PIC 16f777a vs 555 timer

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.

Hi,

You will not be able to get times of over 10mins accurately with a 555 unless you use additional chips.

Using a Pic can be controlled using simple switches to select you time periods and leds to show its running and alarming etc, you do not have to use a lcd.

A small MN1604 type 9v battery and 5v regulator will work for a good few hours.

Plenty of examples all over the web though they generally use a lcd, here are three I found straight away
https://embedded-lab.com/blog/?p=4069
**broken link removed**

Wp100 said:

You will not be able to get times of over 10mins accurately with a 555 unless you use additional chips.

Click to expand...

What additional chips do you meant? Mind to explain more?

So, if I don't want to use lcd as display, i can use LED instead?

From the 1st link, the user select the time interval from 0-99 min using Unit and Ten minute switches. Does that meant, I need to do this too? Can I directly have 4 switches to indicate the different time interval (meaning user can straight away select the button, & countdown automatically?

From the 2nd link, it uses delay. In my project, I don;t wish to set the time for delay, but the timer continue to countdown again after I switch off the alarm after the 1st countdown. And is it possible to use the same coding in MPLab (of course with some changes of the number)

Hi,

A 555 is not suited to long timing periods, so for 10 min + its better to set the 555 as a 1min timer and use additional chips to count the 555s 1 min output pulses to create the required output times.
A 4017 decade counter is a typical choice.

Thought that third link was almost exactly what you are after, with just simple switches and led instead of compilcated lcds.
The progam will easily convert onto a 877a chip and they will all work in MPlab .

You have now added more parameters to your program saying you want it to automatically do another countdown after the first.

Suggest you look at all those code examples and then sit down and write you own program - its the only way to learn.


All those examples are using Assembly code, there are other languages, primarily C which you might find easier.

Give things a try, if you get stuck you will always find help here.

To get going start off with the typical flashing led routine, good tutorials here.


https://www.electro-tech-online.com/threads/directorial-antenna.467/