generic LED voltage panel meter has tx/rx connections?

I picked up a small, generic LED panel meter and quickly found a use for it so I ordered another one from some random ebay seller, and when it showed up I threw it in a box. I recently pulled it out for another project and noticed one of the wires pulled out. As I was soldering them back on, I noticed that there was a row of solder connectors on the other side, and three of them were marked with tx, rx and gnd.

I can't seem to find any kind of a model number on this thing and haven't had a lot of luck in finding any kind of spec sheet on these things. Does anyone have any idea what the tx/rx connectors might be for on something like this? (it would be nice if I could get a sensor-like reading of the voltage out of one of these things in addition to the display!)

Here's a sample auction of one that has the same kind of connectors on the back:

Tre`

What's underneath? I'll bet the jewlery is on the side of the board covered by the LEDs, so unless you find someone here with information, you'll likely have to sacrifice one in the name of reverse engineering.

If the part number is still on the IC, you might be able to figure out what it's doing.

My guess is they used that to program an internal microcontroller... and/or maybe it's outputting measurements on that. Put a 'scope on them, see if any of them are outputting anything.

I have some buck regulators that have a daughterboard on top with voltage and current displays. On it, the pins labeled TX and RX are connected to the hardware serial port on the microcontroller on that daughterboard.

In the Amazon reviews of this switching regulator, I found a comment that details out how to query the RX/TX connections and get serial data out to get mA and mV precision out of it. FYI, the LED readout is only good to two decimal places, so 10mA granularity.

Quoted here in case anything happens to the link above:

Travis C Hayes says:
I was also a bit disappointed not to get milliamp precision on the LED display. Digging a bit further, the TTL serial interface (see the labeled product picture) can be queried to report mV or mA.
To query current, configure serial for 9600 8N1 and send:
char req[7] = {0xbb, 0xcc, 0x00, 0x00, 0x00, 0x00, 0x00};
and you’ll get back a 6 byte response like:
res = {0xbb, 0xcc, 0x00, 0x00, 0x59, 0x23};
int milliamps = res[5];
milliamps = (milliamps << 8) | res[4];
For my application, figuring out serial querying of this board supplied what I needed. Goodbye voltage divider, current sensing resistor, and spend a UART to save two analog inputs on my microcontroller.

Perhaps your board uses a similar method?

treii28:
I can't seem to find any kind of a model number on this thing and haven't had a lot of luck in finding any kind of spec sheet on these things.

Something about porcine avionics comes to mind. :roll_eyes:

treii28:
Does anyone have any idea what the tx/rx connectors might be for on something like this? (it would be nice if I could get a sensor-like reading of the voltage out of one of these things in addition to the display!)

They are not connected. I though it would be nice if they output serial data - but they don't when I checked. :slightly_frowning_face:

Yeah I need some spare time to figure out how a scope even works. I picked up one of those pocket ones shaped like a small cell phone but have never really used one before so I'm wallowing any time I pick it up.
And yes, the electronics are under the LED

I'll check out the amazon link but I notice the last post seems to know it might not do anything. I was just curious just in case. Thanks for the info.
I'll report back if I find anything.

That DROK board doesn't appear to be the same one I have, so I doubt it's relevant, but I may pick one of those up as I'm building a power box (That's why I was pulling out the voltage panel display to begin with. I managed to pick up two nice 12v deep cycles and a 75-100A blade-server power supply during the same 2 week period of hamfests and craigslisting. So I'm going to hook my solar panels up at home when I'm not using them camping. I'll make the box take a single 12v input that can come either from the batteries or the power supply and I'm going to be adding 9v, 5v and 3.3v buck converters inside. I already let the 'magic smoke' out of my 10A buck converter unfortunately that I was planning on using for the 5v drop - new one on the way. I guess next time I temporarily put a tender-SAE connector on backwards, I damn well better clearly mark it so I remember it was just a temporary hack)

I also picked up a 4 relay arduino shield that I'm going to slave to my new RPi 3b so it can remotely turn on/off previous 4 pis as needed. I split up various tasks among them, but seldom need the others since the new 3 is beefy enough to handle the important stuff.

I have only one suggestion for you:

Take notes.

It would be advisable to take notes for every project and keep a notebook and a file of manila file folders, each with the name of the project or device. In this case ALL the documentation for your mysterious module would be in that folder.

