Adjustable meeting timer with one minute warning

[johnsoax]

Hello,

I'm trying to build a meeting timer for my college fraternity. It's been about 6 years since I took my electronics classes and I was looking for some help.

I would like to have a final product of a box with three lights (Green, Yellow, Red), two buttons (Start, reset), some way to set the time (thumb-wheel switch), and possibly a buzzer (with a switch to kill it).

The way that I would like it to work is as follows:

Say the thumb-wheel is set for 5-min.
When the start button is pressed, the green light lights up.
After 4 minutes, the green light shuts off and the yellow light turns on. (and possibly a very short burst on the buzzer).
When the 5 minutes is up, the red light comes on (and optionally, the buzzer turns on).
The reset button is pushed an then all lights/buzzers are off awaiting next start press.

I was thinking of using two BCD-countdown timer chips and some 74xx logic to pull the 1 min left and 0 readings. Like I said, I havn't done any electronics work for about 6 years (I'm a power systems engineer). Does anyone have a better way? I don't have access to any type of PIC writing equipment, so that is out of the picture. I've thought about just using electromechanical relays, but want a smaller package that can run on batteries. If someone has a really simple circuit, I would appreciate it.

If this has already been discussed, I apoligize, I searched for about 20 minutes before posting this.

 

[aryajur]

Have u decided on the minimum and maximum timing intervals u want to achieve??

 

[johnsoax]

Have u decided on the minimum and maximum timing intervals u want to achieve??

20 minutes to 2 minutes would probably work. We really need 5 minutes, but I want it to be adjustable. I guess that there really is no need for an upper limit if it makes it easier to build.


For the 74xx logic, I would need to grab 111011 for 59 sec, correct?

 

[ljcox]

I would use CMOS rather than TTL, much lower power consumption and much better noise immumity. And the 74C series and the 4000 series can operate at up to 15 Volt.

To do the seconds timing, you would use a Mod 6 counter for the tens and a Decade counter for the units.

The minutes counter would be identical with a carry signal from the seconds Mod 6 to the minutes counter clock.

As for the 1 minute warning, you could use gates to detect when the minutes counter goes to 1.

You will need presettable down counters so that they can be preset to the required time (according to the setting of the thumb wheel switch) when the start button is pressed.

The Mod 6 counter would be a presettable 4 bit binary counter that is preset to 5 each time it reaches zero. There are counters that have an inbuilt carry (or borrow if counting down) signal. This avoids you having to detect zero with gating.

Len

 

[Nigel Goodwin]

Does anyone have a better way? I don't have access to any type of PIC writing equipment, so that is out of the picture.

I really hate to be a boring git - but a PIC (or other micro-controller) would make it so easy - just one chip, your in and out hardware, and that's it :idea:

 

[aryajur]

Well the binary to detect in 74xx logic will depend on the clock u will be using to drive the circuit. If u use binary counters u will have to be satisfied with approximate timings for the minutes because the counters will only provide u increments of 2 times.
A better method giving many timing options and having the capability of 1 minute left functionality would be to use the 4059 programmable divide by n counter. You can have 2 of these and 1 callibrated for always 1 minute less than the oter one. You could feed both of them with a clock from say a 555 timer of a 1 sec period. and then wire the thumbweel switch to wire program the timer appropriately. This would be a simple enough circuit I think, giving u plenty of resolution options and accurate timings as well.

 

[johnsoax]

Does anyone have a better way? I don't have access to any type of PIC writing equipment, so that is out of the picture.

I really hate to be a boring git - but a PIC (or other micro-controller) would make it so easy - just one chip, your in and out hardware, and that's it :idea:

Well, I don't have the resources to use one, which I already stated.

 

[diode]

Does anyone have a better way? I don't have access to any type of PIC writing equipment, so that is out of the picture.

I really hate to be a boring git - but a PIC (or other micro-controller) would make it so easy - just one chip, your in and out hardware, and that's it :idea:

Well, I don't have the resources to use one, which I already stated.

