• R/2R Digital to Analog Converter

    R/2R Digital to Analog Converter

    The first thing I wanted to do with the new oscilloscope was to test the X-Y-Mode. Not with some lame Lissajous-figures but with arbitrarily adjustable positions. And the easiest way to to so, was to take an ATMega32 and two DAC’s.

    I had two parallel-input DAC’s lying around, but i did not want to make a layout or to wire so many pins.
    The next best alternative was to build two R/2R-resistor ladders. I found a large amount of 620kΩ resistors (can’t remember why I bought them. They seem to have been there for years.) and some perfboard.

    I wired the resistor networks directly to Port A and B of the AVR, so I could directly assign 8-bit numbers to the port register. I wrote a simple program where an interrupt updates the ports at ca. 30Hz and displays some bouncing dots.

    Tags: , , , , ,

  • When the timebase knob on my old Hameg HM-312 fell off, i decided that it was time for a new oscilloscope. After all, the old one has endured my using for almost 10 years now. Actually the old one had everything I needed.

    Hameg HM-1005 Oscilloscope

    Hameg HM-1005 Oscilloscope

    I considered buying a digital storage oscilloscope, but other than the measuring functions for frequency and duty-cycle, I would scarcely need any of the additional features this would offer over an analog model. Additionally the price for an analog one is only about a third.

    eBay offered a wide variety of analog oscilloscopes, mostly from Hameg. After a few days of searching and comparing, I found a relatively cheap HM-1005, which has 3 channels, 2 separated timebases and adjustable trigger-offset and bought it.

    The package arrived only 4 days later, but unfortuneately I found one edge of the case partly broken and the intensity knob totally destroyed. Some moron at the post office must have dropped the package. After further inspection it appeared that not only the knob was destroyed but also the axis which connects the knob to the potentiometer was split in half.

    Not keen on a fight with the post over who is to blame for the damage, I opened the case and tried to repair the broken axis. Some glue fixed the problem and the knob was replaced by knurled screw.

    The old HM-312 is still in use. I even fixed the knob. Was quite easy, but i needed an excuse to buy a new one…

    Tags: , ,