Wow, someone's sphincter pucker is tight. I keep notes in my program code when I actually find something worthy of building. It's called documentation.
And I did google it, found nothing. I don't have my internet computer on my soldering bench and had more than just the panel meter to work on with the aforementioned project under way. So I didn't get around to googling it until I got to work the next morning and generally don't bring sundry electronic components with me to work. But after I found nothing on google, and got no help from two of my friends who work with electronics, I figured I would post on the forum so someone familiar with it might be able to chime in by the time I got home and had a chance to get at it again. To be thorough, I then included a link to a source with a photo that had a close-up of the tx/rx pins.

So what the @#$ is your problem?

I guess every forum needs at least one over-the-top protocol nazi.

So what the @#$ is your problem?

I guess every forum needs at least one over-the-top protocol nazi.

You know, I've been called a lot of things here on the forum, but I think you're the first to actually nail it.
Yeah, protocol nazi, that would be me. ;D

FYI,

As I was soldering them back on, I noticed that there was a row of solder connectors on the other side,

The correct term is "through-hole solder pads" (="solder connectors").
They're not called solder connectors because the word "connector" , in electronics, means some "thing",
(as opposed to some "hole")

I then included a link to a source with a photo that had a close-up of the tx/rx pins.

They are not connected. I though it would be nice if they output serial data - but they don't when I checked.

It looks like Paul already checked those pins and they aren't connected.

Yeah I need some spare time to figure out how a scope even works. I picked up one of those pocket ones shaped like a small cell phone but have never really used one before so I'm wallowing any time I pick it up.
And yes, the electronics are under the LED

I suppose you could try your scope to see if there is anything on those pins.
If there had been , the following describes how one might read it. Since there probably isn't any serial data on those pins, you can disregard the following , unless you have nothing else to do and want to read it for future reference.

Good news/Bad news:

The bad news first:
The tx/rx pins of the meter are probably the interface between the meter circuit and the display circuit.
It's probably a microprocessor meter with a serial display. One way to find out is to solder a couple of wires to it and connect it to a PC running a terminal program. The bad news is your going to need to convert that to RS232 to connect it to a PC. Then you can run the terminal program and hopefully see the ASCII sent by the meter circuit to the display.

If you're the hacker type and have the patience and are up to the challenge, you , or your electronics friends (who weren't much help) can hack those three wires and connect them to a PC to see what's going on there.

The Good news: , that part should actually be easy.
Those holes look to be designed for a male header connector. You can use them to connect some 20 guage solid wire to plug into a breadboard.

You have two options:

Option-A: Order the ebay converter and make your serial cable to plug the DB9 of the converter to the DB9 of your PC. You'll have to experiment with all the different baud rates but I would try 9600 first.
I think we can assume the start bits , stop bits and parity are all 1.

Option-B: Buy a MAX232 chip and breadboard the converter circuit and make a cable with 20 guage solid wire at one end and a female DB9 at the other end and connect the RS232 side of the circuit to the PC with that custom cable. The TTL serial side of the chip would connect to the two wires + GND that you soldered to the back side of the PCB. If you had access to a scope, the first thing you would want to do is look at the signals on those pins to verify it is 5V TTL serial. Someone who really knows C++ could probably read the data but without knowing the correct baud rate that could be a tedious process of trying all of them. A terminal program is much easier because you just try everyone until you get to the right one and then the garbage turns into readable characters.

Do you have any terminal programs like Clear Terminal or Hyperterminal ?

The serial is probably TTL 5V level, not RS232 so you need some way to connect those pins to your pc or laptop but the problem is the DB9 RS232 connector on a PC is rs232 so you would need an RS232 to TTL SERIAL converter like this.

This converter has a femaie DB9. The PC has a male. if you can't find a male-female cable you can modify whatever you find by adding the appropriate male -male or female - female gender changer.
Don't waste any time trying to use an arduino to communicate with it. It can be done, but only if your specialty is software, particularly C++. It's much faster to just connect it to a PC and run a terminal emulation program. I have one called Clear Terminal, one called Real Term and one called Hyperterminal.
I'm running Win 7 so I don't have the Hyperterminal that everyone is familiar with from XP. There is a company that has a free download program called HyperTerminalÒ Private Edition 6.4
by Hilgraeve Inc., that does a pretty good job of emulating the XP Hyperterminal we're all familiar with.
I tested it and it works. You need to connect the tx of your lcd meter to the rx of your RS232 converter on the TTL side and the rx of your meter to the tx of the converter on the TTL side. Run the terminal program to see if there is any data on those pins. If you don't get anything you could try hitting the enter key to see if anything comes back. I seriously doubt those pins were intended for the end user to mess with so don't be surprised if all you wind up with is a serial output for your meter voltage.
Good Luck Mr. Phelps.
As always, should you be captured the Secretary will disavow any knowledge of your mission.
This tape will self destruct in 5 seconds.....

