I seem to be having trouble designing a 30 minute countdown timer. Building a timer to count up to 30 minutes, however, is no trouble. Articles I have read is very vague in describing the design process. This clock is using minutes and seconds. Can anyone help me?

Regards,
Cableguy

 

Originally posted by cableguy@May 26 2006, 05:16 PM
I seem to be having trouble designing a 30 minute countdown timer.  Building a timer to count up to 30 minutes, however, is no trouble.  Articles I have read is very vague in describing the design process.  This clock is using minutes and seconds.  Can anyone help me?

Regards,
Cableguy

[post=17344]Quoted post[/post]​

I can think of at least four different ways to do it.

1. Binary down counter with BCD Conversion and display.
2. BCD Down Counter with direct display.
3. FPGA using VHDL or Verilog.
4. Microcontroller with display.

Can you tell me what I have to work with?

 

Originally posted by Papabravo@May 26 2006, 11:12 PM
I can think of at least four different ways to do it.

1. Binary down counter with BCD Conversion and display.
2. BCD Down Counter with direct display.
3. FPGA using VHDL or Verilog.
4. Microcontroller with display.

Can you tell me what I have to work with?

[post=17350]Quoted post[/post]​

I wish to use jk flip-flops if possible.

 

From the list Papabravo has provided I would personally advise using a Microcontroller with a couple of 7-segment displays. PIC microcontrollers are highly-suitable to develop counterdown timers using the integrated timer module on-chip. Most of the PICs employ at least an 8-bit timer/counter module and in many cases have a 16-bit version. You could get your hands dirty doing this in assembly language or could use a high-level language such as C.

If you choose to look at using a PIC microcontroller you can develop your countdown timer using the MPLAB software, available from Microchip.

As for your idea of using JK flip-flops, is there any particular reason you wish to use such components?

Dave

 

Hi,

Gotta agree with Dave. The sheer number of j-k flip flops needed for the function is huge.

Look up a parallel-load up/down counter datasheet (in whatever logic family you are planning to use), and life gets lots easier.

 

Originally posted by beenthere@May 28 2006, 11:36 AM
Hi,

Gotta agree with Dave. The sheer number of j-k flip flops needed for the function is huge.

Look up a parallel-load up/down counter datasheet (in whatever logic family you are planning to use), and life gets lots easier.

[post=17380]Quoted post[/post]​

In stead of using the microcontroller could I use 74HC192 (Presettable Synchronous Up/Down BCD Counter) to do a 30-minute count down?

Thanks,
Cableguy

 

Originally posted by cableguy@May 28 2006, 05:37 PM
In stead of using the microcontroller could I use 74HC192 (Presettable Synchronous Up/Down BCD Counter) to do a 30-minute count down?

Thanks,
Cableguy

[post=17389]Quoted post[/post]​

That should work just fine.
Good Luck

 

I noticed that this timer has to count seconds too, which is a bit more complicated than just a counter. (I'm not sure about this, but I was thinking it might need two counters. And a little logic to load the seconds counter with 59 after it hits 0.)

Edited to add: the 74HC192 is only one digit anyway. So... that's not a problem really. Just the high seconds digit needs to go to 5 after 0.