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Ignorant beginner looking for a start

Discussion in 'General Electronics Discussion' started by DGunthert, May 21, 2014.

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  1. DGunthert


    May 21, 2014
    I've got an Endless Pool set up on my back deck. For those that don't know, it's basically a treadmill for swimming. You can change the speed of the current using a remote key fob. The receiving board has an RJ-14 jack for output that allows you to hook up a pace display that gives a rough estimate of your pace per 100 meters. The downside is the display is $150. Seems a bit steep to me for what it is. I don't really care about what the alleged pace is. I wouldn't trust that it was accurate anyway. However, since I do increase and decrease the speed of the current quite a bit as I warm up and do intervals of different intensities, I'd like a way to return to the same speeds consistently.

    Keep in mind the subject of this post. I really don't have any idea what I'm talking about from here on out.

    The circuit diagram for the controller shows the wiring for the RJ-14 jack. Pin 1 is 24 COM, Pin 2 is 4-20 mA OUT. Pin 3 is 4-20 mA COM. Pin 4 is 24 VDC. I measured the voltage across pins 2 and 3. At the lowest speed setting possible, it was 1.238. As I increased the speed, the voltage increased pretty steadily by about .029 volts. All I really want to do is hook up a display that will show that voltage. That would be good enough.

    I only need something that shows voltage in the single digits and has 2 decimal places. I'd like something at least a couple of inches high so I can see it relatively easily from the pool. Obviously it has to work off the power output available through the jack. I don't know if I should have a preference for LCD or LED. I have no idea what else I should be saying or asking. Anyone have thoughts, advice, or display options?
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Welcome to our forum.

    From the description of the RJ-14 jack I guess the pin's functions are:
    Pin4 -> Pin 1 = 24 V DC (Pin 4=positive)
    Pin2 -> Pin 3 = current output 4mA to 20mA

    A ´current output is meant to deliver a controlled current (not voltage). So you should set your meter to 0-20mA DC current measurement.

    From that point on: do you realize that you already have the display you want at hand?
    This is what you need, isn't it? Buy a (very) cheap multimeter and hook it up permanently to measure the current from Pin 2->3.
    There you go.
  3. DGunthert


    May 21, 2014
    You're right, what I was measuring will suit my needs. I'd rather have something that's powered using the 24V supply that's on pins 1 and 4 (I'm assuming that's what the OEM's display uses.. I also want to make it fairly permanent and weather proof. I haven't had much success finding a display that would meet the requirements.

    Scratch that, I think I just did. Sanity check please:

    Measure range: DC 0-100V; Power Supply: DC 4.5-30V
    Permissible Error: 1% (+ / - 1 Digit)
    Display: three 0.56 " LED digital tube
    Display Color: RED
    Refresh rate: about 500mS
    Current consumption: about 5-20mA
  4. shrtrnd


    Jan 15, 2010
    What you're looking at is the power circuit to the board; and in the U.S. anyway, the separate industry standard 4-20ma signal control loop.
    There are oodles of readily available digital displays available that will show you that industry standard (industrial) 4-20ma signal in any format you want:
    incuding the 4-20ma, 1-5VDC signal you want to see.
    Google Red Lion, Omega, or a dozen other signal loop conditioner manufacturers.
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