Hi everyone..
I wanted to come up with a circuit that acts as a reminder. The general concept is that when I turn ON the switch, the timer will be triggered. After selecting the time interval, timer starts to coundown and a buzzer will beep to remind me that my time is up. I have to turn OFF the switch or else the buzzer will remain beeping.

At first, I intend to use NE555 timer, piezo buzzer,9V battery and microswitch.
The time interval is set to 10mins, 15 mins, 20 mins and 30 mins (4 different buttons)

But the problem is the time accuracy..So, I wanna try to use a PIC16F877A and MPLab for the coding .

My questions are:
1. Is it a must to have a lcd display in my circuit? (Because when I refer to past tutorials, most use a lcd display.)
2. Is 9V battery sufficient to run it?
3. Is there any similar circuits or coding that I can refer to?


Thank you for any helps and sorry for any mistakes because I am new to electronics and circuit.

 

Strictly speaking you do not need a LCD. You can use LEDs to indicate what is going on. You could use a 9 volt battery. But that will require a voltage regulator. And a 9 volt battery will not last very long. Maybe it is better to use a battery pack with 3 1.5 volt batteries. If you have some old 5 volt cell phone charger this may also used. Regarding the coding. It is bette you do your own coding. And ask us for help then you are stuck. I will recommend using C. You can also download a free C compiler from microchip.

 

Maybe you have a box of 16F877A's and you want to find uses for them. But that's a 40-pin component, and you really don't have a demanding application there. If you need the kind of accuracy you can get with a crystal oscillator, then a 14-pin chip would do the job. If something like 1% time accuracy would be enough, then I don't see anything wrong with an 8-pin processor.

9-volt batteries aren't good for much. As t06afre said, 2 or 3 AA or AAA cells would be a better plan (but check what voltage your buzzer needs--that may force you to use 3 cells even if the processor will run on 2).

 

3V Lithium button cells are also good for such circuits.

Maybe OP has a 16f877 available. Crystals are cheap. Some new PICs have internal oscillators.

 

The hardware connection is easy. You can connect 5 button switches for 10min, 15min, 20min, 30min & "Buzzer Stop" to input ports. 4 LEDs and a buzzer to the output ports.

When one of the switches is pressed, the corresponding LED would flash while waiting for timer countdown. It would light solidly when the set countdown time expires. The buzzer would sound until the "buzzer stop" button is pressed. At the same time the lighted LED switches off.

The time-consuming part is the writing of software if you are not experienced.

Allen