Something about porcine avionics comes to mind.

I think "When PIGS FLY !" sounds better ...(but that's just me)

I wouldn't call " notes in my program code" "documentation".
"Documentation is hard copy kept in an alphabetcally sorted file or copy kept in an alphabetically sorted folder of subfolders ;
ie: Meters/panel/ modules/7-segment

It sounds like you are saying all your documentaion is scattered through your program code files. What good is that if it is not all located in one central location ? I'm not seeing the usefulness of storing hardware reference documentation in software files. How could you remember which software file it was stored in?

Wallowing is bad. Don't do that. Post on this topic for the pocket scope with the vendor link.
I can name two senior members that have something similar who could probably help you.
That's the "protocol".

I would know, wouldn't I ?

re: “The correct term is “through-hole solder pads””

Thanks, I’ll make sure to right that down in my notebook right next to where I wrote 'bought from some random chinese guy" in regard to the panel meter details. Just so I can use it again - never.

There was another thread I posted recently. I can look it up if you like. It was one where I commented about how the amateur radio community is nothing but a bunch of old nerds now because there are so many hams that condescend or otherwise act pretentious to anyone curious about radio and they can’t seem to relate to everyday people anymore. However, I wrote that piece to comment on just how many condescending, pretentious %$#holes I seem to constantly run across when asking for EE knowledge. I wrote it for people like yourself.
I don’t think it was in this forum, and I won’t bother chasing it down or cross posting it because I doubt you’d read it anyway if it wasn’t in one of your precious notebooks. Wow.

Trying to get [young] people interested in electronic experimentation is hard enough without the lecture circuit volunteering all the time. But hey, I get it - you worked many many many years to accumulate the knowledge you have and you don’t like giving it away for free without it being properly appreciated. The problem is that what EE folks never seem to get is that for the rest of us, the minutia of what you do is not necessary for us 365.2499 days out of the year. Thus we have no interest in learning the finer minutia points of Ohm and Farraday and Watt down to the 12th decimal point - because we don’t have to.

TRe

Trying to get [young] people interested in electronic experimentation is hard enough without the lecture circuit volunteering all the time. But hey, I get it - you worked many many many years to accumulate the knowledge you have and you don't like giving it away for free without it being properly appreciated. The problem is that what EE folks never seem to get is that for the rest of us, the minutia of what you do is not necessary for us 365.2499 days out of the year. Thus we have no interest in learning the finer minutia points of Ohm and Farraday and Watt down to the 12th decimal point - because we don't have to.

"You can lead a horse to water, but you can't make him drink."

I think what you are trying to say is that young people today are growing up in a period where time seems to be going at some breakneck pace and there is no time to learn Ohm's Law before the world comes to an end. We old nerds, who have spent many years accumulating our knowledge , find that we have no problem solving all our electronics issues because our knowledge is built on a base fundamental concepts. Some of us, like myself (and I could name a dozen others) have 3 or 4 year degrees is electronics engineering which adds another dimension. The majority of the senior members have years of solid work experience that is just as valuable and often more so. We do not see the logic in pursuing electronics in a manner where you treat each project as a unique event and learn only what you need to get that working but not the basics that allow you to solve all future such issues. To us, that just seems , well, dumb I guess. I don't know what level to put that at but I would have to say it reminds me of the toddlers in my wife's childcare , where they relearn the same thing every day.

We are here to help you.
Insulting us isn't really the best approach to seeking help. Recommending you keep notes in a more organized fashion doesn't warrant insults, in my opinion. I don't recall using punctuation to to describe you. What may come as a surprise to you , is that instead of insulting you back (which would , after all be childish), I am telling you that you are still welcome to post here, but please refrain from insulting us when asking for help.

When you look at your post, it is clear you didn't really have any problem after all. You simply thought you could get more for whatever you paid for the module that apparently works perfectly and does what you expected. You didn't order it for the extra feature anyway.
Good luck with your approach to electronics. I think you are going to need it.

Thus we have no interest in learning the finer minutia points of Ohm and Farraday and Watt down to the 12th decimal point - because we don't have to.

Well if you don't know how to figure it out I guess we'll see you back here.

