6.5 minute speech timer, Please help

[Sleeve]

Hello everyone, I am a complete newbie to this sort of thing, so please bare with me.
I am in a spokesman's club and have been given the project of building a coloured light timing device using red, yellow, and green leds. The lights can all be lit at the same time with each one going off at a set time, or each light can be lit up in succession like a traffic light. The green light would stay on for approx. 3 min, then the yellow for 1.5 min then the red for 1 min. etc. I would prefer the latter method. I have done some research, and have come to the conclusion that I will need 1 or more 555 timers, resistors & capacitors of various sizes. What I am not to certain of however, is if I will need a 4017 counter or not, and what types of resistors/capacitors I will need to achieve the 6.5 minutes I need. Any and all help would be greatly appreciated. Thanks

 

[Harald Kapp]

If all LEDs are allowed to be on at the same tiem, you can make a simple circuit using 3*555 timers in a monoflop configuration (link). Connect the LEDs via a series resistor from the output of the monoflop to ground (0V). See the Section on LEDs in this forum for details about the series resistor.
Set the first monoflop to 3 minutes
Set the second monoflop to 4.5 minutes
Set the third monoflop to 5.5 minutes

Connect the trigger pushbutton to all three monoflops. When pressing the pushbutton all Monoflops will be started and all LEDs are on. After 3 minutes the LED (green) connected to the first monoflop will turn off. After an additikonal 1.5 minues the LED connected to the second monoflop (yellow) will turn off. And so on.

Alternatively, if you don't want all LEDs on simultaneously you can modify the circuit as follows:
Build a first monoflop using the pushbutton for trigger. Connect the red LED to this monoflop and set the time to 3 minutes.
Build a second monoflop using the edge-trigger circuit (same link, a bit further down) and connect this trigger to the output of the first monoflop. Connect the yellow LED to the output of the second monoflop and set the time to 1.5 minutes. Make a third monoflop (red LED, 2minutes!) which is edge triggered by the second monoflop.
Optionally build a fourth monoflop edge triggered by the third monoflop. connect a DC-buzzer to the output of this monoflop and set the time to e.g. 5 seconds. This option will sound a buzzer tone after 6.5minutes.

Regards,
Harald
P.S.: You could use a small microcontroler to achieve all this with little effort in software. However, you would have to be able to write the program and to program the microcontroller.

 

[Sleeve]

Thanks Harold, I will give these two methods a try when I receive the components. Will post how I'm getting on with the project, as and when either the project is complete, or need help. Which ever comes first.

 

[bddpaux]

Can you help out a 'yank like me.....? "Spokesman's Club....?"

As in, public speaking??

 

[BobK]

Or you could use a microcontroller, 3 LEDs 3 resistors and that's it. And you could then have multiple programs for different length timings etc.

Bob

 

[(*steve*)]

Yeah, 555's with suck long delays are likely to be less than perfect.

I'd go with a microcontroller or a faster oscillator that is divided down to a very low frequency. Even with the latter and a 4017, if you want 30 second resolution the maximum time will be 5 minutes.

 

[CocaCola]

I can program up a small micro to do this for a small fee if you are up to actually building the circuit from that point... If it's just single LEDs as Bob said, just hook up the LEDs and limiting resistors but if you want multiple LEDs or what not use a Darlingon IC or transistors/resistors, either way would work... I assume you will also want a button to start, stop and reset the device so that would be needed as well...

 

[KrisBlueNZ]

As Steve says, 555s are not very accurate, and I guess some accuracy will be needed in this application.

A microcontroller would be the obvious way to go here, because it's accurate, compact, and versatile. Of course the jump into microcontroller development is much bigger than the jump into general electronic design and construction, so I'm glad that CocaCola has offered to program a device for you. You should have a good think about what features and flexibilities you will or might want, since these are best designed-in at the start. You can build in a DIP switch that can be read by the software, to control timings and behaviour options.

Another option was hinted at by Steve. That is to use a crystal-derived clock frequency and a series of counter/divider ICs, such as the CD4020, CD4040, CD4060 and CD4017 from the 4000-series CMOS device family, to translate these into accurately timed signals with the characteristics you need.

Suitable clock sources would be the Dallas/Maxim DS32KHZ device (http://www.digikey.com/product-detail/en/DS32KHZ/DIP/DS32KHZ/DIP-ND/420263) or various crystal oscillators with higher frequencies, or a 32768 Hz "watch crystal" (cheap) used with a CD4060 (built-in oscillator gates).

You would need several divider ICs to divide the frequency down to a usable frequency - probably you would divide it down to 1 Hz (one pulse per second) and from there, divide it by 30 to get your half-minute pulse, and from then, use a 4017 to produce a signal at each multiple of 30 seconds.

I would be happy to help with schematic designs and advice if you decide to go down that road.

Good luck!