Post by thread:[OT] RS485/RS422

Mike Montalvo wrote: > I am using RS232 drivers/receivers to poll a 10X10 matrix of buttons. Can you clarify? Does *every* remote (button sender) have a unique line to the base? What do you mean by "Matrix"? Are you sharing RS-232 lines (paralleling)? > each button is installed in an apartment up to 150 feet away. They > are all connected with 24 gauge twisted pair telco cable. Does this cable also carry the power, or is it locally supplied by, e.g., a wall-wart? Wall-warts have the advantage of isolating the ground lines. > I put 1 output bit high and check the 10 inputs one at a time. Then > I move on to the next output bit. I scan all 100 switches about 3 > times a second. Does this imply that one transmitter at "base" sends to ten remotes in parallel and each of these comes in to a separate receiver? > I cant tell exactly how good it is because I'm constantly dealing with > people ripping the buttons off the wall, grounding them out or > connecting phone lines to them. ROTFL. Sounds par for the course. Are the offenders users or tradesmen? -- Cheers, Paul B.

>> I am using RS232 drivers/receivers to poll a 10X10 matrix of buttons. > > Can you clarify? Does *every* remote (button sender) have a unique >line to the base? What do you mean by "Matrix"? Are you sharing RS-232 >lines (paralleling)? Keep in mind I am not actually transferring 'data' per say.. The matrix is so I can get 100 different combinations from only 20 I/O lines. One side of the first 10 buttons are all connected to output 1. The other side of the 10 buttons each go to 1 of 10 inputs. (i.e. the first button goes to input 1, the second to input 2...) So now if I were to put output 1 high and I polled the 10 inputs, I would be able to tell if any of the buttons were pressed because the input would be high. Now set up 9 more outputs (each with 10 buttons) and connect the other side of the buttons to the original 10 inputs. Now I can go 1 output at a time and poll the 10 inputs. This would check all 100 buttons. For every output there is a RS232 driver and for every input there is a RS232 receiver. The MC1488s and MC1489 have 4 driver and 4 receivers, respectively, per chip. >> each button is installed in an apartment up to 150 feet away. They >> are all connected with 24 gauge twisted pair telco cable. > > Does this cable also carry the power, or is it locally supplied by, >e.g., a wall-wart? Wall-warts have the advantage of isolating the >ground lines. The whole system is in a central location. The only things in the apartment is the actual button and the 2 wires going to it. >> I put 1 output bit high and check the 10 inputs one at a time. Then >> I move on to the next output bit. I scan all 100 switches about 3 >> times a second. > > Does this imply that one transmitter at "base" sends to ten remotes in >parallel and each of these comes in to a separate receiver? Hmm, yes and no. As explained above, one driver does drive 10 lines, but they are not terminated unless someone is pressing a button, then the signal would be sent back to a receiver. Both transmitter and receiver are at the 'base'. >> I cant tell exactly how good it is because I'm constantly dealing with >> people ripping the buttons off the wall, grounding them out or >> connecting phone lines to them. > > ROTFL. Sounds par for the course. Are the offenders users or >tradesmen? Both. Its actually not an apartment building, its a state run homeless shelter in the Bronx. The buttons are mounted on the phones as the phone isn't supposed to be moved. But the temporary tenants sometimes insist that they hook up their own phone and take it upon themselves to rewire it. Or they get mad and just knock the thing clear off the wall...Since it was such a custom install, when the phone company comes they don't have a clue whats going on and have screwed things up in the past. The whole reason for the system was because the phone based intercom system we were installing did not include a way for the tenants to contact the guard. That was one of the requirements of the contract. Regards. ----------------------------------------- Mike Montalvo G-FORCE Motorsports http://www.g-forcemotorsports.com 516-794-0858

At 00:50 1/06/99 -0400, you wrote: {Quote hidden}>>> I am using RS232 drivers/receivers to poll a 10X10 matrix of buttons. >> >> Can you clarify? Does *every* remote (button sender) have a unique >>line to the base? What do you mean by "Matrix"? Are you sharing RS-232 >>lines (paralleling)? > > >Keep in mind I am not actually transferring 'data' per say.. The matrix is >so I can get 100 different combinations from only 20 I/O lines. One side of >the first 10 buttons are all connected to output 1. The other side of the >10 buttons each go to 1 of 10 inputs. (i.e. the first button goes to input >1, the second to input 2...) So now if I were to put output 1 high and I >polled the 10 inputs, I would be able to tell if any of the buttons were >pressed because the input would be high. Now set up 9 more outputs (each >with 10 buttons) and connect the other side of the buttons to the original >10 inputs. Now I can go 1 output at a time and poll the 10 inputs. This >would check all 100 buttons. For every output there is a RS232 driver and >for every input there is a RS232 receiver. The MC1488s and MC1489 have 4 >driver and 4 receivers, respectively, per chip. > So to put it simply, you have 150 feet of cable or more that is terminated (Persuming) only at one end by the receiver? Humm, sonds like an antenna to me. RS232 only has limited ESD, EMI protection on the inputs as the clamping is to the power source, and assumes that the power source is able to cope with the current dump delivered by the strearing diodes durning an overvoltage condition. You may wish to look at some form of external clamp protection TRISILS on the inputs and accross the power sources. Dennis

At 10:28 2/06/99 +1200, you wrote: >From your earlier notes it would seem possible that the button wires could >become connected to the phone line. i.e. 50V or so with all the charge >stored in the line capacitance (39-65pF/metre or thereabouts) plus the >current from the line card. >Definitely put some additional protection on the inputs! > >Richard > Not only that, you have 90VRMS battery backed ring or 75VRMS (Effective) ballanced ring! In some parts of the states you may also find that the line power is 100VDC! It is never a good idea to use telepone cable for non telephone products. Dennis >> {Original Message removed}