LVL1 has a new rocketeering group. This rocket engine testing platform is the first project to come out of the fledgling club. The purpose of the tool is to gather empirical data from model rocket engines. Having reliable numbers on thrust over time will allow the team to get their designs right before the physical build even starts.
The rig uses a pine base, with a PVC frame, threaded bolts, and a PVC cuff for mounting the engine in place. It is set to fire up in the air, directing the thrust down onto a scale. The flex sensor in the scale is monitored by an Arduino, and should be able to hold up to the 5000
pounds grams of thrust max which this type of engines can put out. The data is pushed via USB to a laptop computer where it is stored in a spreadsheet.
Calibration would be an issue here. But as long as they’re always using the same strain sensor the numbers will be accurate enough relative to each other.
[Casainho] wanted to track his body weight using an app on his Android phone. He just needed a way to get the weight readings onto the device automatically. He ended up adding Bluetooth to a bathroom scale and hacking the app to grab data from it.
The scale which he hacked is a digital model, which makes it possible to read the weight data if you know what you’re doing. [Casainho] already completed a weight logging scale hack which stored the data on an SD card. So this was a recreation of that project but with a Bluetooth module for the output rather than the card for storage.
Now you can buy WiFi enabled scales, but that’s not nearly as fun as a hack like this. Plus one of those will cost you around $200 and the hardware for this version came it at only $75. It includes an LPC2103 dev board, $6 Bluetooth module, character display, batteries, and misc. supplies. The software end of the hack was helped greatly by the fact that the Android apps which [Casainho] is using are both open source.
[MakingThingsWork] wanted an accurate way to keep track of the weight of his beehive, so he decided to build himself a data logging electronic scale. First he ripped the strain gauges from an old electronic scale which he then fitted to his home made beehive base. He then went about designing and building the control board which is based about the Attiny 85 (if you hadn’t guessed by the banner). An instrumentation amplifier was used to amplify the signal from the strain gauge, which is then read by the ADC on the Attiny. It looks like he had some trouble getting consistent results from the scale, so to eliminate the error caused by temperature variations he set up a fixed voltage divider for reference. With this setup the scale can produce results at +/- 0.5lb accuracy, sounds just fine for a system that cost less than $50. The V-usb project software has been used to connect the scale to his PC which he uses to collect and graph the data. All in all a very neat project and by the looks of it, some very productive bees.
[joe] wanted to make it easy to record his weight every day, and added a few bits to decode the weight and send it to his computer. The end result is a ZigBee-powered wireless scale. Additionally, his scale can track more than one person’s data simply by knowing whose previous weight the new measurement is closest to. Now [joe] and his family can spend more time working out, and less time messing with spreadsheets and data entry.
[joe]’s build is not only elegant, but well-documented, too. He walks through the reasons he chose this specific floor scale, reverse engineering it to decode the weight, then provides links to his schematics, source code, and pretty much everything else you would need to play along at home.
Above you see a solenoid being used as a digital scale. The magnetic field from the coil in the base levitates the platform above, where a load to be measured is place. This floating platform has a permanent magnet in it, hovering above a hall effect sensor in the base. As the distance between that magnet and the sensor changes, the measurable magnetic field changes as well. The hall effect sensor is linear so the measured value can easily be correlated with a weight. In the video after the break [Vsergeev] demonstrates the device using test weights to show off its 0.5 gram resolution. He thinks that with a few hardware improvements he could easily achieve 0.1g accuracy.
Continue reading “Magnetic digital scale”
Did you know weighing bee hives was even necessary? Of course it is. Monitoring hive weight can tell a beekeeper a lot about the size of the swarm, their harvesting habits, and the yield they are producing.
We had to cover this hack because it’s a fine piece of engineering. [Trearick] designed a bee hive scale that lifts one side of the hive to calculate weight. Using easy to find metal brackets, a hinge, a pulley, and some plywood he built a prying device. The three teeth slip in between the hive and its base and can be separated by squeezing together the plywood handles on the opposite side. This lifts one end of the hive, measuring the force needed to do so using a luggage scale. The readout should be roughly 1/2 the total hive weight. This measurement takes seconds to complete, uses a bulb level on the scale to help ensure consistency, and creates little or no disturbance to our flying friends.
It’s nice to see a Hymenoptera hack that helps in giving bees a healthy place to live, instead of killing wasps.
[Micah] was inspired by projects he had seen of people using the Wii balance board as an input. He realized the balance board was overkill, and pricey for many applications. Since it is basically just 4 weight sensors, he thought, why not just use a scale? Often, only one sensor is needed and they’re really cheap from big box stores. He picked up a digital scale and cracked it open. As he moved forward, he wanted to keep this pretty simple. There are other ways of getting the information from a scale, but they have been generally more complicated than what he had in mind. He ended up bypassing the internal unknown microcontroller and just connecting the analog sensors to his parallax setup. You can read all about the process an download some source code on his site.