Posts Tagged “hardware”

  • Experiments with a 74HC14 Schmitt-Trigger IC

    A recent PetitFoo talk at the Chaospott on how to debounce keys with a Schmitt trigger prompted me to play with a 74HC14 IC I had lying around.

    A Schmitt-trigger converts an analog voltage to a digital logic level. It has two voltage thresholds, and the interesting thing happens between the two:

  • Below the lower threshold the input is considered logically low, so the inverter outputs a logic high.
  • Above the upper threshold the input is considered logically high, so the inverter outputs a logic low.
  • Between the two thresholds the Schmitt-trigger keeps the input state, so the output doesn't change.
  • That last part of the behavior is called hysteresis. It helps to avoid uncontrolled switching due to noise on the input, especially when the input is changing slowly compared to the switching speed of a logic IC.

    Basic Behavior

    Here is an oscilloscope screenshot of the basic behavior of one inverter of the 74HC14, using a triangle wave from the function generator as the input: Oscilloscope screen showing 74HC14 schmitt-trigger behavior More ...

  • Testing the delay of LPC804 PLU LUTs

    The LPC804 is a new low-end microcontroller from NXP in the LPC8xx range. The LPC804 is interesting, because so far it is the only LPC microcontroller which contains a Programmable Logic Unit (PLU), a miniature FPGA with 26 5-input lookup tables and 4 bits of state. Unfortunately NXP doesn't publish the timing parameters of this circuitry. You are supposed to use NXPs proprietary PLU configuration tool, which is available only for Microsoft Windows.

    Here is a quick measurement of the speed of the LUTs in the PLU: Oscilloscope screen with delay measuments More ...

  • J-Link Internals

    J-Link circuit board
    In case you are curious, here is a picture of my Atmel SAM-ICE aka Segger J-Link board. More ...

  • Some Pictures of NXT Production Hardware

    Here are some pictures of the hardware of a production NXT.

    View of the top side of the NXT mainboard This is a view of the top of the motherboard. According to the schematics released by LEGO the part missing in the upper right was a battery current sensor on AD5. The black smudge at the square speaker connector covered an additional part in the speaker cable, a 10 Ohm resistor which is not in the schematics. I unsoldered it together with the speaker cable to get the LCD daughter board out of the way for photographing the motherboard. More ...