Help developing digital distance counter.

Discussion in 'The Projects Forum' started by GMPRuss, Mar 15, 2013.

  1. GMPRuss

    Thread Starter New Member

    Mar 11, 2013
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    We are currently using a rotary encoder that provides 200 pulses per revolution to a programmable 6-digit LED display (Crouzet CTR24L) to measure the distance and speed for a cable installation device. While this combination works very well with our prototype, we need to reduce the size of the display. The Crouzet CTR24L is is the smallest display I can find on the market. We only need a 4-digit LED or backlit LCD display. I thought if I can separate the display from the logic portion of the display I could place them in the enclosure in such a way to reduce the overall size of the enclosure. Can someone help me with identifying a 4-digit LED or backlit LCD display along with a logic board that we can program to give us distance and rate in Ft. & Ft./Min. or Meters & Meters/Min. with the signal we are getting from the rotary encoder similar to the Crouzet display?
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    How small do you need it?
    Is this a one-off?
    Do you have any programming experience?
     
  3. GMPRuss

    Thread Starter New Member

    Mar 11, 2013
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    I currently have the enclosure at 3" x 3" x 2-1/2" and that is too big. I am not sure the finished size of the enclosure it just has to be as small as possible.

    This is not a one-off we plan to go into production with this product in quantities of 50 to 100 per year.

    I have no programming experience.
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    A 8 char 2 line LCD is very small, and give you nice text posibilities on two lines. There are tons of them on ebay.
     
  5. GMPRuss

    Thread Starter New Member

    Mar 11, 2013
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    An 8 character 2 line LCD is more than we need. We only need 4 characters which will give us a maximum reading of 9,999 Ft. or Meters.
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    You said
    "we can program to give us distance and rate in Ft. & Ft./Min. or Meters & Meters/Min."

    A 8*2 char display lets you show more stuff, like both imperial metric, or averages, or setpoints etc all with text description, and adds value to your product.

    Also you can drive it direct from your microcontroller with only 6 pins.

    A 4 digit 7seg display requires 28 or 32 pins, or requires 12 pins, 8 resistors and 4 FETs to drive it, and has a lower perceived tech level and lower perceived product value.

    Anyway, it's your call. :)
     
    Last edited: Mar 20, 2013
  7. elec_mech

    Senior Member

    Nov 12, 2008
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    If the goal is to get it as small as possible, I don't think you can get your digits any smaller - according to the datasheet on your product, the counter itself is 24mm x 48mm or 0.94" x 1.88". Looking for smallest display available on Digikey.com and Mouser.com, I found ~10mm x 32mm in 7-segment or ~10mm x 18mm in 5x7 dot matrix. Based solely on the drawing in the datasheet, these seem pretty close in size to what is on your unit.

    Now, if you're simply trying to separate the display from the logic portion and house each in a separate enclosure some distance apart, you can simply take apart your unit and do so. The display is likely on its own board and connected to the logic board through wires. You can replace the wires with longer ones and separate the two.

    Is this what you're trying to do or are you trying to replace the Crouzet unit as a whole with something smaller altogether? If yes to the latter, then again note the digits will not change size as you likely can't readily get anything smaller, though you could move the buttons to the side of the display and probably make the unit as a whole thinner but a little wider. As others have alluded however, this would require programming your own microcontroller as well as designing a circuit, designing a PCB, having the PCBs made, and soldering the parts to the board. Not knowing more about your goals, I'd suggest taking the Crouzet unit apart and bending it to your will, so to speak. :)
     
  8. GMPRuss

    Thread Starter New Member

    Mar 11, 2013
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    Great suggestion regarding the 8 character, 2 line LCD. The product we are developing is very low tech and our customer only requires distance and speed be displayed. I did find a 4-digit LED, Lascar EM32-4-LED, that might work very well. It has the resistors and FET's built in. The only thing I am missing is what goes between the encoder signal and the display. You seemed to have answered that question when you said we can drive the display with our microcontroller. I think I am missing a microcontroller. Can you point me in the direction of what kind of microcontroller I would need to take the signal from the encoder and drive the display to alternately show distance and speed perhaps by depressing a normally closed momentary button? Keep in mind I am a ME trying to learn a small part of what EE's do. We want to program the microcontroller to increment the display 1 digit for every 509 pulses from the encoder when we want it to show Feet or every 1,671 pulses when we want it to show distance in meters. We do not need the the display to alternately show Feet and Meters. Once programmed for either feet or meters the unit will stay that way unless there is an easy way to change the scale factor in the field. I assume the microcontroller will need a clock if we are to show the speed at which the cable is passing through the device. We would like to power the encoder, the microcontroller and the display using a typical 9V battery. Is this possible?
     
