Velleman PMLED connections

Discussion in 'General Electronics Chat' started by doug3460, Jul 5, 2009.

  1. doug3460

    Thread Starter Active Member

    Oct 19, 2008
    Hi all -

    Apologies if this is a total newb problem, but I don't want to ruin the meter. Trying to upgrade to an LED panel meter on my power supply but am having a bit of a problem understanding the instructions. Spent a couple hours Googling it, but can't find anything other than the instructions I have in hand. In order to set the meter for a specific max voltage & to set the decimal point, the directions read:

    To set the proper voltage divider:

    "Disconnect wire jumper in RB.
    RB = 9.9MΩ; RA = 100kΩ."

    To set the decimal point:

    "Short-circuit P2 - P0"


    I don't see any "wire" in RB. There are SMT resistors in RA & RB. The solder holes for the shunts are above & below them, so it's clear where to solder in the new resistors. But am I to remove the RB SMT resistor? There is a track line visible beneath the surface of the PCB that runs from the bottom solder point up into RB, but it doesn't make sense to me to have to cut the board.:confused:

    There is nothing on either side of the board labelled "P0." P1, P2 & P3 locations are clearly marked. P1 has a thick solder bridge in it already. Is "P0" unmarked because it is the row of solder pads below the labeled ones? Do I just connect a jumper in the P2 slot?

    Thanks for any assistance.

  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    Can you provide a link to any online documentation for the unit you are using?

  3. doug3460

    Thread Starter Active Member

    Oct 19, 2008
    hgmjr wrote:

    This is from the Velleman site & is a duplicate of what came with the meter.

    Unfortuneately, there are no drawings or photos. I can take a photo of the unit if you think that would help.
  4. Wendy


    Mar 24, 2008
    They hint there is a manual somewhere. What is the specific model you bought, and whom did you buy it from? I suspect pictures would be good, since they don't seem to care.
    Last edited: Jul 5, 2009
  5. doug3460

    Thread Starter Active Member

    Oct 19, 2008
    Bill_Marsden wrote:
    Hi Bill...yeah, they hint about a manual, but it's only a sheet of paper with the info that's shown on the link I posted before. The model is "PMLED". It's the 9V version (they also make a PMLED 5Volt version, & they have LCD versions). I got it from my local electronics supplier (34 miles away & not open on Sundays, before that suggestion is put forth, lol). I've attached a photo of the back - RA & RB are on the right side & the P jumpers are centered bottom. The glare area at the top is obscuring a couple SMT resistors & isn't associated with the stuff mentioned in the instructions. The front of the board only has the 4 7-segment LEDs, no SMT items or jumpers, etc..


    This can't be too difficult since they are so common. I even researched similar units from other manufacturers & sure enough, they use different terms but the shunt resistor numbers are identical as those given for this unit & so are the instructions for the decimal selection. And none of them actually show pictures/drawings of what they specifically are referring to. Personally I suspect they are ALL made in one place, then different labels/packaging slapped on 'em, lol, since we all know that happens :rolleyes:.

    Anyway, I just didn't want to undue the RB SMT resistor if that isn't what they mean (I can get it off the board, but putting it back could be a challenge :eek:).

    Thanks for any help.
  6. Wendy


    Mar 24, 2008
    Lower left is the battery, which is a start.

    The resistors have solder holes, I'm bettin they intend to jumper around them with wire, but it is optional.

    Lower right, the pins, are they labeled + and -? The shadow obscures the potential markings.

    P1 is jumpered, you can remove it, and put a jumper on P2, or P3.

    So the question in my mind is how RB and RA is handled. It looks like they are meant to be jumpered, but I'm going to see what other ideas are out there.


    Rereading the instructions, they want you to add the resistors in the holes provided, marked Ra and Rb. The resistors are not there.
    Last edited: Jul 5, 2009
  7. doug3460

    Thread Starter Active Member

    Oct 19, 2008
    Here's the answers to my original questions (based on a board that looks like or similar to the photo I posted:
    Regarding the SMT RB resistor: SMT resistors marked with a "0" are wire jumpers. Remove it as the directions indicate when you are adding new resistors to create a new voltage divider.

    What the instructions don't indicate is also remove RA. Failure to do so will result in the wrong value when you add the new resistors.

    Regarding the decimal point jumper "P0" connection: The "P0" row is the row beneath the labeled ones for the decimal point.

    What the instructions don't indicate is remove any other jumper there when you add a jumper to select a different decimal position.

    One other clarification. As Bill pointed out in his reply, one set of connection pins has a battery symbol. This is for the supply. On my board, the battery pins are also labeled V+ & V-, & the labels for the other connection pins are IN+ & IN-. When I read the instructions, I misunderstood this line:
    "Connect the voltage to be measured to Vin+ and Vin-."
    I should have caught it, but didn't & fried the IC when I reversed the connections. lol. The instructions do mention to watch out for polarity, but they don't mention to watch out for having the correct polarity attached to the wrong set of pins! :eek:

    Oh well, I'm now familiar with the 7106 (for LCDs) & 7107 (for LEDs) A/D drivers. It appears Velleman uses different manufacturers for their chips, but the chips themselves appear to be interchangeable according to most of the datasheet pinouts. I used an Intersil 7107 to replace the original Hitachi that I cooked. The 9V supply also doesn't seem to be presenting a problem either, even though all the datasheets I found for the 7107 indicate a ±5V as the supply at the pin connections for the chip power. The datasheet even shows how to make a simple negative line breakout from a single supply with just a few components. I don't know why I was able to simply replace the chip & not change the supply voltage, but I did & it's working fine. I tried comparing the datasheet recommended parts list with what is on the PCB & it appears straight forward in both component value & parts count - couldn't find any additions indicating some sort of breakout of the ± voltages. I'm using a 7809 regulator to supply the meter power, not a battery, so I know it's not due to a voltage drop from the source. I have had it on for awhile now to ensure there weren't problems. The meter is working as advertised so I'm not inclined to try to "fix" it. Yet. :D

    Hope this helps someone down the road.
  8. Wendy


    Mar 24, 2008
    Coolness. I've looked at those meters myself with an eye to using them.

    Wonder how long it took to find the incompetent sadist to write the manuals.

    It's always nice when someone volunteers to be the polish mine detector.
  9. montytim

    New Member

    Aug 9, 2010
    I bought one 129A for use with a shunt for measuring current and another for measuring voltage, RV application.

    The circuit board is marked "PM-129A-3".

    The default as-manufactured surface mount resistors RA and RB are 10 megohm and 0 (shorted) respectively. This is for 200mV range.

    Note that RA is the resistor in the voltage divider that is being sensed, not RB. (Obvious from the default resistor arrangement)

    What this means is the datasheet that comes with the device is wrong. The smaller value resistor goes in position RA.

    As noted above, both RA and RB surface mount devices need to be removed if you are changing the range to other than 200mV.

    Hope this helps.
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
    Don't get me going on some of the funniest readings I've had over the years. I remember the replacement instructions for one part went on for 13 steps then #14 appeared as "First, before do anything, please to ..."