You probably know that to transfer the most energy between a source and a load their impedance needs to match. That’s why a ham radio transmitter needs a 50 ohm antenna (at least, usually). The transmitter is 50 ohms and you want a match. Some test equipment matches impedance, but for multimeters, oscilloscopes and a lot of other gear, the instrument just presents a very large impedance. As long as it is much larger than the measured circuit’s impedance, the effect will be small.
With today’s MOSFET instrumentation amplifiers, it isn’t uncommon to see very high input impedances. However, you sometimes run into something that has a low input Z and that can cause issues if you don’t account for them. On the other hand, where some people see issues, others see opportunities.
Continue reading “Data Logging in the Picoampere Range”
We ran into [Paul Allen] at CES. He was showing off Sigzig, a super-low noise data logger which his company is just rolling out.
A couple of years ago he worked on a standalone chemical sensor and had a few extra boards sitting around after the project was done. As any resourceful hacker will do, he reached for them as the closest and easiest solution when needing to log data as a quick test. It wasn’t for quite some time that he went back to try out commercially available loggers and found a problem in doing so.
The performance of off-the-shelf data loggers wasn’t doing it for [Paul’s] team. They kept having issues with the noise level found in the samples. Since he had been patching into the chemical sensor PCBs and getting better results, the impetus for a new product appeared.
The flagship 24-bit 8-channel Sigzig samples 0-5v with less than 1uV of noise. A less expensive 4-channel differential unit offers 18-bit with 10-12 uV of noise. They are targeting $199 and $399 price points for the two units. We asked about the sample rate in the video below. The smaller version shown here captures up to 240 samples per second. The big guy has the hardware potential to sample 30,000 times per second but
since the data is continuously streaming over USB that rate is currently limited to much less.
Update: It has been pointed out in the comments that USB may not be the choke point for sample rate.
[Husham] not only likes his electronics projects but clearly enjoys documenting them as well. He’s written a nice Instructable on a Temperature Data Logger that he has built and thankfully makes his code available for others to use. The end product is cleanly designed and made for weather-proof outdoor applications.
As you may expect, the brains behind this operation is an Arduino. It is coupled with a Real Time Clock to maintain accurate timing as well as an SD Card Module which is used to store the data collected. In this case, the temperature is read by a LM35 temperature sensor and that value, along with the time, is recorded to a .csv file on the SD card in one minute intervals.
There is also an LCD screen that displays the date, time and current temperature. To save battery life the LCD backlight is normally off. It can be turned on using a magnet that interacts with a hall effect sensor on the top of the case. This worked so well that [Husham] installed a second hall effect sensor on the side of the case that resets the Arduino. Speaking of the case, it is a weather proof PVC electrical box with a conduit adapter installed on the bottom side. A battery pack made up of two used laptop cells housed in a piece of conduit supplies 7.2 volts to the Arduino and other components. Unfortunately, there’s no word on how long the battery pack lasts. Once the data is logged, the SD card can be removed and the .csv file opened in spreadsheet software to make a graph showing temperature change over time.
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.
If you want to see what kind of abuse you’re causing your body when out on those single-track rides this system is just the thing. It’s an Arduino data logger that [Wdm006] takes along on the rides with him. When he gets back home, a Python scripts captures the data dump and graphs it. It may sound like a neat trick, but he’s got something planned for that information.
The enclosure mounts to the stem of his bike. It houses an Arduino board with a data logging shield of his own design. That shield holds an SD card for storage, and breaks the other pins out as screw terminals. Right now there’s an accelerometer on the front fork, and some method of recording wheel speed. This is the research phase of an anti-lock brake system (ABS) he plans to build for mountain biking. No word on what hardware he’ll use for that, but we can’t wait to see how it comes out.
[Willem] has a friend that wanted to take a GPS datalogger up an unclimbed mountain the wilds of Kyrgyzstan. The GPS logger built for the expedition made it to the summit of Eggmendueluek, but it didn’t work the whole way up. Since the logger came back to London, [Willem] was able to do a complete teardown and failure analysis.
The data logger was built around a Jeenode with a GPS unit and MicroSD card reader added on. A few breakout boards were made and two of these bad boys were ensconced in water and dust proof enclosures. Powered by four AA batteries, the data loggers were able to handle the rigorous testing of being thrown down a staircase and also the harsh temperatures of London. Things changed in the wilds of Kyrgyzstan, though.
The data retrieved from the mountaineering expedition wasn’t the greatest – a few wires came loose after being thrown into the back of a Russian truck and jostled around. The AA batteries only powered the data loggers for three days, compared to the 12 day battery life in London. There are a few improvements needed for the next trip – some thermal insulation and not using solid core wire – but not that [Willem] has figured out the bugs he’s ready for his friend’s next expedition.
The Arduino platform should be perfect for throwing together a lightweight webserver because of the availability of quality shields that take care of the hardware for you. As [Ovidiu Predescu] found, there are a few hiccups along the way and he’s put together a guide that covers the workarounds. Specifically, using an Ethernet shield and data logging shield at the same time produces a bus conflict which he sidesteps by cutting the CS pin trace on the data logging board and moving it to a different pin. There is also a bug with one of the chips on the Ethernet shield that is fixed using a similar method. So if you’re not just going to etch your own webserver hardware maybe this is the next best thing.