RS485 to TTL Circuit Needed (can pay)

[Fatima Peredo]

Hi,

I need a simple device based on a PIC that will connect to an RS485
network and output 20 TTL compatible digital outputs. I know it's
simple and I could probably design one myself, but I'm sure this must
have been done before. I've searched the Internet but I only seem to
find RS485 boards that also have analog inputs or other features added
on I don't want or need.

If someone knows of such a product, I'd be very interested. If not, I'd
be willing to pay a fee to someone to design one (or modify an existing
one they know about) for me.

Thanks in advance.
Fatima

 

[Phil Hobbs]

I need a simple device based on a PIC that will connect to an RS485
network and output 20 TTL compatible digital outputs.

This isn't a very specific description. What sort of RS-485 network,
using what protocol, and what do you want the digital outputs to do?
Twenty resistors connected to +5V would satisfy the spec you've written.

Cheers,

Phil Hobbs

 

[Robert Monsen]

http://www.rs485.com/

 

[jake]

I have a similar need but mine is to read analog signals via half-duplex
RS485. The PIC16c773 looks like it would fit the bill nicely, 12-bit ADC
and few external components needed. I'd want to send out an ASCII request
to a specific RS485 address, i.e. "GetData 137",and have the six readings
come back in one CSV string (137, ad0, ad1, ad2, ad3, ad4, ad5). I've never
done PIC before so was considering using one of the Basic 'compilers' to
program it, I thought Basic would be sufficient considering this is not a
very demanding app. Any thoughts, advice, bids (via email)?

thx, jake

 

[Fatima Peredo]

I haven't decided on a protocol yet, but the devices will be connected to
an embedded PC (I also haven't picked which one yet). There will be 18-20
of these devices connected to a single RS485 line and of course each one
will
need to have its own "address" so I can send data to a specific device.

The 20 digital outputs are going to a couple of circuits which will do
various
actions depending on the data. Two of these are comparators and the other
two are counters. They use this digital data to make a decision on when to
activate another devide.

I already have these other circuits which require the 20 bits of information
as inputs. Each of these circuits (devices) is separate, so using a single
board with say 60 outputs (20 to each of three) is not practical.

I have been to various RS485 sites and have seen several products but
none that would do what I want specifically. As mentioned previously,
I don't need A/D, counters or timers so purchasing an RS485 I/O board
with these features is a waste of money.

Fatima

 

[Phil Hobbs]

I haven't decided on a protocol yet, but the devices will be connected to
an embedded PC (I also haven't picked which one yet). There will be 18-20
of these devices connected to a single RS485 line and of course each one
will
need to have its own "address" so I can send data to a specific device.

The 20 digital outputs are going to a couple of circuits which will do
various
actions depending on the data. Two of these are comparators and the other
two are counters. They use this digital data to make a decision on when to
activate another devide.

I already have these other circuits which require the 20 bits of information
as inputs. Each of these circuits (devices) is separate, so using a single
board with say 60 outputs (20 to each of three) is not practical.

I have been to various RS485 sites and have seen several products but
none that would do what I want specifically. As mentioned previously,
I don't need A/D, counters or timers so purchasing an RS485 I/O board
with these features is a waste of money.

Unless you're going to be needing a whole heap of these things, you'll
be much better off with a purchased solution, no matter how many bells
and whistles it has. Designing and building a one-off will cost
thousands of dollars if you pay someone else to do it. OTOH, you could
do it yourself, save a lot of money, and learn some useful skills.

Cheers,

Phil Hobbs