I wouldn't like to insist, but maybe you live under the impression PICs require expensive programmers and development tools.

A simple PIC programmer can be built with one tenth, or less, of the components you are going to use for your timer and assemblers and other software to tranfer the code to the PIC is available for free.

Then, if you tell me that you don't want to invest in the time needed for learning this kind of stuff, that's up to your judgment.

 

[Nigel Goodwin]

Well, I don't have the resources to use one, which I already stated.

There's very little required in the way of resources, all you need is the programmer hardware - which you can buy as a kit for around £10. You already have a computer (presumably, as you are posting here), everything else is free - except for your time learning!.

This is going to cost a lot less than doing it the complicated way.

 

[johnsoax]

There's very little required in the way of resources, all you need is the programmer hardware - which you can buy as a kit for around £10. You already have a computer (presumably, as you are posting here), everything else is free - except for your time learning!.

This is going to cost a lot less than doing it the complicated way.

If you could kindly provide links to a programming kit, and software for a Mac (OSX or OS9), I will try it that way. I don't have a lot of time for this, it has to be built and working by April 2nd. As I have never done this before, please also recommend a good PIC to use. I will have to lean on you guys a lot to get this accomplished.

Thanks in advance.

 

[johnsoax]

I did a little searching and this is what I have found so far

**broken link removed**

Hmmm, all of the programers that it mentions Are expensive.

Warp-13 - $109
Warp-3 can't find
Deck - (**broken link removed**

I've also found **broken link removed**

I really don't think that I have the time to learn this right now, maybe in the future though, this is pretty interesting!

 

[Nigel Goodwin]

If you could kindly provide links to a programming kit, and software for a Mac (OSX or OS9), I will try it that way. I don't have a lot of time for this, it has to be built and working by April 2nd. As I have never done this before, please also recommend a good PIC to use. I will have to lean on you guys a lot to get this accomplished.

As already mentioned by johnsoax, there isn't a lot of Mac PIC stuff about, the lack of ports on a Mac makes them a poor choice for anything like this. Mac's are excellent for many uses, but electronics isn't really one of them :cry:

One possible option (but requiring you writing the Mac programming, or waiting to see if MicroChip ever do!) is the PICKit 1 FLASH USB programmer - all the PC source code is available to download, so you could see what needs to be sent to the programmer.

By far the easiest way is to simply get a PC for PIC programming, you don't a high spec machine, so you should be able to pick one up very cheaply, or even for free! - I threw half a dozen away last year, all of which would have been fine for PIC programming.

As for a suitable PIC, most would be fine, but the 16F628 would be a good choice, it's an EEPROM/FLASH technolgy chip, has an internal oscillator, and gives 16 I/O lines on an 18 pin chip.

 

[johnsoax]

OK, well, I haven't ever bought a PC and I never will, so lets go back to doing this the "hard" way (the PIC way seems harder at the moment ).

Does anyone have any ideas that would work better than what i already mentioned?

 

[ljcox]

See my previous post. If you need more detail, let me know.

Len

 

[johnsoax]

See my previous post. If you need more detail, let me know.

Len

Thanks,

I would like more detail please, if at all possible.

 

[ljcox]

[/quote]

Thanks,

I would like more detail please, if at all possible. [/quote]

Alex,
Here is a starting point for you. It can count down from 99 to 0. If you need more help, let me know

Len

 

[johnsoax]

Alex,
Here is a starting point for you. It can count down from 99 to 0. If you need more help, let me know

Len

For the 4029, would a Texas Instruments CD4029BE fit the bill?
For the 4001, I'm looking at the TI CD4001UBE
For the 4002, I'm looking at the TI CD4002BE
For the 4011, I'm looking at the Fairchild Semiconductor CD4011BCN

For the one minute timer, should I use a 555? or is there a better way?
For a 555, I'm looking at the TI NE555P. I'm seeing what else Digikey has.

