In this lab, we implemented an 8-bit up/down counter by concatanating two SN4191 chips (4-bit counters).  An LMF311 comparator was used to compare an analog input to 2.5 V.  If the input was below 2.5, the counter would count down and vica versa.  if the input was exactly 2.5 then the counter would oscillate (count up 1, then down 1).

Although our circuit worked well counting up and down, we could only get it to oscillate a few times, when we didn't have the camera :(

click on the image to see a video of the counter.