GPM8212 power meter rs232 header - Page 1
Forum section: electronics / testgear

author: beyondcrazy
author_rank: Newbie
timestamp: February 06, 2014, 11:17:35 pm
content: Hello,I picked up a used Instek GPM8212 power meter at a bargain price. Seems to be in excellent used condition, just doesn't have the rs232 plug on the back. The firmware appears to support it (even has the baud rate button on the front), and the cut out is already in the back panel for the 9 pin plug. I suspect the firmware is the same for both. Just needs the plug and wiring.I'm wondering if anyone has access to one that has the port installed. The plug doesn't appear to be an add-on kit on the web, and Instek says it can only be added at the factory.Upon internal inspection, it appears there is a 7 pin header identified as rs232. Maybe just a matter of wiring that plug to the right pins?Does anyone know if other rs232 enabled instek devices use a common header?Thanks!Jon

author: beyondcrazy
author_rank: Newbie
timestamp: February 07, 2014, 04:49:36 am
content: Here is a picture of the serial header from the main pcb.

author: SeanB
author_rank: Super Contributor
timestamp: February 07, 2014, 04:59:42 am
content: If there is a MAX232 or other serial driver set on the board (1488/9) then it will be a simple matter to get a connector and wire up the 9 pin D connector to it direct. You probably will have to look up where the TX and Rx pins are and connect those, and ignore the rest of the pins. There might be a small daughter board otherwise to do RS232 if there is a 5V pin on the connector though. With that you probably will be better off getting a USB converter and using the data off it direct to the header pins then. USB A socket fits in a D9 cutout with some filing and epoxy.

author: beyondcrazy
author_rank: Newbie
timestamp: February 07, 2014, 10:35:26 pm
content: Hi Sean,The power meter processor is an H8/3048. It does appear to use TTL, and a max232 would provide a proper interface.So, there probably is some sort of daughterboard that instek used. I traced the pins from that rs232 header, and the outside 4 pins pcb traces are thick, probably for power. The inside 3 traces are thin, and wired directly to the processor.So, I'm trying to find the wiring data for that chip, and then it should be easy to build an adapter to either use serial via rs232, or some sort of usb adapter as you suggested.

author: SeanB
author_rank: Super Contributor
timestamp: February 08, 2014, 04:57:59 am
content: Serial data pins are 12-15 on the FP100 package. So see which lines go to the socket, and likely you have a 5V rail and a +-12V rail to the power pins. Thus the interface is using a 1488/ 1489 serial driver set. If you get a USB-serial dongle with TTL outputs the data pins can go direct as they will be inverted data.

author: beyondcrazy
author_rank: Newbie
timestamp: February 13, 2014, 07:57:40 am
content: Hi Sean,I spent some time during the recent snow event in Oregon getting this sorted out.I found the wiring diagram for that chip, traced the lines, and determined that 4 of the 7 header pins were for power (2 ground, 2 5.0 volt) and the remaining 3 pins were for serial communications. Two were tx/rx, and a third for something else which I assume might involve rs485.I decided to try the rs232 route first, and found an adapter that actually uses that max232 chip. Very nice, mounted on a pcb, pin-outs for serial, and 3 leds for activity.I bolted it to the meter, wired it up, double checked the wiring, plugged in both the power for the meter and the power for the line-in, turned in on, and bam! popped the GFI breaker that powers one of the test strips on my bench.ugh... thought I messed something up. Some quick diagnosis reveals that if I plug in both power cables, it pops the breaker each time. If I plug in just one, it's fine. Traced it down to the rs232 adapter. Seems the ground pin for the serial plug pcb is also ground for the plug, not suprising. For some reason, it creates just enough leakage for the gfi plug to detect a problem when both power plugs are in. Ok, easy enough, I unbolted the plug from the chassis. It turned on, worked fine, until I plugged the usb end of the serial adapter into the usb port on the laptop, and it blew the gfi again.Sooo... an interesting problem. I've never seen a GFI act like that -- where a combination of all 3 plugs causes and issue, but any two are ok.On a positive note, I was able to get the serial communications working fine. When I powered just the meter and left the line-in plug off, the modification ran great. I was able to get the meter data to appear in the software. Just a matter of identifying the right pins.I'll post a pic here in case someone else is looking for the same functionality. I'm still trying to figure this GFI issue out though. I suppose it's easy enough to work around by using a regular circuit, but I am a little concerned about what is flowing through ground.

author: morrone
author_rank: Unknown
timestamp: September 06, 2014, 07:18:54 am
content: Do you happen to remember which pins were tx and rx?

author: morrone
author_rank: Unknown
timestamp: September 07, 2014, 07:31:35 am
content: For anyone else interested in doing this, I just go RS232 output working with my GPM-8212 as well.The pinouts, on the motherboard, starting from the end near where "RS232" is silk screened onto the board are:+5VGNDTXRXUNKNOWNGND+5VGiven the apparent leakage problems of the original poster, I decided to go with an isolating RS232 transceiver. The Linear Technology LTM2882 seemed to fit the bill, and it has a nice demo board already available. The demo board is the DC1747A-B demo board, which uses the LTM2882-5 (5V version). A bit expensive from mouser and digikey, but I found it for $25 US on ebay. Quick and easy.After wiring it up and then connecting to a computer using a USB-to-serial cable, I used picocom under linux to connect. It works! I found that the commands need to be issued at full speed to get a response. Typing by hand isn't quick enough to have the GPM8212 respond. I used cut-and-paste to issue the commands. For real use I'll just whip up a python script to do the logging.