315 MHz

2 Articles

Cheap Sensors And An SDR Monitor Conditions In This Filament Drying Farm

September 14, 2019 by 3 Comments

We don’t know where [Scott M. Baker] calls home, but it must be a pretty humid place indeed. After all, he has invested quite a bit in fancy vacuum storage containers to keep his 3D-printer filament dry, with the result being this sensor-laden filament drying farm.

[Scott] wasn’t content to just use these PrintDry containers without knowing what’s going on inside. After a little cleaning and lube to get all the containers working, he set about building the sensors. He settled on a wireless system, with each container getting a BME280 temperature/humidity/pressure sensor and an SYN115 315-MHz ISM band transmitter module. These go with an ATtiny85 into a compact 3D-printed case holding a little silica desiccant. The transmitters are programmed to comply with ISM-band regulations – no need to run afoul of those rules – while the receiver is just an SDR dongle and a Raspberry Pi running rtl_433. The long-ish video below details design and construction.

The idea behind these vacuum containers would seem to be to pull out humid air and prevent it from coming back in. But as [Scott] quickly learned from his telemetry, following the instructions results in the equivalent atmospheric pressure of only about 2700′ (823 meters) elevation – not exactly a hard vacuum. But as [Scott] points out, it’s enough to get a nice, tight seal, and his numbers show a lowered and constant relative humidity over time.

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Five Dollar RF Controlled Light Sockets

November 22, 2014 by 46 Comments

This is tens of thousands of dollars worth of market research I’m about to spill, so buckle up. I have a spreadsheet filled with hundreds of projects and products that are solutions to ‘home automation’ according to their creators. The only common theme? Relays. Home automation is just Internet connected relays tied to mains. You’re welcome.

[Todd] over at Fabricate.io found an interesting home automation appliance on Amazon; a four-pack of remote control light sockets for $20, or what we would call a microcontroller, an RF receiver, and a relay. These lamp sockets are remote-controlled, but each package is limited to four channels. Terrible if you’re trying to outfit a home, but a wonderful exploration into the world of reverse engineering.

After cracking one of these sockets open, [Todd] found the usual suspects and a tiny little 8-pin DIP EEPROM. This chip stores a few thousand bits, several of which are tied to the remote control. After dumping the contents of the EEPROM from the entire four-pack of light sockets, [Todd] noticed only one specific value changed. Obviously, this was the channel tied to the remote. No CRC or ‘nothin. It doesn’t get easier than this.

With the new-found knowledge of what each lamp socket was looking for, [Todd] set out to clone the transmitter. Tearing this device apart, he found a chip with HS1527 stamped on it. A quick Googling revealed this to be an encoder transmitter, with the datasheet showing an output format of a 20-bit code and four data bits. This was a four-channel transmitter, right? That’s where you put each channel. The 20-bit code was interesting but not surprising; you don’t want one remote being able to turn of every other 4-pack of lamp sockets.

With all the relevant documentation, [Todd] set out to do the obvious thing – an Arduino transmitter. This was simply an Arduino and a transmitter in the right frequency, loaded up with bit of carefully crafted code. [Todd] also figured out how to expand his setup to more than four lamp sockets – by changing the 20-bit code, he could make his Arduino pretend to be more than one transmitter.

With Arduino-controlled lamp sockets, the world is [Todd]’s oyster. He can add Ethernet, WiFi, Bluetooth LE, and whatever trendy web front end he wants to have a perfect home automation setup. It’s actually a pretty impressive build with some great documentation, and is probably the cheapest way to add Arduino/Internet-enabled relays we’ve ever seen.