C code example for relay control with PIC16F887 in time switch project

Hi. So far the project is working in the LCD thus the time set is able to be displayed on the lcd using switches. So my problem is on the load, when the relay is energised it must close the Normally Open contacts(NO) so the Load, eg BULB connected in series with the contacts will light, snd when the relay is de_energized it must open the contacts hence the BULB will be OOF. So the relay is interfaced with PIC 16F887 Microcontroller, so i need a C program of the the relay interfaced with Microcontroller(PIC16F887).

I would ask that as a courtesy to us, who are sacrificing some of our time to help you, that you Proof-Read your submissions before hitting the Submit button. You are expecting us to spend some time on you -- have the courtesy to spend a little of your time Proof-Reading, please.

Read, both, to eliminate typos, _and_ to make sure your submission is clear, complete, and readable. For instance, it's unclear what you're asking. You say the project has a working LCD that displays the "time set" (by that I assume you mean "the timer 'ON' duration"). Then you say you need a C program to drive the relay coil. That implies that there, currently. isn't a C program. If so, what is driving the LCD display? And, wouldn't the C program also need to access the same information that is being displayed on the LCD? And wouldn't the C program also need to monitor some instigating factor--i.e. something to begin the timing event--like a push button, or something?

Also, you don't specify if an output high will drive your relay circuit to close it's NO contacts or if a low is needed. Also, which output pin will you be using.

You know, stuff like that ;)

Thank you

["...the BULB will be OOF" like it got punched out or something, so I assume you'll be using servos and boxing gloves and such...and won't you have to replace the BULB after each timing interval?!?]

Yes no worries can we have schematics please etc etc and then might just be able to asist
Cheers
Mark

Hii pisto, i think you have a problem working with the relay & interfacing it with PIC.
i have attached a proteus file which might explain you the working of relay.
i have attached a motor which requires 12 volts, but you can connect a bulb to the relay terminals & apply the required voltage.
if you want to interface this with microcontroller you must use a transistor. use this transistor as a switch. i have chosen the base resistor value in such a way that the current fliowing through the base is 1/10th that of collector current. don't go into that. If u want to glow the bulb u must send a High signal to the port pin where you have connected the transistor or send a zero to turn off the bulb.
if you have connected the transistor to porta pin 0 then ur command should be like
porta0_bit=1; //this will glow the bulb
porta0_bit=0; //this will turn the light off

make sure you are using the port as digital ports otherwise your code will not work. To make sure you are using the ports as digital, read the DATASHEET.
ALL THE BEST!

You need to be carefull with relays and pic devices one of the main problems that you encounter is electrical transient noise or if you like back emf or induced emf in pcb tracks

The result of relays energizing de energizing

Alot of this can be overcome easily by using optocouplers The normal effects are spuradic reset of the micro and some very other obscure problems which can be a real headache when fault finding Apart from just eliminating this type of problem with pic cpus by using opto couplers You also protect the ports of the pic cpu by providing isolation which in turn means that should relay driver trannies fail then at least in the case of collector base short circuit You dont damage ports

12volts or higher fed to portb c d etc The advantage is higher switching speeds can be attained Consider here base emitter capacitance I also recommend using 33pf to 100pf on supply lines into relay coil and out of coil with diode strapped across relay coil to prevent back emf damaging driver circuitry

Just general tips gained from headaches having done some of this myself and having to find out the hard way

Hope this helps you

Mark Harrington

Also, run separate lines from the supply point (i.e. output of regulator, battery terminal, battery connection to PCB, filter cap, etc.) to the PIC regulator and to the relay coil. That way you provide isolated current paths to each. Also, if there's a regulator suppling the coil voltage, then good to include a capacitor on the output of that regulator (consult the regulator datasheet for improving "transient response").