Trying to get [young] people interested in electronic experimentation is hard enough

Well, really, if you think about it, it can only be called "experimentation" if you don't know what you're doing. When we build circuits, most the time , we're not conducting any experiments. We decide we need a circuit, so we design it. We build a prototype and test it and based on the test results , we might make a few changes to the circuit but it would be more accurately described as prototype empirical testing than "experimentation" which suggests some experiment is being conducted. But in your case, I would suppose that it would be considered an "experiment " every time you do anything because you refuse to learn the basics and wind up just throwing stuff together without doing any math. Your post about the serial pins that aren't connected to anything is a good example. Did you bother to measure the voltage on those pins to see if there was any DC before posting ? If there is no voltage then it would seem they are not used in that version of the product and there is no point in pursuing it further.

You seem to know something about software. I read some of your posts and you seem to be a lot stronger in the software area. How do you feel about people who just cut & paste code together and post because they have no clue what they are doing and no interest in learning the finer minutia of software ?

This is getting quite entertaining. :roll_eyes:

+1

So much misplaced anger.

Hey, Paul__B, did you just connect a scope to those TX/RX pins, or did you try sending a query to it? The Amazon post I referenced seems to indicate that nothing comes out unless you send something to it, first.

polymorph:
So much misplaced anger.

Hey, Paul__B, did you just connect a scope to those TX/RX pins, or did you try sending a query to it? The Amazon post I referenced seems to indicate that nothing comes out unless you send something to it, first.

That was the same question I had - the comment about "it only talks when asked" seemed important. Be interesting if it does talk though!

And yes, I often keep most of my documentation about a simple project (or links to the data sheets) in my code. Yes, I worked for many years in avionics and am familiar with requirements documents (having helped write them too) as well as verification testing and requirements matrix databases where we link all the code to the requirements, test conditions and code modules (which is why it costs millions of dollars to change a line or two of code in either flight software or medical electronics - have a read of DO-178B if you are having trouble getting to sleep at night :o )

I should also add that when I create a schematic, I like to put text boxes on the schematic with important information such as decode addresses, functional information, expected test voltages etc. (I used to use "clouds", but they are hard to draw in Eagle - back when I did schematics with Mylar and plastic lead, we put clouds on the schematics. Since we were the ones that had to work on the circuits and debug things, it was handy having the information on the schematic (or in the code listing) instead of some folder on some computer somewhere.

At work I have folders for each "project".
Since a project could be anything from "build a test fixture" to "install smoke alarms above all the R&D test benches but 'hack' them so the 277V contactor shuts off when the alarm detects smoke using the N.O. relay contact on the alarm" ( FYI, there's 12 R&D benches) . Sometimes a project is run tests. Since the documentation could originate from the engineers (test plan/schematic of wiring changes to test equipment or it could be my schematic ( power distribution box wiring),
the way I keep it organized yet accessible to others is by scanning hard copies and putting all the docs in their own folder. I have a file cabinet with hard copies as well. I'm not a programmer ( I'm a H/W Electronics Engineering Tech so I don't have any code at work so your method wouldn't work for me. Besides, reference docs for me is not something that can be typed in. It's a schematic or an email with instructions and attachments. At home it's different because I have code , datasheets and schematics for everything as well as photos, which you can't put in code. I just create a folder for the subject and sub-folders for each type of document. That works at work and at home. The bottom line is "does your reference document storage and retrieval system work ? After reviewing all the information provided I concluded that the OP's problem was not related to the subject we are discussing but rather came down to " How can I find out if these two pins are functional and if so how can I use them. I spent a lot of time addressing that question but it was not appreciated. After reading Paul's post I thought maybe there's no traces going to those pads. Any TTL compatible circuitry would have had a voltage, at least on the Tx pin , if not the Rx pin.

Clouds ?
Haven't seen those in years.

Might not meaning anything.... but 30 seconds of google search came up with...click here

Might not meaning anything… but 30 seconds of google search came up with.

Can you post your Google search keywords ?

It doesn’t look like the same one but the communication setup instructions could be useful in the future.

On page 10 of that PDF file, it says:
“Before connecting panel meter board and USB-RS232 converter, find your 6-pin Dupont cable that comes with the package of ME-SPO37B. the construction of Dupont cable is as follows:”

On page 6 it says this:

PANEL METER MANUAL PAGE 6.jpg

It might mean something, but not to this post. (since it isn’t what the OP has)

raschemmel:
Can you post your Google search keywords ?

Sure can. They were "led panel meter tx/rx/gnd"