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    TM board is working fine, what I would like to do is eventually get rid of the upper control board which is where the fast and slow inputs come from and tha has all the other push buttons, and just use the Arduino controlled by a program to send the signals to control speed.

    I want to use the board I already have, I dont want to make another one, unless its just a better choice.
     
  17. panic mode

    Senior Member

    Oct 10, 2011
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    ...sooo.... you want to control TM to prank people, make some "funny" videos..?
     
  18. panic mode

    Senior Member

    Oct 10, 2011
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    my secret weapon is called datasheet (and experience, plus that ZD2 rating speaks volumes):
     
  19. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    No lol. I want to use it to create a more interactive user experience that takes into account multiple factors to motivate users to follow through with their workout routine - specifically on cardiovascular equipment for 35+ minutes which can increase cognitive functioning, reduce symptoms of depression and anxiety, heal some human conditions, reverse diabetes, and other various physiological stuff like weight loss.

    I am still trying to get where you are coming from with the data sheet, that one you sent was not the PNP or NPN :-s
     
  20. Rickmc3280

    Thread Starter New Member

    Mar 9, 2014
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    I found this that explained to me what you were talking about - http://www.cn.njr.com/PDF/NJM2641_E.pdf - the very bottom explains what the ZD does - AKA Spike Killers - for any other newbies starting out like me.

    Thanks M8

    I have the datasheets for the transistors, but I still dont know what to make of them.

    Are there any resources yall recommend to help learn about what transistors do and the ratings because I still dont know how you arrived at 10-12v? I have an electronics for dummies book, i should probably open it back up...yeah.
     
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