Panel Meter takes 2V input instead of 200mV?? - Page 1
Forum section: electronics / projects

author: robobits
author_rank: Newbie
timestamp: April 26, 2012, 06:50:31 pm
content: I purchased a couples of CX101BG panel meters from futurelec, but when I received them I couldn't get them to read beyond 200. Once I removed the divider network the meters started working correctly.I lashed up the breadboard as shown in the first attachment. It pretty clearly shows a simple divider from 5V to ground and 1.66V being fed into the Panel Meter directly.I then popped open meter itself (attachment 2) and there are a bunch of spaces for resistors.So a few questions:1) Has anyone seen this before? I've never seen mention of one of these panel meters coming stock for a range of 0-2V2) Is it possible that the manufacturer didn't finish these two units and the missing resistors are the cause?I've never used these panel meters before, so I'm really curious if this is a manufacturing defect, or if this is something in the way in which I've ordered these meters and this 0-2V range is really a stock item.If anyone has one of these meters and could take a picture and post it back I'd really like to know if those resistor pads are supposed to be populated.Thanks,Kevin

author: robobits
author_rank: Newbie
timestamp: April 26, 2012, 06:56:38 pm
content: Just realized in looking at the pictures that the picture doesn't show a jumper between pins 5 and 8 on the panel meter.The meter is wired as followsPin 1 - 5VPin 2 - GroundPin 3 - NCPin 4 - NCPin 5 - To Pin 8Pin 6 - GroundPin 7 - Vmeter (at 1.667V)Pin 8 - To Pin 5Pin 9 - To Pin 10Pin 10 - To Pin 9Pin 11 - NCPin 12 - NCPin 13 - 5VKevin

author: DavidDLC
author_rank: Frequent Contributor
timestamp: April 26, 2012, 08:57:38 pm
content: You can set the input range by changing a resistor.I have some panels that support 200 mV, 2 V and 20 V, but I need to set one resistor certain value.David.

author: amspire
author_rank: Super Contributor
timestamp: April 27, 2012, 12:15:00 am
content: In general, it is best not not to modify the meter's PCB with new divider resistors. The reason is if in the future you need to replace the meter, it is nice if a new one will plug straight in. People tend to expect a device like a panel meter to work to the manufacturer's specification.When you say you had to remove the divider network, what did you have to remove? Did they provide the optional plugin divider board along with the meter, or did you have to remove components?Richard.

author: robobits
author_rank: Newbie
timestamp: April 27, 2012, 02:15:36 am
content: I have not modified anything on the meter. It is stock, as I received it from the vendor.When I initially set up my circuit I was measuring across a 2V drop so I put a 10:1 resistor divider between the 2V and the meter so that I would be feeding in 200mV max to get the reading of 1.999.These meters (I purchased 2) seem to be pre-configured for 2V instead of 200mV which is what I was expecting.I realize I can support 2V or 20V by adding resistors, but I'm surprised that I get a reading of 1.667 on the meter when I apply 1.667V to the input directly. I thought the range at the meter always had to be less than 200mV.There is no removable plug-in board that I can see and I did not modify the meter in any way.That's why I'm asking the question of what these meters normally look like on the inside. I think the manufacturer may have not completed these assembly's correctly, or I simply didn't realize that I was ordering a meter that was already configured for up to 2V instead of 200mV.Thanks,Kevin

author: amspire
author_rank: Super Contributor
timestamp: April 27, 2012, 03:08:11 am
content: I agree. It should be a 200mV meter. Sounds like you were sent the wrong version of the meter.

author: IanB
author_rank: Super Contributor
timestamp: April 27, 2012, 03:23:10 am
content: As far as I can tell meters like these may come preconfigured for 200 mV, 2 V or 20 V full scale. They also seem to have a jumper setting that can move the decimal point to various positions on the display. I am curious what level of standardization there is in these meters? Is there any kind of common convention, or is it the luck of the draw? (If you buy a meter from an electronic surplus supplier you may have no choice over exactly what you get.)

author: robobits
author_rank: Newbie
timestamp: April 27, 2012, 02:34:11 pm
content: And that is really the heart of the matter. How does one tell? There are no markings on the meter itself and the box and datasheet are both marked CX101BG (at least we know it's the common ground version).I wouldn't consider Futurelec a surplus provider so it shouldn't be luck of the draw.Kevin

author: saturation
author_rank: Super Contributor
timestamp: April 27, 2012, 02:55:08 pm
content: Yes, panel meters can be a PITA, since often the documentation is very poor.Luckily, there is a "defacto" standard, the PM 128A and variants, models B, C, at last count E.http://www.mpja.com/3-1_2-Digit-LCD-Panel-Meter-Multifunction-PM128E/productinfo/16177+ME/They are pop in replacements, and they are basically mini DMM. DCV, ACV and ADC. Differences in the old variants are no mA, no AC, no common ground. Some are made better or worse than others [ in terms of longevity, and clarity of the LCD.] but if you've worked one, you can figure the others out too.

author: J4e8a16n
author_rank: Regular Contributor
timestamp: August 24, 2012, 01:42:59 pm
content: Dont forget to let us know if you find out how to make it work with a shematic.JP