Direction on building a serial relay interface 1

[mixali]

I'm wanting to build a interface card that can control around 20 relays. I would also like to have the same amount of inputs. I'm wanting to build an interface with VB to control these relays. Also the inputs wiould be used to trigger events which vb would interperate to set the appropriate relays. I have found many different cards available however none with the amount of inputs and relays. I was thinking of building my own and was wondering if anyone had already done this and could give some advice. I'm looking at different controllers ie pic, atmel and basic stamps however it would be could if someone could point me in the right direction.

cheers

P.S I would like to the vb app to be able to query the card onstartup to determine the status of all relays.

 

[cbarn24050]

Hi, I presume you wish to control it via a com port. In that case its quite a trivial program for a micro. The 8051 would be the easiest and cheapest, nearly all the software is free.

 

[djs]

Hello;
You can buy diecrete I/O cards using standard serial communications. For example see the following URL:

http://www.proconel.com/modmux.htm

 

[skills]

Atmel AVR family has nice processors for stuff like this and you can use C or basic compilers that are very cheap like $80. I like the 8535 or 8515 myself.

 

[jtykka]

Easy way to control some relays from VB is do it from LPT-port. If you have win95/98 there is no problem, you just set port signal on/off. I have made one stupid dll for this several years ago.
If you'd like to have more relays than there are outputs, use multiplexing. Put some 'serial in sift register latch' chips. Then you need just three lines to control so many relays than you need (clock,data,latch).
If you use NT or Win2k then it's more complicated cause kernel doesn't allow you to write directly into LPT port, you meed device driver instead. I have seen one non commercial driver somewhere. If I find it again I'll post address.

 

[jtykka]

Here is something

http://www.lvr.com/parport.htm

 

[ChefGroovy]

I made a board similar to what you want. Control 147 24v pnematic solonoids via par port. The logic is extremely simple. using 74259 and 74154 decoders and 75468 drivers, to control the 24v

I have a partial schematic drawn up if interested.

jdshaffer@qx.net

 

[plcsavvy]

I would use a BSII micro controller from parralax INC.and a stamp I/O extender that may be available from Scott Edwards Electronics. Next, I would purchase the book "SERIAL PORTS COMPLETE" Written by Jan Axelson of Lakeview research INC.
Her book is one of the most comprehensive, regarding the subject of serial ports. The book explains how to use Visual Basic to to form a serial interface using the MS COMM active x control that comes standard with VB 6.0