Member #115584

Member Since: January 17, 2010

Country: United States

  • Neat demonstration. Explanation should be “commutative” rather than “communiative”.

  • Since we left the competition way back there, Sparkfun has nothing to worry about now.

  • In the video, it was stated that the IR was not visible to “Greg’s really fancy camera” until a pair of polarizing sunglasses were introduced. It was also stated that the cell phone camera worked because it contains a polarizing filter. I wish this had been explained. I suspect that something other than polarization is going on here.

  • Why does the polarizing filter make the IR light visible to the camera?

  • Yes. Define the oscillator as P181 in the UCF file and as an input in your code. Things should work.

  • The description includes the words “exponential decay” and the equation is exponential decay, but the voltage is growing to an asymptotic value, not decaying to zero. The equation for the red line should be V(t)=V_in[1-exp{-t/RC}]. The equation Vt)=V(0)exp{-t/RC} will work for the second half of the source signal cycle. Very nice presentation.

  • This thing is not very accurate, as others have noted. However, the one I have is very stable. Using this device to produce an accurate time requires a little software to remove the drift. If you do this, it’s better to let the clock drift and compute a correction than to occasionally reset the clock. Two of the 56 ram bytes can be used to store a reference time. I have a clock that is working well with this approach.

  • I had inconsistent results with smaller caps and ended up using 3.3 uF. That’s been working fine for me.

    If you want to load with the reset button, it works to hold the button down, upload the code, and then release the button the instant that you see the TX LED on the FTDI board light up. That also seems to work consistently, but the capacitor is easier.

  • Should that be 2.5x100mm?

  • With this board, you are down to the basics. Nothing but the gate array, voltage regulators, the prom, RS-232 level converters, and an oscillator. Digilent boards are good if you want switches, buttons, LEDs, and 7-segment display. OpalKelly boards are more focused on the gate array and bring out more pins without much clutter. GadgetFactory Papilio boards look like good starters (I don’t have one). This Sparkfun board brings out EVERY pin with no clutter at all. It provides control over the individual bank VCCO voltages. Many boards won’t let you experiment with LVDS at 2.5V, for example. This one does.
    The prom is not on the JTAG chain, which seemed inconvient to me at first, but it has advantages. It makes the prom more easily accessible by the FPGA and/or an external device. The prom is 16 Mb, but the bit file uses only a little more than 2 Mb. All that additional prom space is available for any purpose.
    If Sparkfun is going to continue this product, it would be nice to post a link to an example UCF file. It’s not hard to generate the file from the schematic, but it would save a step and lower the barrier for some users.

No public wish lists :(