[Shane] bought a multimeter with the idea of using its serial output as a source for data logging. A multimeter with a serial port is a blessing, but it’s still RS-232 with bipolar voltage levels. Some modifications to the meter were required to get it working with a microcontroller, and a few bits of Python needed to be written, but [Shane] is getting useful data out of his meter.
The meter in question is a Tenma 72-7735, a lower end model that still somehow has an opto-isolated serial output. Converting the bipolar logic to TTL logic was as easy as desoldering the photodiode from the circuit and tapping the serial data out from that.
With normal logic levels, the only thing left to do was to figure out how to read the data the meter was sending. It’s a poorly documented system, but [Shane] was able to find some documentation for this meter. Having a meter output something sane, like the freaking numbers displayed on the meter would be far too simple for the designers of this tool. Instead, the serial port outputs the segments of the LCD displayed. It’s all described in a hard to read table, but [Shane] was able to whip up a little bit of Python to parse the serial stream.
It’s only a work in progress – [Shane] plans to do data logging with a microcontroller some time in the future, but at least now he has a complete understanding on how this meter works. He can read the data straight off the screen, and all the code to have a tiny micro parse this data.
[Mustafa Dur] wrote in to tell us about his hack to control the television with a smartphone. Now the one-IR-remote-to-rule-them hacks have been gaining popularity lately so we assumed that’s how he was doing it. We were wrong. He’s using his satellite receiver to provide the Internet connection. It pushes commands to his LG 47LH50 TV which has an RS-232 port.
The image above is the back of another LG television (it came from a forum post about controlling the TV with a PC). [Mustafa] is using a Dreambox DM800 satellite receiver which also has a serial port an he can telnet into it. He searched around the Internet and discovered that it should be possible to connect the two using a null modem cable. His initial tests resulted in no response, but a tweak to the com port settings of the box got his first command to shut off the television. After a bit of tweaking he was able to lock in reliable communications which he made persistent by writing his own startup script. From there he got to work on a Python script which works as the backend for a web-based control interface.
If you want to find out what else you can do with this type of serial connection read about this hack which used a script to try every possible command combination.
[André Sarmento] needed to connect a computer to an RS-485 bus. A simple converter can be sourced online, but the only thing he could find locally that was even close was a USB to RS-232 converter. He used that component to craft his own USB to RS-485 bridge.
RS-485 is often used for remote sensors as it provides a method of connecting electronics over long distances. The converter which he started with seems to be encased in a hot-glue-like substance. A bit of time with a torch and he was able to get to the components on the board. There are two stages, one which converts RS-232 to TTL, and the other converts TTL to USB. [André] removed the RS-232 chip and patched his own board (shown on the left) into its TTL lines. He was also able to add a few more configuration options, like using an external power source, and having a few jumper-selected resistor options.
If you’ve been amused by the lengths people go through to speak to a serial device these days. [timmeh] just took the cake. He build his own frikkin’ tiny RS-232 to USB interface with the diminutive SIL CP2101. The package on it is QFN-28 (If PLCC is Darth Vader, QFN-28 is his mean little brother.) That said, if you prefer to work with stuff that talks TTL or RS-232, this could be a handy add-on to pop a USB port on your project. (Oh, look, they have samples…) Sure, we’ve beaten the serial connections to death, but they’re so handy we just can’t resist. It may be a decent way to add a serial port to your laptop. (Picture this: dell’s bluetooth cards are usb devices – you could add one of these without even voiding your warranty.)
[Alan] sent me his simple rs-232 controlled power outlet. He built it to turn on his laser printer when a print job appeares in the queue. The relay is directly controlled by the DTR line on the serial port. Lots of espresso machine PID conversions use them to run boilers, so he could have avoided the extra mechanical relay. [I can’t pick on him too much, my old laserwriter is on all the time.]
He tied it together with some perl to turn on the printer and get the print job going once it’s had enough time to initialize.