Need Help Digital egg timer

Thread Starter

eiji116

Joined Oct 14, 2007
9
i need a build a digital egg timer and the required time will be set on the switches and then timer will be started. At the end of the time period, a buzzer will sound for 2 seconds and the timer will reset

i can only use the following intergrated circuit

4029 - Presettable up/down counter.
4093 - Quad 2 input Schmitt triger.

kinda lost and don't know where to start:confused:
 

Thread Starter

eiji116

Joined Oct 14, 2007
9
after reading the datasheets still kinda confused i know what each pin does now but still don't know where to start
 

SgtWookie

Joined Jul 17, 2007
22,220
Are you limited as to how many 4029's you can use?

What time intervals are you supposed to be able to set?

You can use one of the 4093 NAND gates as a clock signal generator.

Connect the two inputs of one of the gates together. Put a capacitor between the two inputs and ground. Connect a resistor between the output and the inputs. Presto, a clock signal will be on the output, and a wave resembling a sawtooth will be at the input.

This works because when the two inputs are tied together, the output will be the NOT equivalent of the input. If the inputs are at a logic LOW level, the output will be at a HIGH level. Current will flow through the resistor tied to the inputs, which will charge the capacitor until the HIGH threshold is reached. This changes the state of the output to a logic LOW, discharging the capacitor through the resistor until the LOW threshold is reached, forcing the output to HIGH. Repeat.

Use Ohm's Law with the relevant datasheet items to determine what values of R and C to use.

R must be large enough to limit current to stay under the maximum current rating. 10K Ohms or higher would likely be a good starting place.
Adjust your value of C to get the range of time.
You already know that you need a 2-second timer for the beep, so work out the values for a 2-second clock.

IMPORTANT: ALL unused inputs to a CMOS device must be "tied" to either a logic "HIGH" or logic "LOW" level. Otherwise, the inputs will "float" unpredictably, generating lots of electrical noise.
 

Thread Starter

eiji116

Joined Oct 14, 2007
9
no limit to the 4029

the time interval is around 2-6mins and evrey 1 min interval, so like 2min 3min 4min 5min 6min

and thingmaker3 thx for the great datasheet it really helps alot
 

SgtWookie

Joined Jul 17, 2007
22,220
Gee, I searched for 4093 on National's site, and it didn't come up with that particular datasheet. Thanks, thingmaker3 ;)

OK, so use the 4093 to make at least 2 clock pulses; one for 2 seconds, another for 1 minute. That'll give you up to 16 minutes in binary mode, or 10 in decimal mode.

If you use it in count up instead of count down, you can use the carry-out to trip your alarm. Instead of presetting the counter with the number of minutes to wait, set it with the seconds you don't want to count (ie: if you're in binary mode, and want to time an egg for 3 minutes, preset the counter to 13. After three minutes, carry out will toggle to low.)
 

Thread Starter

eiji116

Joined Oct 14, 2007
9
R x C = T so if i want a 2second clock pulse i need 20K x 100uF = 2secs something like this right?

have alook at the attachment see if i'm on the right track

but i'm still kinda confused on the 4029 up/down counter don't really know how to set the counters

thx
 

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