Fixing A Multimeter’s Serial Interface

[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.

Pokewithastick, an Arduino programmable web-logger/server


[Stewart] tipped us about his very nice project: pokewithastick. It is an Arduino compatible board (hardware, not footprint) based on the ATMEGA1284P which can be programmed to collect and post data to internet logging sites such as Thingspeak or Xively.

As you can see in the picture above, it has a small 50x37mm footprint (roughly 2″x1.5″). The pokewithastick is composed of an Wiz820 Ethernet module, a micro-SD card slot, 2 serial ports, one battery backed Real Time Clock (RTC), one radio connector (for the usual nRF24L01 2.4GHz radio), one power & user LED and finally a reset button. There are two power rails on the board which can be split (5v + 3.3V) or combined (3.3v only) which may allow you to connect Arduino shields to it. You can program the board using the standard 6-pin header or via a serial programmer if an appropriate (Arduino) bootloader is installed.

The project is open hardware, has been designed using Kicad and all the files can be downloaded as a zip file.

Stacking GPS, GSM, and an SD card into an Arduino shield

A few years ago, [Phang Moh] and his compatriots were asked by a client if they could make a vehicle tracking device for oil tankers all around Indonesia. The request of putting thousands of trackers on tanks of explosives was a little beyond [Phang Moh]’s capability, but he did start tinkering around with GPS and GSM on an Arduino.

Now that tinkering has finally come to fruition with [Phang]’s TraLog shield, a single Arduino shield that combines GPS tracking with a GSM and GPRS transceiver. There’s also an SD card thrown in for good measure, making this one of the best tracking and data logging shields for the Arduino.

The shield can be configured to send GPS and sensor data from devices attached to an I2C bus to remote servers, or a really cool COSM server. [Phang] is selling his TraLog for $150, a fairly good deal if you consider what this thing can do.

Seems like the perfect piece of kit for just about any tracking project, whether you want to know the location of thousands of oil tankers or just a single high altitude balloon.

Tip ‘o the hat to [Brett] for finding this one.

Data logging directly to Google Docs (Google Drive)

[Emanuele] is using Google Docs to log his temperature sensor data automatically (translated). We can see a few benefits gained by using this system. One is that you don’t have to visit the site of the logging hardware to harvest the data, another is that Google will automatically graph the data for you. Of course this means you need some way to connect your logger to the Internet, but we’ve seen buckets of different techniques for doing so. In this case, [Emanuele] is using PIC hardware that has a NIC on the board. But the technique could be used from a computer just as easily as from a microcontroller.

The meat and potatoes of the hack is sniffing out the HTTP header and syntax for writing to cells on a Google Docs (soon to be Google Drive) spreadsheet. After making a new spreadsheet and copying the URL and key from the address bar, he loads up the page using a header-viewer web service. With all the pertinent info in hand he crafts about a dozen lines of code to assemble the HTTP packet, and rolls the timestamp and temperature reading into it dynamically. See the system in action after the break.

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Unlocking RS232 serial comm on a multimeter

[Craig] cracked open a multimeter to unlock RS232 serial communications that can be used for data logging. There’s a couple of things that make this possible. First of all, the multimeter’s processor is not covered in a black epoxy blob, leaving the pins exposed for hacking. Second, the chip model is known and [Craig] was able to get his hands on the datasheet. One of the pins enables serial output when pulsed low. Touching it to V- even turns on an RS232 icon on the display, as seen above. To make this accessible without opening the case a momentary push button can be added, as well as connector for signal output, and a bit of parsing on the PC side to handle incoming data.

Tweetidor, the tweeting humidor

tweetidor12-300x225

As cigar aficionados will tell you, cigars should be stored in climate controlled humidors to keep them in best condition for smoking. Most of the time a humidor is just a simple air-tight box with a hygrometer attached, which measures the relative humidity inside the box. Feeling as though he needed more control over the environment he kept his cigars in, [Justin] created the Tweetidor, a humidor that tweets its current temperature and humidity. Yes, you guessed it; the project is built around an Arduino. It’s a simple, useful project that is well documented and would be fun to recreate if you’re into cigars (and not tired of Twitter or Arduinos yet.) Combine this with the laser lighter and you’ve got a pretty nice setup.

Tripmate gps data logger


This one is fitting – I was just checking out Suunto’s sweet gps data logging watches today. [Steve Cholewiak] sent in his diy GPS data logger. It uses an old DeLorme tripmate – these were serial gps units that ran off of internal batteries. A PIC controller reads the NMEA sentences from the tripmate. Then it stores the track data to an EEPROM. The same serial connection is used to retrieve the data later on. [Steve] did a great job writing this up, the circuit is pretty simple and he’s provided all the information you need to build your own.