A Microcontroller Operated SWR Meter
1 Project description
This project is related to the SVXLink project. Since I intend to use T7F transceivers for this project, it is highly interesting to detect troublesome antenna and SWR conditions and to be able to shut off the transmitter. The only way to do that is to read out the SWR digitally. And this can be done using an Analog Digital Converter, either directly on a microcontroller board or over an I2C BUS.
BTW, I want to measure some more values:
- PA temperature
- Transmitter power consumption / input current
- Total system input current
And I want to switch some things, too:
- Be able to switch the transceiver OFF
But very basically this project can also be seen in an isolated perspective: I want to learn how to use a microcontroller and set up a project that's useful for other OMs as well. Notably interesting will be to use the Sparkfun Low Current readout boards and feed this voltage into the ADC that's contained on the Arduino board. so that I possibly don't even need the I2C BUS for this isolated scenario.
The LCD display is a ANAG Vision AV2020YFBF-SJ
2 Other People's work
- http://www.dk0fr.de/aktuell/DARC/SWR-Powermeter.pdf A similar project but on a different uC basis
- http://www.dj4uf.de/projekt/swr/swr.htm - cool idea for a simple directional coupler. I see that a Aircell cable is perfectly suited for this job.
- http://accrochages.drone.ws/en/node/125 - a voltage meter project based on the Arduino
- http://www.foxdelta.com/products/swr-hf.htm <- There you can buy pre-assembled kits, but that's not what I want.
- http://www.pr8-online.de/index.php?option=com_content&task=view&id=46&Itemid=33&lang=de Excellent introduction into LCD usage with the LCD screen I am using
- http://home.snafu.de/graff/swr.html A similar project with several couplers
3 Shops where to buy the components
- http://www.watterott.com (Germany)
- http://www.sparkfun.com/commerce/categories.php (USA)
- http://store.gravitech.us/ (USA)
- http://www.horter.de/ (Germany)
4 Project Plan
- Purchase stuff
- Get familiar with the Arduino board. See how to read out values and to control actuators.
- Build a directional coupler. Role model: http://www.dj4uf.de/projekt/swr/swr.htm
- Make sure the readouts of the forward voltages are within a reasonable range. identify peak voltages.
- Then take the BeagleBoard and be successful measuring voltages through a Analog Digital Converter (ADC).
- Then connect the coupler to the ADC and see if it's possible to measure the voltages.
- Then connect an LCD display to an Arduino board.
- Then successfully control the LCD display and devise a reasonable display readout
- Then read the I2C bus from the Arduino board
- Then calculate the SWR based on the readings from the I2C bus and send them to the LCD display
- Finally build a nice case
- Write an article and post it in some fancy electronics magazine :-)
5.1 Purchase Stuff
- 2009-09-04 The BeagleBoard has an I2C header in the expansion port. So it is just a wonderful idea to use it and read out some things. The only problem: It's operated with 1,8V. So I need a bidirectional voltage translator.
- I found one across the Atlantic at Ebay: Gravitech has such a thing for a decent price: http://gravitech.us/MicroResearch/I2C/I2C-TRN/I2C-TRN-Manual.pdf
- Another option would be to built it by myself using the PCA9306: http://focus.ti.com/docs/prod/folders/print/pca9306.html
- 2009-09-05 I decided to get the one from Gravitech.
- 2009-09-10 My ADC arrived. I'm still waiting to receive the voltage translator. And I have bought some books on Arduino programming. Still need to buy the Arduino board and an LCD display.
- ToDo: Go shopping
- 2x C 1nF
- 2x R 100 Ohm
- 2x diodes Schottkydiode
- 20cm Aircom cable. It has those practical canals in the dielectricum through which you can stick the sensor wires. (nope, I got a directional coupler from Ebay)
- The Arduino board and the LCD display
There are some guides on how to connect LCD dislays and Arduinos:
5.3 The Directional Coupler
Hardware is ready. I managed to find a wonderful Directional Coupler on Ebay. This coupler produces two RF AC currents. One for forward, the other for reflected power. I am leading these currents through diodes into an ACS712 Low Current Sensor, which produces a voltage between 0V and 5V. This voltage again can be measured by the ADC in the Arduino.
6 What's next?
- Programming the Arduino and master the control of the Transceiver.
- Come back and see in a few weeks / months...