  9. GMPRuss

    Thread Starter New Member

    Mar 11, 2013
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    We did consider taking the Crouzet apart and doing exactly what you suggested. I even contacted Crouzet to see if we would provide us the display detached from the microcontroller, they declined to do that. My thought was the Crouzet display has additional features built into it we don't need and by developing our own product we could reduce the size of the product by stripping away the functions we don't need. In the end we may end up taking the Crouzet apart and doing what you suggested but I want to explore the option to develop something that better fits our needs. If you refer to my previous post, I am considering the Lascar EM32-4-LED display. I imagine placing a normally closed momentary button to the lower left of the display that would reset the display to zero. Another normally closed momentary button would be placed to the lower right of the display which would switch the display between distance and speed. My hang up now is finding a microcontroller to perform these functions. Any suggestions would be appreciated.
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
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    I have a 4 digit LED display available, needs only 3 wires for serial interface.
    Soon also a double PCB for 2 displays.

    It is a low-cost display, $5.98 is for a single piece.

    Any kind of 4 digit LED display could be used.

    The displays only need 3V but can work from 2V to 5V.

    The larger PCB on the photo is used to flash the firmware to the serial display modules.
    Source code to use the display with a serial interface is here:
    http://pic.hitechworld.org/serial_led.html
     
    Last edited: Mar 19, 2013
  11. takao21203

    Distinguished Member

    Apr 28, 2012
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    You can use a 3V button cell with my displays, they will work a few days 24/7. A 9V battery typically also does not last much longer.

    Or 3.7V lithium CR123, these cells are also inexpensive.

    The microcontroller needed for the serial LED display can be nearly any controller, in the $1 to $2 range is good enough.

    The double display PCB I have available soon has some extra digital I/O, it is maybe possible to program all the functionality into it.

    0..999 is possible for 3-digits LCD. This is what they are originally intended for, 2x 3-digit LCDs.
     
    Last edited: Mar 19, 2013
  12. elec_mech

    Senior Member

    Nov 12, 2008
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    Hmm, if you're planning to go with a 9V battery, an LCD will last you you much, much longer power-wise. Assuming a horse is a sphere to make our calculations quick and easy, say 0000 is displayed all the time. That is 6 lit segments per digit, 4 digits total giving us 24 lit segments. Most LEDs will run at 20mA, but since this is a small display, let's say 10mA since it won't need to be too bright. That works out to 24 x 10mA = 240mA. In battery terms, this is 240mAh. A typical brandname 9V alkaline is roughly 565mA if memory serves, so you'll get about two hours of run time. This doesn't factor power required for the circuit or encoder, but I'm assuming those will be minimal in comparison. This is going to be the case for any LED display.

    If two hours of battery life is okay, then I'd suggest making the whole circuit from scratch - skip the Lascar EM32-4-LED. I'm not sure it is available for sale anymore and even if you find a similar product, I'm going to assume it runs $40 or more. Slightly less in quantities of 50-100, but not much. A small 4-digit seven-segment LED display is in the order of $6 each. Add a MAX7219 to make interfacing to a microcontroller (uC) at $11 in quantities of one, and you're under $20 for the display portion, even less in quantities. You'll still need to have a PCB to make wiring easier and to give you a way to mount the display to an enclosure.

    If you opt for the LCD, you'll probably have to settle for a larger (overall) display. This is simply due to the nature of LCDs, but you might find a tiny one. There are the ones found in digital watches for instance. Serial LCDs are more expensive and larger because they include electronics to make interfacing to a uC much, much easier. You can go hardcore and buy a standard LCD, but you'll spend hours designing a circuit and board for it, not to mention programming time. Looking at a serial display, the power consumption is 20mA, much better than 240mA, so a 9V could last over 25 hours as opposed to two.

    If you're going to dive into the wonderful world of uC's, you have to choose your uC and software carefully, software being the most important. Your choices are assembly (free), BASIC (free to $$$), or C ($5 to $$$).

    Assembly is a low-level language. It will require more time, effort, and intimate understanding of how the uC works. It will also require a lot more coding than the other two. Not worth the aggrevation to me.

    C is what I would call a mid-level language. It is much simpler than assembly and you can pick up a copy for as little as $5. There is a moderate learning curve though.

    BASIC is a high-level language. It has the shortest learning curve of all and requires the least amount of coding. Unless you're planning to make a living programming uC's, I'd stick with BASIC.

    I suggest using the PICAXE. I'm an ME myself and I started with Parallax Basic Stamp II's. While these are great, single IC's run $50. PICAXE's are $2-10 depending on the size of IC you need. Both Stamps and PICAXEs use the BASIC programming language, both free from their respective manufacturers.

    One important thing to note is these are both interrupted BASIC - think of it like giving instructions to someone who speaks another language through an interrupter. The job will get done, but not as fast as if you just did it yourself. For your application though, I think the PICAXE will work just fine. If you let us know your country, we can make suggestions for relatively local suppliers. For any uC, you'll need the IC as well as a programmer. For the PICAXE it's under $30 and you can use it to program all your chips. I just used a PICAXE for the first time here using a 4-digit, seven-segment display. You can take a look at this post and see what all is involved. Look specifically at post #'s 101, 112, and 115. The project was for a timer - since you don't need that, the DS1307 portion could be eliminated.

    Just know you're going to spend more time developing a circuit, PCBs, and programming than you would hacking the Crouzet. If you omit labor, the final price of the parts will probably be less for a custom solution. You'll have to determine which path is best. Hope this helps.
     
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