Multiple Inputs / Outputs on 1 pair

CassLan

Quick question,

I have a situation where I have multiple alarm sensors (switches) on a roof, but only 1 available pair going down to the alarm panel (Prop based).

I was thinking of making a small board which would recieve these inputs...transmit the data over the 2 wires down to another small board which would re-expand these to the alarm panel inputs.

Would using a propeller at each end be overkill?

The existing cable is telephone cable travelling 30 floors (390ft).


Rick

Leon

How many sensors?

Leon

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

CassLan

5, but since i'm going through the trouble I would like to design for 8 ~ 16.
I was thinking of using a 4021 on the sensor side and a prop on the recieving/expanding side..but I believe that would require 3 wires (clock/data/latch).

Rick

Post Edited (CassLan) : 5/28/2009 9:05:25 PM GMT

kwinn

The propeller chips would certainly be loafing along for this application, but if you are already familiar with spin and the propeller it would make sense to use them. At the current price it even make economic sense, particularly if you have everything you need to program it already.

Kit Morton

What about using a I/O expander on the roof?

I don't know that much about them, but I'm pretty sure you can get them in I2C and other two wire interfaces. Of course depending on how far away the switches were from the alarm panel you might have trouble with the serial communications.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PHRED, FIRST Team 847, Member
Go -> PHRED

CassLan

Thanks, I've never knew they existed!

I was looking at the MCP23008-E/P (http://ww1.microchip.com/downloads/en/DeviceDoc/21919e.pdf)

I will give it a shot!

Rick

Philldapill

You can always make your own "custom" serial protocal. IR remote's, like on TV's, use a pulse modulation to send the data. From what I recall, each low-high-low transition acts as the clock, and the low period either signifies a 1 or a 0. Basically, you have a series of pulses, and the actual data is represented by the off time of the IR signal.

You could always do something like this - use one wire for ground, and the other for data/clock all rolled into one. From there, it's a simple matter of making your own protocal.

And yes, a Propeller is overkill, but at $8 a pop, so what? [noparse];)[/noparse]

hover1

Is the phone cable CAT3? (Twisted?) It seems you would need RS485 to connect the two at that distance.

Jim

James Long

hover1 said...
Is the phone cable CAT3? (Twisted?) It seems you would need RS485 to connect the two at that distance.

Jim

I actually built a project that used a 5 volt signal and it was good for about 20 meters. The wires were typical parallel cables (shielded), but it worked fine at those distances. At 3.3 volts, I probably wouldn't go over 10-12 meters.

James L

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer

Lil Brother SMT Assembly Services

Please note: Due to economic conditions the light at the end of the tunnel will be turned off until further notice. Thanks for your understanding.

CassLan

I thought about RS485 due to the distance..but that would require 3 wires, I only have 2 to work with.

Rick

Toby Seckshund

Over that sort of distance speed will have to be kept right down. What about DC? If the sensors are just switches then use a resistor ladder and a/d at the base end. Each switch will be idendifiable and interferance would not be a problem (if they are switches, that is)

CassLan

Thats simple cheap and brilliant!