Tagged: 3d printing

Monitoring 3D Printer Filament Moisture with an RTL-SDR and rtl_433

Over on Hackaday we've seen a post about Scott M. Baker's 3D printer filament drying farm that is monitored by a 433 MHz ISM band sensor and an RTL-SDR running rtl_433. If you're familiar with 3D printing then you'll know that it is critical to keep the plastic filament free from absorbing moisture, otherwise it can cause all sorts of issues when it comes time to print something.

To keep them away from humid air Scott uses "PrintDry" plastic vacuum canisters. Unfortunately he found that the vacuum sealing system wasn't perfect, and that some canisters would lose their vacuum after a few days. In order to ensure that the canisters were properly sealed he decided to add some active monitoring with pressure and humidity sensors and a wireless transmitter.

His monitoring system consists of a cheap 315 MHz ISM band transmitter, ATTINY85  microcontroller and pressure + humidity sensor. To receive and monitor the data he uses an RTL-SDR that runs the rtl_433 software, which is a program that is capable of decoding many different types of wireless ISM band sensors.

DIY Wireless Temp/Humid/Pressure sensors for measuring vacuum sealed 3d printed filament containers

A Discone Antenna Made from 3D Printed Parts and Aluminum Tape

A Discone is a type of antenna that is designed to be resonant over a wide range of frequencies. Most antenna designs only really receive well on a few resonant frequencies, but a Discone is resonant over a much wider frequency range. This makes it a good partner for RTL-SDR and other SDR units as many SDRs tend to have wide tunable frequency ranges. With a wideband antenna like a Discone connected to an RTL-SDR one can scan over the almost entire tunable frequency range without needing to change antennas for each band. The drawbacks to a Discone however is that the antenna gain is not very high, and that it makes the SDR more susceptible to out of band interference. They also tend to be fairly expensive and difficult to build.

However now over on Thingiverse, mkarliner (aka Mike) has a remedy for the difficulty in building a Discone with his 3D printable Discone design. To construct it you simply need the 3D printed parts, some .3mm and 2mm plastic sheets, a 25mm plastic conduit and some aluminium tape. Mike's design works from 400 MHz and up, but the design could be easily enlarged for better performance on the lower frequencies. He writes:

The Discone antenna is remarkable in that it is capable of receiving and transmitting over a wide range of frequencies with good matching. Because of this, it is a good match for SDR receivers such as the popular RTL-SDR sticks.

The only really tricking thing about making a discone is that the disc has to be balanced at the very top of the cone, which is mechanically awkward.

The two parts here allow the cone to be solidly clamped and provide an adequate base for the disk. There also two holes for bring the coax centre and braid out to the disc and cone.
The base part has a socket at the bottom for 25mm (1 inch) plastic conduit for mounting

This antenna illustrated is designed for 400MHz and up, and as such transmits well on the 70cms amateur band, US and UK PMR channels and 23cms. It also receives aircraft ADS-B signals very well. I used .3mm plastic sheet for the cone and 2mm plastic for the disc, and then covered them with aluminium weatherproof tape. Be sure to check for continuity across the tape stripes.

The screenshot is of a calculator by VE3SQB which can be downloaded from http://www.ve3sqb.com/ if you want to make attenna's for other ranges.

A 3D Printed Discone
A 3D Printed Discone

If you're interested in building wideband antenna there is also the planar disk antenna (pdf) which can be built out of pizza pans.

A 3D Printed Case for the DIY Outernet Kit

Thanks to Manuel (aka Tysonpower) for writing in and sharing his 3D printed ‘Universal Outernet Case’. Outernet is a satellite file casting service that uses an RTL-SDR based solution for reception. With an Outernet set up you can receive things like daily news, weather updates, books, Wikipedia pages and more all for free. About 20 MB of data can be transmitted in one day.

The DIY Outernet kit consists of an RTL-SDR ‘SDRx’ board, patch antenna and C.H.I.P single board computer. The patch antenna needs to point roughly in the direction of the Inmarsat/Alphsat satellite in your area. This can be a problem because the Outernet patch antenna doesn’t come with a stand or mounting solution.

Manuel solved this problem with his 3D printed Outernet enclosure. The enclosure houses the patch antenna, SDRx and C.H.I.P, and also doubles as a stand for pointing the patch antenna. Inside he’s also fitted a small 30mm fan to keep everything cool while inside the enclosure as the C.H.I.P is known to have overheating problems.

The 3D printed Outernet  enclosure.
The 3D printed Outernet enclosure.

Over on YouTube Manuel has uploaded a video explaining how the enclosure is made with 3D printing, demonstrates the assembly steps and finally shows the final product. The video is narrated in German, but it has English subtitles available. The design files required for 3D printing the case are also available on thingiverse.

[EN subs] Outernet Case aus dem 3D Drucker (Universal elv. Winkel) - für DIY Kit

A 3D Printed Stand for Generic MCX RTL-SDR Dongles

Thanks to Jaime (EB5ABT) for submitting his 3D printed stand for the generic MCX RTL-SDR dongles. The stand is designed to hold one of the generic dongles on it’s side so that a small whip antenna can be attached to it, whilst staying stably upright.

If you’re interested in printing the stand for yourself Jaime has uploaded the design files to his dropbox. He has also created a short YouTube video showing a slideshow of his stand which is shown at the end of this post.

If you’re interested in 3D printing accessories and enclosures for the RTL-SDR then thingiverse.com has a range of user submitted designs, ranging from custom RTL-SDR dongle enclosures, to stratux Raspberry Pi + dongle enclosures, to Outernet patch antenna stands.

Some of the RTL-SDR related design on Thingiverse.
Some of the RTL-SDR related design on Thingiverse.
Soporte receptor RTL-SDR