For the Thumb switches, I'm actually going to use ITT Industries - RTE1001N13's. Low Profile Rotary Dip Switches (with Extended Shaft)

So far that is as follows

#  QTY                                                    $ (each) 
1   6 296-2046-5-ND IC PRESET UP/DWN COUNTER 16-DIP    (0.46) $2.76 
2   2 296-14077-5-ND IC QUAD 2-IN NOR GATE 14-DIP      (0.46) $0.92 
3   2 296-2029-5-ND IC DUAL 4-IN NOR GATE 14-DIP       (0.46) $0.92 
4   2 CD4011BCN-ND IC GATE NAND BUFF QD 2INP 14-DIP    (0.41) $0.82 
5   2 401-1032-5-ND SWITCH ROTARY 10POS BCD SHAFT      (2.91) $5.82

All for a grand total of $12 (+ S/H and Tax)

I'm buying extra counters because I'm thinking about doing seconds also and then putting in an LCD.

You've been a great help, thanks. (If you see that I am using the wrong chip, please let me know!!)

 

[johnsoax]

I'm thinking of using 4 TI CD4511B CMOS BCD-to-7-Segment Latch Decoder Drivers to display the 4 digits (00:00) of the countdown.

 

[ljcox]

Alex,
Yes those ICs are suitable. BUT, before you purchase, you should do the full design as it is usually possible to optimise once you have the full picture. For example, the half 4002 gating could be implemented using two halves of a 4001 and a third of a 3 input NAND IC (if this proves to be more economic once the overall parts count is considered).

"For the one minute timer, should I use a 555? or is there a better way?"

Yes there is. A 555 will not be very accurate. It would be better to use a crystal oscillator and binary dividers. Besides, you said that you may include a seconds counter. If so, the minutes counter will be driven by the "carry out" of the seconds counter. The seconds counter will need a seconds clock which could be a 555 or, if you want better accuracy, a crystal oscillator as above.

"For the Thumb switches, I'm actually going to use ITT Industries - RTE1001N13's. Low Profile Rotary Dip Switches (with Extended Shaft) "

Does this switch convert from decimal to BCD?

Also, if you include a seconds counter, it will need a Modulo 6 counter. Do you intend to use Thumb Wheels to set the seconds also?

You will also need to include some control logic - to do the sequencing, light the LEDs, etc.

So I suggest you draw the full circuit and post it so I and others can make suggestions before buying parts.

Len

 

[johnsoax]

BUT, before you purchase, you should do the full design as it is usually possible to optimise once you have the full picture. For example, the half 4002 gating could be implemented using two halves of a 4001 and a third of a 3 input NAND IC (if this proves to be more economic once the overall parts count is considered).

Thanks so much. Now that I have the general idea, I can run with it. I was just looking at prices. I will draw this up tomorrow and try to get it up here!

"For the one minute timer, should I use a 555? or is there a better way?"

Yes there is. A 555 will not be very accurate. It would be better to use a crystal oscillator and binary dividers. Besides, you said that you may include a seconds counter. If so, the minutes counter will be driven by the "carry out" of the seconds counter. The seconds counter will need a seconds clock which could be a 555 or, if you want better accuracy, a crystal oscillator as above.

I quess that I will use a crystal and a divider. I will have to reseach this.

"For the Thumb switches, I'm actually going to use ITT Industries - RTE1001N13's. Low Profile Rotary Dip Switches (with Extended Shaft) "

Does this switch convert from decimal to BCD?

Yes

Also, if you include a seconds counter, it will need a Modulo 6 counter. Do you intend to use Thumb Wheels to set the seconds also?

What is a Modulo 6? I was thinking about just hard wiring the seconds so that you could just set the minutes, but it wouldn't be much harder to just have a similar set of switches for the seconds.

You will also need to include some control logic - to do the sequencing, light the LEDs, etc.

The outside logic I havn't thought of yet, but will work on.

So I suggest you draw the full circuit and post it so I and others can make suggestions before buying parts.
Len

I will start drawing it tomorrow, unfortunetly I am busy tonight. I will have to draw it into powerpoint or paint (maybe I will download Pspice and see if I can get that running )