32 channel micro relay board

Discussion in 'The Projects Forum' started by jismagic, Jun 15, 2015.

  1. jismagic

    Thread Starter Member

    Sep 7, 2013
    77
    0
    Hello guys,

    Anyone can suggest 32 nos relay board smallest in size. I drive the relay using arduino and loads can drive only upto 100mA per channel.

    thanks
    Jis
     
  2. Brevor

    Active Member

    Apr 9, 2011
    279
    54
    There are relay boards on EBAY, I don't think they have 32 channel boards but you could use 4 8 channel boards.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    What load are you driving that you need relays?
     
  4. jismagic

    Thread Starter Member

    Sep 7, 2013
    77
    0
    The load operates at 12-18V at 50mA. I want to put it in a small box (50*30*20cm) with arduino board. The relay boards avaialable are big
    for me. Any ultra mini sized relay boards available?

    thanks
    jis
     
  5. JWHassler

    Member

    Sep 25, 2013
    201
    33
    This one is 18cm x 9cm x 2cm. Not hard to fit two of them.
    Did you maybe intend those dimensions to be in millimeters?
     
  6. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,145
    204
    You may have to make one. Look for OPTOMOS relays. They are basically solid state devices.
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    But do you need the isolation of a relay or could a transistor switch be sufficient?
     
  8. jismagic

    Thread Starter Member

    Sep 7, 2013
    77
    0
    Physical isolation is desired.
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,805
    833
    And once again, a plea for help for some mysterious purpose, with details obtained like pulling teeth.

    @jismagic, you might get better help if we understood what it is you are working on.
     
  10. jismagic

    Thread Starter Member

    Sep 7, 2013
    77
    0
    I need to use an arduino/Teensy/ any duino to control a bank of switches that will connect and disconnect a dc voltages, 0V-20V, source/sink current a maximum of 100mA. I want the entire setup to be size of 4 arduino boards if put together to form a square. Having 32 relays are bulky.So, I cannot use them unless they are micro sized relays. SOlid state relays are very costly.

    Can I use one in the below link

    http://www.maximintegrated.com/en/products/analog/analog-switches-multiplexers/ate.html

    High-Current CMOS Analog Switches?

    or

    http://www.maximintegrated.com/en/products/analog/analog-switches-multiplexers.html

    Can I get perfect isolation as in relays using above.

    Anybody has suggestions?

    thanks
    Jis
     
  11. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    None of those analog switches have isolation.
    For isolation you need solid-state or mechanical relays.
    How about one of these?
     
  12. jismagic

    Thread Starter Member

    Sep 7, 2013
    77
    0
    Solid state is costly and 32 of them make it not cost feasible.
     
  13. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    How much do you expect to pay for relays? That SSR looked pretty reasonable to me.

    And as others have said several times, if you would better describe the whole scenario, you would get better advice.

    What are the loads? Not just volts and amps, but what? Leds, inductive loads, what? And what is the switching plan? Is only one on at a time, or do they work in groups, or in totally random patterns? Answers to these questions might open up possibilities with multiplexing, etc that can't be seriously considered without better background info.
     
  14. jismagic

    Thread Starter Member

    Sep 7, 2013
    77
    0
    it is small sized ATE (automatic test equipment). It will be connected to a electronic device which has many discrete inputs - 18V dc max, active high and active low inputs. The loads are just resistance or set the discrete input of the device high or low state. My Test equipment either source the device for active high state or sink for active low state.
    My budget is around 100 USD for supporting 32 switches.
    If i m not still explaining properly, I would perhaps draw a diagram.
     
  15. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    Some of those I referenced are about US$2 which is likely less than the cost of a mechanical relay.
     
    Last edited: Jun 23, 2015
  16. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    Does the device being tested provide the 18V which will be switched by the relays? If not, things won't be truly isolated anyway, in which case it seems like you could make 32x 18V push-pull outputs with transistors of some sort much more easily and cheaply than relays or SSRs.

    If you do go with relays, you'll likely need something between them and the Arduino. At the very least flyback diodes, and probably transistors of some variety to handle the coil current. So be sure to include all related circuitry when comparing relay cost to SSR cost.

    My money's on crutschow's solution. Or if it has to be cheaper, maybe you compromise on isolation requirements and your options open up.
     
  17. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,045
    3,811
  18. jismagic

    Thread Starter Member

    Sep 7, 2013
    77
    0
    The power source that will be switched by relays and that operates the device under test are same. the idea of isolation comes from the requirement that in no way the device under test is influenced by arduino and related circuitry.
    Did you say that, if I use SSR, I will not require any related circuit around relays and can be directly driven by arduino?
    thanks for reply.

    jis
     
  19. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    Yes, a typical SSR can be directly driven by an Arduino.
    For example, the inexpensive SSR device that GopherT referenced has a minimum input ON voltage of 3.75V with a 1kΩ nominal input resistance.
     
    ebeowulf17 likes this.
  20. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    You could certainly drive a number of them directly with an Arduino, but not sure how many. First off, depending on which Arduino you're using, you won't have enough GPIO pins to drive 32 SSRs directly, but there are I2C IO expanders and shift registers available pretty cheaply - either one if which will easily add the additional capability if you need it.

    The other potential issue that comes to mind is total current draw from the Arduino GPIO pins. You'd need to check the specs on whichever board you've got, but as an example, the Uno can provide max of 40mA per pin, but only 200mA total for all IO pins, so not all pins can be sourcing current at once at such high levels. After a couple quick searches for example data, I strongly suspect this won't be an issue for you. Using the SSR example above, a 5V output into 1k input impedance would be sourcing 5mA. Even with all 32 outputs active at once, that would be 160mA. If you are using expanders or shift registers, they'll have their own current sourcing capabilities to factor in. And of course, if you only activate a small number of pins at a time, it definitely won't be a problem. So, probably not a problem, but something you should verify with the specs of your specific board and whichever SSR you choose.
     
Loading...