Digital egg timer

kdouglas

hey, not exactly an engineering question, but there's no electronics forum, so figured this would be the best place...

im looking to build a digital egg timer, with a display showing how much time is left and a buzzer which will go off once the timer hits zero, something along the lines of this is pretty much what i need, except with a display, is it possible to modify that circuit to connect a display, or can anyone point me to a site which might have similar circuit diagrams etc..

been looking on google but cant find much

robfitz

I think your going to need to use a microcontroller for this, something like a PIC will do. So the PIC will handle all the logic, the code will have to work something like this:

Wait for the start/power on button to be pressed.
Set a counter for the number of seconds to cook the egg. Set the timer interrupt for one second. Reset the time on the display.
The timer code will be called once a second. Decrement the counter. If the counter is zero stop the timer and trigger the buzzer. Else update the time on the display.
Wait for the stop/power off button to be pressed.

You will need to use some electronics to interface a button or two, a 7-segment display and a buzzer to the PIC.

It should be possible to code up the following in assembler, C or Basic depending on the PIC and development kit you use. You may find one that includes the extra electronic parts you need. This PICkit 1 FLASH Starter Kit from Maplin might be useful, but you should do some more research before you buy.

You might also want to pickup a book on the subject. I haven't read this book 123 Pic Microcontroller Experiments for the Evil Genius, but I have read some of the others in the Evil Genius range and I found them very useful, and it's under 10 pounds from Amazon.co.uk. Maplin and Hodges Figgis also have a limited selection of electronics books in there shops in Dublin.

Michael Collins

Yep I agree with robfitz, a microcontroller is the way to go. If you're thinking of using an LCD, it's the only way to go!

If you're using 3 7-segment LEDs for the display you could get away with connecting a few logic counters together, and you'd avoid learning loads of assembly code (although learning it wouldn't be a waste of time, microcontrollers can do almost anything!). You'd then use maybe a 555 timer combined with an RC circuit for the countdown. (Although an RC circuit timer won't give great accuracy - talking about an accuracy on the order of a few seconds.)

kdouglas

thought i might need a microcontroller alright, some excellent info there robfitz, thank you

it's been about 2 years since i did any assembly (on the 8086) but i know enough to pick it up again. Or if the development kit can use C, that'd be handy.

It's really just for a small project that I had in mind, didnt want to spend too much on it, but after my college exams next month, i think i might actually get a starter kit and have a mess about, are the kit's normally about the price of that one on maplin (STG£40) or would you pick one up for cheaper?

Michael Collins: i like your idea with the logic counters, would probably work out a bit cheaper, ill have to do some research into it though, my electronics design is a bit rusty, havent done it in a few years