interfacing multiple feild sensors with microcontroller.

[sanddune008]

Hi All,

I am designing Hub which will take in inputs from 6 sensors and based on the sensor sends control command over UART interfaced to the RS485 network.

Now how do i interface these 6 field sensors to the PIC. Which can contain at the most 3 EXT INT's.

Assuming the field sensors to be passive devices which just gives a basic trigger circuit.

Is current loop 4-20ma the way to go?

Can any one suggest a solution in the design?.

Thanks in advance

 

[Pommie]

What do the sensors give out? A voltage, pulse, frequency etc.

Mike.

 

[sanddune008]

It will receive Pulses......Basically i need to sense the pulse from respective sensors and send unique control commands to the network.

 

[sanddune008]

It will receive Pulses......Basically i need to sense the pulse from respective sensors and send unique control commands to the network.

 

[blueroomelectronics]

What exactly are the sensors?

 

[Pommie]

If it's just pulses then use something like a 16F690 that has 10 interrupt on change pins.

Mike.

 

[ccurtis]

What is the distance between the sensors and the PIC? How are the sensors powered? Yes, what are the sensors?

 

[sanddune008]

I am sorry with misaddressing by defining sensors.....I will connected multiple switch inputs when the switch is closed sends a pulse. eg : activation of multiple door bells

Distance is again a grey area....roughly around 100mts diameter.

All i need a edge trigger and a way to define the exact source from were i am receiving.

As you can see that the physical device is totally dumb.

It would be wonderful if someone can give a right direction.

Thanks to all in advance....

 

[ccurtis]

Do you have two available I/O pins on the PIC? or even one will work.

 

[Pommie]

If you only have 6 push buttons to read then use a 16F690 as I suggested earlier.

Mike.

 

[sanddune008]

Thanks for your time........

Do you have two available I/O pins on the PIC? or even one will work.

I am using PIC16F628A which has just one EXT INT and about 8 -10 I/O pins.

Can multiplexers be used for the same....but by doing this identity of the source generating the pulse is not known......as i need the identity to send specific control commands.

Thanks to all........

 

[sanddune008]

If you only have 6 push buttons to read then use a 16F690 as I suggested earlier.

Mike.

Thanks for your time.

But this will involve me to poll for the push buttons status.....that is not i what i want........

This how it is : I have 4 doorbells at different locations . Now when a bell is pressed i need to know which bell is pressed and send a specific command to all the end device connected to the network.

So i have introduced a hub. And struck how to proceed.

 

[ccurtis]

Okay, when I asked if you have one or two I/O I was under the impression from your first post that you had three INT inputs, not one. I also see that you are looking for an edge meaning that you must respond to the switch closure instantly, rather than waiting for a poll of the switch to detect a closure? Perhaps because the switch does not remain closed long enough for a poll detection, or because the response to a closure must be very fast?

 

[Pommie]

The reason it's called interrupt on change is because it, ermm, interrupts.

Anyway, what is wrong with polling? What else does your "hub" have to do?

Mike.

 

[sanddune008]

Okay, when I asked if you have one or two I/O I was under the impression from your first post that you had three INT inputs, not one. I also see that you are looking for an edge meaning that you must respond to the switch closure instantly, rather than waiting for a poll of the switch to detect a closure? Perhaps because the switch does not remain closed long enough for a poll detection, or because the response to a closure must be very fast?

Exactly you got my problem.....

I am struck......changing the PIC won't be a problem.....but that is not the solution.

 

[ccurtis]

I am pretty sure that you can poll six I/O pins fast enough to detect a manual push of a doorbell switch. A manual switch closure and then release involves tens of milliseconds of closure time to complete.

 

[Pommie]

This how it is : I have 4 doorbells at different locations . Now when a bell is pressed i need to know which bell is pressed and send a specific command to all the end device connected to the network.

I missed the fact you were using a 16F628. However the 628 also has interrupt on change on the top 4 bits of port b and so could be used to read 4 push buttons. With a bit of ingenuity you can easily make an array of 4*4 switches produce an interrupt when 1 or more are pushed.

Maybe you should explain what you are trying to do as push buttons are normally so slow that polling would be easily fast enough.

Mike.

 

[sanddune008]

Thanks for your time......


See it need not be a switch all the time...it could be a any trigger pulse to the PIC input. Ex: a trigger pulse from an existing Fire alarm device(tapping the signal to my PIC). or any device that can trigger a pulse.

Can 82c59 PIC (programmable interrupt controller be used for the same)....to logically increase the No: of interrupt lines.If so does anyone have any schematics for the same.

 

[ccurtis]

Thanks for your time......


See it need not be a switch all the time...it could be a any trigger pulse to the PIC input. Ex: a trigger pulse from an existing Fire alarm device(tapping the signal to my PIC). or any device that can trigger a pulse.

Can 82c59 PIC (programmable interrupt controller be used for the same)....to logically increase the No: of interrupt lines.If so does anyone have any schematics for the same.

The 82c59 seems like overkill for your application, but I suppose you could use it to do the job.

I'm thinking six edge-triggered flip-flops (like the 74HC175) to capture and store an edge event. Present the output of the flip-flops to your I/O pins directly, or follow with a multiplexer so that you can identify and route the stored event into one of 3 interrupts.

Those hundreds of feet of cable are a definite design consideration. A cable that long is subject to picking up all sorts of EMI and triggering an event. The cable should be twisted shielded pair and a schmitt-trigger, and or other input conditioning scheme should be placed in front of the edge storage function.

 

[davidbear]

Hi,

You might try putting a 555 timer used as a "one shot" on each button so that the PIC will see the initial signal as an interrupt, and then have enough time to poll which timer is still high.