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Count Down Timer

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RetiredHAL

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Hi, I would like some ideas as to how to go about this project. If possible I would like to not use a PIC as I am not experienced in PIC.
This timer would be used for boiling eggs, timing scrabble moves, and generally as a 12 hour countdown timer, but capable to accurately count down in 10 sec intervals. I can do the timer generation, count down part and display part , but I am having problems setting the time in an easy manner. I would like to mount the components behind perspex to show off the workings. Yes I know I can buy one for $20.00 but that is not the point. I would like to make this a piece of art to show my grandchildren what ICS are capable of. In another 10 years they will not know what CMOS is.
I would like to use Decadic Rotary switches to set 1H.MM.S0. I would like to use Cmos for power considerations. There is a 40147 IC that would readily translate the switch setting to BCD, but they are hard to source. Can you think of other methods to translate a Decadic switch position to BCD, other than a discrete diode matrix? I would like to use Rotary switches for the "Retro" effect and also for ease of use.
I have been all over this forum and have seen some beautiful clocks but not countdown timers.

Cheers RetiredHal
 
RetiredHAL,

Attached is a down counter circuit using ICM7250 I use on a spot welder. This uses a 60Hz clock and gives a BCD down count. Their ICM7220 gives a modulo 60, and cascaded, with a 1 second clock, would work for you timer...I think.

https://www.electro-tech-online.com/custompdfs/2008/01/ICM7240-ICM7260.pdf

Ken

OOps...it's an up-counter...but still might work for you.
 

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Countdown timer

Hi retiredHAL,

if it is just the switch you won't have to worry. There are BCD coded switches showing displaying decimal values. All you have to do is to connect the switch properly.

Since you intend to use CMOS-ICs I don't have a ready circuit at hand. I you decide to use Low power Schottky devices I can send you a two digit count down timer circuit using 74LS192. It counts straight foreward just minutes or seconds. (without a carry at a full minute).

You don't want to boil an egg for 12 hours, do you?

Reminds me to my wife. She boiled an egg for two hours and wondered why it wasn't soft. She argued: "Something must have been wrong with the egg." :D

Regards

Hans
 
on1aag said:
You're gonna get extra long hours ! :D

on1aag.

OK...I'll bite..... :confused:

Ken
 
Thank you Boncuk for your suggestion of BCD switches, I did not realise that they came in anything else than thumbwheels or screwdriver set versions. Unfortunately there is very little choice and they are quite expensive.
Thank you KMoffett for that link to the 7217. I dont think it will do as I really want a six digit display and a quick look at the Datasheet makes me think that it will only serve a 4 digit display timer .Also I could not find the 7217 Ic in Farnell,Jaycar,RSonline or Altronic catalogues
My biggest problem is not so much getting the bits together, but not having to source from too many suppliers, and basically I want to restrict my sourcing to Australia to cut down on postage and handling cost.

Cheers RH
 
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RetiredHAL said:
Thank you Boncuk for your suggestion of BCD switches, I did not realise that they came in anything else than thumbwheels or screwdriver set versions. Unfortunately there is very little choice and they are quite expensive.
Thank you KMoffett for that link to the 7217. I dont think it will do as I really want a six digit display and a quick look at the Datasheet makes me think that it will only serve a 4 digit display timer .Also I could not find the 7217 Ic in Farnell,Jaycar,RSonline or Altronic catalogues
My biggest problem is not so much getting the bits together, but not having to source from too many suppliers, and basically I want to restrict my sourcing to Australia to cut down on postage and handling cost.

Cheers RH
You could cascade 6 each 4510 Cmos decade counters, they are presetable and are available thru Jaycar. Here is a circuit that I built several years ago that has 3 cascaded and drives a LCD display, bu the circuit could be modified for more digits.
 

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