Design with D-Type Latch

  • Thread starter Thread starter kal22
  • Start date Start date
  • Tags Tags
    Design
AI Thread Summary
To control 8 microphones using an octal D-type transparent latch on a first-come-first-serve basis, the latches should be made opaque when one mic is activated to prevent others from interfering. The circuit design requires additional logic gates, primarily AND and OR gates, to manage the latch enable signals effectively. The discussion emphasizes that synchronization may not be necessary, as the likelihood of simultaneous button presses is low. A proposed solution involves using logic to ensure that latches remain opaque once a mic is keyed and only return to transparent when all buttons are released. The focus remains on using latches and simple logic rather than complex synchronizers.
kal22
Messages
6
Reaction score
0
How would I use an octal d-type transparent latch along with other logic to control 8 mics on a first-come-first-serve basis? There are 8 input mics and 1 output mic. Only 1 input mic can be used at a time. If a 2nd mic is keyed, I do not want it to take away control from the 1st mic in use.
 
Engineering news on Phys.org
Is this a homework assignment?

Well, the latches only transmit their inputs when they're transparent. So, when one mic is keyed, you make the latches opaque...

- Warren
 
It's a small part of a project.

I need to trip the relay of the 1st mic that's keyed and make sure that the other ones don't activate as long as 1st still has control of the output.

I'm not sure how to get started. Any ideas?
 
Didn't I just give you the answer?

- Warren
 
Well, according to the function table for the 74HCT573 octal d-type transparent latch, whenever the latch enable input goes high, the Q outputs will follow the D inputs.

For this project, a D input will be high if that particular mic has been keyed. More than one mic can be keyed at a time, thus, more than 1 of the 8 Q outputs can be high. A high output signal will trip a relay that will activate a mic. So, more than one mic can activate at a time - which is what I don't want. I need to add logic gates somewhere.

I don't if what you've answered is what I was looking for. Maybe it is, but I just need more clarity. Thank you for your help.
 
Do you know what a synchronizer circuit is, and what it is used for? You need to synchronize your asynchronous switch inputs into a clocked circuit, and have the clocked circuit arbitrate the relay enable signals.

Since this is so close to homework/coursework, you need to show us your work and progress before we can give you much more in the way of hints.
 
Actually, berkeman, I don't believe this needs to be a synchronous circuit at all. All you need are some AND and OR gates (mostly ORs).

- Warren
 
chroot said:
Actually, berkeman, I don't believe this needs to be a synchronous circuit at all. All you need are some AND and OR gates (mostly ORs).

- Warren

But what about ties?
 
berkeman said:
But what about ties?

In practice, ties will never happen. We're talking about people pushing buttons, aren't we?

The probability of two people pressing two buttons within a nanosecond or two of each other is about the same probability of a three-stage synchronizer circuit becoming metastable. Fuhgetaboutit.

- Warren
 
  • #10
chroot said:
The probability of two people pressing two buttons within a nanosecond or two of each other is about the same probability of a three-stage synchronizer circuit becoming metastable. Fuhgetaboutit.

Valid point -- I guess I just like to synchronize everything. But, ask yourself, WWJD? (What Would Jeopardy Do?) I'll bet that their buttons go through synchronizers, and ties are resolved with a PR number generator... Gotta go check that out...
 
  • #11
Well, unbounced switches could lead to some interesting ties, especially if the switches bounce for anything more than a millisecond.

I firmly agree that the better solution (the "Jeopardy solution") would be to synchronize the inputs and use something like a priority encoder. But, the OP is instructed to use latches, and that smells like asynchronous logic to me.

- Warren
 
  • #12
yes, each mic has a push-to-talk button.

so far, what I've thought of is connecting an XOR gate to the latch enable input. i'd have the same 8 mic inputs going into the XOR gate as the ones going into the D inputs of the latch. i'd also have some kind of delay before the 8 D inputs, so that the latch enable input becomes high before more than 1 of the D inputs will become high.
 
  • #13
No need for any delays, nor any XORs. You just need some logic to "look at" the inputs on the left, and the output on the right.

The logic on the right produces a signal to turn the latches opaque as soon as a single button has been pressed and has propagated through the latches.

The logic on the left produces a signal to turn the latches transparent again as soon as all the buttons have been released.

The latches should be opaque only when the left side and right side both agree they should be opaque. This implies a single AND gate.

- Warren
 
Back
Top