8 * 8 relay matrix connection and functionlity

Discussion in 'Embedded Systems and Microcontrollers' started by cktcrazy, May 10, 2011.

  1. cktcrazy

    Thread Starter New Member

    Mar 27, 2011
    16
    0
    hello

    i am doing the relay connection for 64 relays in matrix . i want to use 2 port of at89s8252 to connect 64 relays. i want to 2 ULN driver for this purpose. I have the circuit diagram which i got one of my friend .
    But i can't understand which pin of a 5 pin relay would connect to row and column . From the circuit diagram ,how much understand i don't know, the common pin of relay pin is connected to one pin of ULN driver and another
    normally connected pin is connected to one pin of the other ULN driver .
    Here i can't understand how the supply pin of relay would be connectded
    to the ULN driver pin.

    I have attached the circuit diagram .PLZ go through it.

    and help me in this regard. Its very urgent .Waiting for ur response

    regards from cktcrazy
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    A 5-pin relay is made up of two coil connections and three contact connections.

    I have labeled the coil connection as 'R' and 'S' and contact connections as 'a', 'b' and 'c'.

    You only need to connect the 'R' and 'S' pin to the two driver ICs as shown. The contact pins you then can be used to drive other circuits as you wish, it does not need to be connected to the multiplexer connections.

    [​IMG]
     
  3. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    How many of these relays need to operate simultaneously? And what is their normal rated voltage?

    If the answer is "potentially, all of them" and they're rated for 24 volts, and you plan to use a 24V supply, then this cannot work.

    Maybe someone can show how I'm wrong, but it seems to me that the relays can't be driven with more than a 1/8 duty cycle, and that means that the power supply must 8 be times the rating for the relays. So for 12V relays, 96 volts. So you have to choose your driver chips accordingly.

    But if the scheme is that you only need to operate 1 relay at a time, out of the 64, then it's very different.
     
  4. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    The relays aren't multiplexed so there is no duty cycle involved and 24 volt relays will work perfectly well from a 24 volt supply.
    To turn any single relay on set the column that the relay is connected to high and the row that the relay is connected to low. To turn all the relays on you set all the columns high and all rows low.
     
  5. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    OK, now I want to turn on 8 relays out of the 64. The 1st relay in the 1st row, 2nd relay in the 2nd row, so on down to the 8th relay in the 8th row. Which sources and sinks get turned on to achieve that?
     
  6. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    Point taken, my error! :mad:
    As you suggest the circuit is only good if you want to turn on one relay at a time. If you need to turn on a number of relays simultaneously then you can't use a matrix arrangement. You either need 64 port pins or a 6 line to 64 line decoder.
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    Spoken like a gentleman. However, I do think the matrix arrangement can be used. It does involve scanning and multiplexing, and I think it has to be done with high voltage because each relay would only be powered 1/8 of the time. Depending on the frequency, that might lead to other problems with buzzing of the coils. In addition, each coil would need 2 diodes, one for free-wheeling and one to make sure current goes only one way. So I wonder if it's ever going to be worth doing.
     
  8. cktcrazy

    Thread Starter New Member

    Mar 27, 2011
    16
    0
    hello

    can u plz confirm me about the working principle of UDN2982A driver . is it work the same as that of ULN driver . i ve gone through tme the manual of UDN2892A .bcoz ,here i ve problem regarding the programing logic to drive a single relay

    regards from
    cktcrazy
    thanks
     
  9. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    They are not the same!
    For the UDN2982A, logic high on any input pin will switch +Vs through to the corresponding output pin.
    For the ULN2803 a logic high on any input pin will switch the corresponding output pin to earth (Vss).
    So to turn on a specific relay you need to output a high on both the column and the row that attach to the desired relay. All other columns and rows must be held at a logic level low.
     
Loading...