Wednesday, June 30, 2021

Economical 12 Vdc power supply

Purchased an Xbox 360 power supply at the thrift shop for a few dollars. It has a relatively powerful 14.2A 12V output. Found out there are 3 versions (16.5A, 14.2A, and 12A) and others have converted them to power supply use.

Cut the factory dc plug and connect the red and blue wires together to switch the supply on when it's pluged into ac power. You can wire them together permanently or even switch it electronically and have a remotely controlable dc power supply.  

The voltage is a bit low @ 12.2V, but is acceptable and does not drop too much under load. As far as noise it is surely not in the same league as a proper (much more expensive) power supply. However, I have tested it briefly on the HF bands and was still receiving quite a few signals. It's definitely superior to other cheap 12V transformers and chargers I have tested. Should work great for VHF+ use but not ideal for 24/7/365 application, as it wasn't designed with extended continous use in mind and there is a variable speed internal fan which would probably fail after some time. Still, considering the cost, it makes a decent portable or spare/beater power supply

Xbox 360 power supply with 30A Anderson connector installed.  Noise on HF could be further improved by adding more impedence in addition to the single choke that is on the dc output cable from the factory.

Tuesday, June 29, 2021

APRS Weather Station

Added weather station (WX) temperature, % relative humidity, and barometric pressure data to APRS igate. As with most APRS fixed stations KL3RR-2 periodically sent a packet out containing a position and static "comment" which has now been replaced with (more useful) weather telemetry.

Reading temp + RH over RF (433 MHz) from an Acurite wireless remote sensor using an RTL-SDR and rtl_433.  Many other brands and models of wireless weather stations are supported. Barometric measurements are from a Bosch BMP 280 communicating with the Raspi through I2C bus.  

The pressure measurement is corrected to sea level barometric pressure and all parameters are fed into APRS client XASTIR through a "networked WX" interface using a combination of shell + python scripts and the network utility nmap.  (Inspired by wxserver.sh)

 

KL3RR-2 Raspberry Pi igate + WX

 

Bosch BMP280 absolute pressure sensor on Adafruit board in "custom" enclosure. Accurate to ±1 hPa / mbar. 

 

KL3RR-2 sending a WX packet (XASTIR on Raspberry Pi OS).

A week of weather data as presented by aprs.fi.  KL3RR-2 sends out a WX packet every 30 minutes.    

This weather data can also be provided to the Citizen Weather Observer Program directly through APRS-IS.  Submitting WX data to this program provides useful quality analysis which can help detect problems and improve the accuracy of the station.