Lm231 Voltage to frequency converter help needed.

Discussion in 'General Electronics Chat' started by araforn, Jul 26, 2011.

  1. araforn

    Thread Starter New Member

    Jul 26, 2011
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    Hi guys.

    This is my first post on here and im really hoping somebody here can help. Im using labview to control a stepper motor and i want to create a variable speed pulse train in order to control the speed. I have the controller and the driver part sorted.

    I bought this lm231 ic, which is a voltage to frequency converter in the hope that i could use a 5v analog out signal from my usb daq device to control the output pulse train from the lm231.

    Alas i'm having problems with the wiring up of the application example which can be seen below. The VS here is 5v and the input voltage can go from 0 to 5v with the analog out from the daq. The components i'm using are not the exact values used in the example but i was hoping to get some kind of pulse out but so far the output from pin 3(Frequency Output) is just always high. I'm reading signals from pin 3 with a counter input on my usb daq but obviously since it is remaining high, there is no pulse or count. There is no counter output on the usb daq device. This is the reason I need to use this ic.


    Could anyone have a quick look at the below pics and see if im doing something obviously wrong??. As i said im new to electronics like this. :( . Any help would be greatly appreciated. Thanks in advance guys.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    The only immediately obvious thing I can see is that it looks like terminal 32 from the USB DAQ unit connects to IC pin 8. According to the User Guide (NI USB-6008/6009 User Guide and Specifications) terminal 32 of the DAQ unit is GND rather than +5V. Terminal 31 should be +5V I believe.

    There may be other errors but I haven't checked beyond that initial observation.

    Also noticed you don't seem to have cross board links between the upper and lower (+-) rail pairs on the proto-board. Normally these aren't linked internally within the proto-board. You have to usually make the links yourself.
     
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  3. SgtWookie

    Expert

    Jul 17, 2007
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    Hi araforn, and welcome to the Forums.

    You said:
    What are the exact differences in the components? This could be very relevant.

    If you can't tell us what values you've changed, then we don't know what your circuit is.

    Your breadboard is kind of messy and there is some stuff missing, and some really wrong values. You have the jumper from pins 1 to 6 OK, but things kind of go downhill from there. I don't see the 1uF mylar cap; instead I see a blue jumper going down to column 19 row J, and then a cap next to it (19I) and on that same column you have one end of a 100k resistor. I think you have the other cap lead connected over on column 23, along with the 100k resistor - then there's a blue jumper sneaking in from +V. If you've connected that to column 23 also, there's a problem; it's supposed to be 47 Ohms to ground. You also don't have the 22k resistor going to a trim pot.

    That 1uF cap labeled CL is supposed to be mylar, and you are trying to use an aluminum electrolytic. That's just not going to work. You might get away with a poly metal film instead.

    One really big problem is that you used the negative rail on the left side of the board, but you didn't connect it to ground. You seem to have connected the one on the right side to ground, but they don't connect on the underside of the board; the two power rails on the right are independent from each other, and also independent from the rails on the left.

    You seem to have a 4.7k resistor from pin 5 to 8 instead of the 6.8k resistor.
    Did you realize that you plugged the little cap in so that both its' pins are connected to pin 5, and you shorted pin 5 to +V with the blue jumper at j14? That's another big problem. You should replace that blue jumper with the 0.01uF cap.

    I don't know what you're trying to do with that 100 Ohm resistor from pin 3 to what you've already tried to use as ground. It needs to be 10k instead, and going to your +5 logic voltage. But, since you didn't connect the ground rail OR the +V rail on that side, everything will measure 5v, since that's what you're feeding to your +V rail on the right side.
     
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  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Found another error - at IC pin 5. You'll note the small orange cap (0.01uF?) is shorted by the connector array off pin 5 and then jumps to the rightmost supply rail - probably meant to be +5V. This means pin 5 is then shunted directly to that supply rail - rather than being in series with the cap to the rail (per the schematic). You need to jump the cap to an adjacent free connector array (say at line 15) then link from there to the supply rail.

    So there are plenty of things to fix and re-check. You obviously aren't too familiar with using this type of proto-board.
     
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  5. araforn

    Thread Starter New Member

    Jul 26, 2011
    18
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    Thanks for your replies guys. It's emabarrassing how bad I am with these :( . I actually have the left + and - connected. They're connected at the bottom of the board but you cant see in the pic. Sorry bout that.
    Your totally right about all the values. I only have a limited amount of resistors/capacitors and im going to order all of the correct ones tonight.
    Maybe I should have posted only then if I have trouble but I guess I'm too keen to troubleshoot the problem before I've did everything right first time. As soon as I have the correct value components I'll post and hopefully all will be fine. Thanks again.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Don't be embarrassed - I've done some pretty awful-looking things as well. I even managed to burn up a quad opamp a couple years back by plugging into the wrong power rails. :rolleyes: Stuff happens.

    If you don't have the exact values you need on hand, you can always use resistors in series and parallel to get a lot closer.

    Here's a very handy series/parallel calculator page:
    http://www.qsl.net/in3otd/parallr.html
    Bookmark it - you'll find it very useful.

    Here's a decade table of standard resistor values:
    http://www.logwell.com/tech/components/resistor_values.html
    Bookmark that, too.
    Values up to E12's are pretty commonly available, sometimes E24 as well.
    You'll generally have to order E48 and higher values; and they get quite a bit more expensive - not really a big deal if you just have a small project, but can be a chunk out of your wallet if you are stocking up.
     
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  7. araforn

    Thread Starter New Member

    Jul 26, 2011
    18
    0
    Hi guys.

    So I finally got some proper sized components and with some tinkering I've finally got the lm231 working perfectly. An analog output from the DAQ, with voltages varying from 0 to 3 volts gives me a perfect range of frequency in which to control the speed of my motor.

    Thanks again for your help. Here's the final circuit i used. It's used here with a step genie evaluation board to test a couple of unipolar motors I have. Now ive just got to build the entire board myself :eek: .
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Glad you got it working properly :)

    If you want a simple on-line tool to help you with laying out breadboards, veroboard and other kinds of stripboards, you might want to check out PEBBLE for PICAXE:
    http://www.rev-ed.co.uk/picaxe/pebble/

    I downloaded it to my computer; it's much faster that way.
    It'll help you keep your wires and things sorted out, as you can only lay them horizontally and vertically.
     
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