# Digital Electronics Homework Help

Discussion in 'Homework Help' started by IcyIcy, Sep 16, 2014.

1. ### IcyIcy Thread Starter Member

Nov 17, 2012
32
0
I need help in creating a weighted timing controller. The problem is as shown below.

Creating a Weighted Timing Controller:

A simple microwave oven has two cooking modes: a "Slow cooking" mode that operates on low power and a "Fast cooking" mode that operates on high power. Cooking time for these cycles depends on the weight of items being cooked and is determined as follows.

Fast cooking cycle: 2*Weight seconds
Slow cooking cycle: 3*Weight seconds

The system will not be functioned if the cooking cycle is more than 15. The weight is indicated by a 4-bit DIP switch. A 1-bit DIP switch is used to indicate the cooking mode (fast or slow). A push button is used as START button for starting the cooking process. A seven segment display and a LED are used to indicate the count in decimal format and only odd number count is showed during the cooking process. For example, if the count is 15, the LED is asserted and seven segment shows '5'. If the count is 9, only the seven segment display shows '9'.

Implement the 4 bit weight DIP switch, 1 bit DIP switch for mode selection and cycle calculation.

I try doing this using 4 JK flip flop and have a 4 input NAND gate (4 bit DIP switch) tied to the clear. But, I am not sure if this is the correct way and I do not know how to implement the 1-bit DIP switch for mode selection and cycle calculation (how do I make it 2*weight or 3*weight second)?

Thank you for the help you render and if possible, please guide me on how to begin.

2. ### tshuck Well-Known Member

Oct 18, 2012
3,527
675
First thing to do is to capture the operation of the device e.g.:
Fast Mode:
• Cook time=(2*Weight) seconds
• Display cook time
• ?
Slow Mode:
• ?

This way, you can look at the functions of the device and attempt to group common functions into a single implementation.

Next identify inputs and outputs of the device and how they cause various actions to be performed.

Write a state diagram and a state transition table (showing inputs and outputs).

Are you familiar with state machines?

What are your limitations on implementations?

3. ### IcyIcy Thread Starter Member

Nov 17, 2012
32
0
Currently, I could use any ICs for the implementation. Would JK flip flop works for this?

4. ### tshuck Well-Known Member

Oct 18, 2012
3,527
675
JK , D, T, you could use whatever flip flops you'd like, though some are better suited for a given purpose...

5. ### IcyIcy Thread Starter Member

Nov 17, 2012
32
0
But, how do I implement the 1 bit DIP switch (Fast/Slow cooking mode) and the 4 bit DIP switch (Weight)? Is it the 1 bit DIP switch attached to the clock?

6. ### IcyIcy Thread Starter Member

Nov 17, 2012
32
0
Is it possible if you could show me the way? Cause I am really clueless.

7. ### tshuck Well-Known Member

Oct 18, 2012
3,527
675
The slow/fast mode is an input to the system, it determines which states in the state machine are used in a given cycle.

The weight is another input to the system (it just happens to be 4 bits).

Again, have you used state machines before? Do you know what a state transition diagram is? What about a state table?

Have you looked at the eBook section on state machines?

8. ### IcyIcy Thread Starter Member

Nov 17, 2012
32
0
I am able to find solve the 4 bit DIP switch and 1 bit DIP switch, however, I am required to only produce odd number on the seven segment display. May I know which IC should I use so to produce only the odd counts?

9. ### tshuck Well-Known Member

Oct 18, 2012
3,527
675
I'm not sure what use a chip that only displays odd numbers would have in a production run...

...you could always try to work the logic out yourself...

You have the count already, presuming you've worked out the first part. Certainly you can figure out how to determine if the binary count is odd, right?