A to D Converter Latch Circuit Help

[SteBenno]

Good afternoon everyone,

Just getting to grips with multisim as part of my college course but seem to have hit a bit of a brick wall

Its a modification of the built in ADC example circuit within Multisim

What I am trying to do with the attached circuit is to have the LED Latch ON when the number is 7F and remain on if the number is increased

Then, as the number decreses to 7D, I need it to Latch OFF and remain off as the number decreases

I have tried many means and methods, the best of which I have been able to get is for it to latch on at 7F but on the way down, 7E turns it off and for some reason, 6F turns the light back on

As the circuit stands at the minute, its a little messed up and turns off at 80, I cant seem to figure it out and its driving me insane

Any help/advice would be greatly appriciated, thank you

Steven

[Miguel_V]

Hey,

Just quickly looking at your file, you seem to have a nor latch (the subcircuit) in a restricted state at some point (by routing the Y5 to the S input in your latch). I've never made this circuit nor have a great amount of experince with latches, but from my experience, this creates race conditions, and breaks the latch table (basically making Q='Q, which makes no sense). Since it's not a flipflop, a JK latch won't toggle the output the way a filp flop will, since there is no clock source after a certain point. Maybe this is not the problem and this was intentional, just my 2 cents.

I would also instead of using modeled components, just use a virtual ones to verify your circuit works well. You'll find all the virtual components under the Misc Digital family.

Good luck,

[Josh_E]

Hi SteBenno,

I took a look at your circuit.

In my opinion, what you need is some combinatorial (no memory needed) logic that takes in the 8 channels and then decides whether to output True or False dependent on the state of these lines.

I imagine this wouldn't be too hard to implement but you'd need to do some digital logic circuit design (boolean algebra or Karnaugh mapping) to figure out what logic element's you'd need.

Alternatively, you could use a Digital to Analogue Converter (DAC) to convert the 8-bit value into an analogue voltage (between 0V and 5V). You could then use a comparator circuit to compare the voltage to reference voltages (7F would translate into an analogue voltage of 2.5V if the DAC was 5V based) and decide whether the output should be True or False.

I hope this is helpful, good luck!