Shop OBEX P1 Docs P2 Docs Learn Events
ULN2803 or ZTX605 ?? — Parallax Forums

ULN2803 or ZTX605 ??

BronsonBronson Posts: 44
edited 2005-05-15 03:52 in BASIC Stamp
Hi,

I am just successfully finished my project with BS2 that controls 220VAC mechanical relays/loads by using ULN2803. I did have 'BS2 HANG' problem caused by some kind of noise and/or interference but had been fixed by putting caps across the relays' input coil.

And I just purchased BSIO16 board from Parallax, the board uses ZTX605 instead of ULN2803. I've tried the board on the same project and there is no noise and/or interference problem at all.

My question are =
1. Is ULN so fragile to use when it comes to 220VAC loads?
2. Are there any other conditions ZTX605 is better than ULN? If possible, I would like to avoid ZTX605 due to board design complexity, and I couldn't find ZTX605 in Indonesia.
3. Should I use ZTX605 or ULN2803 for the same next project?

Thanks,
Bronson Alex

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-05-13 04:59
    Bronson,

    ·· If you fixed the problem you were having then don't worry about switching.· You're going to find that certain combinations of parts may need certain provisions to work properly.· This is especially true of noisy devices such as relays and motors.· Often the solution is simply a capacitor (As you found) or a diode.· But sometimes it can be more.

    ·· Use the ULN, and just be aware of the precautions you need to make when you build the project again.· Especially if the other part is difficult for you to get in your area.· Many people use the ULN chips without issue.



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Alan BradfordAlan Bradford Posts: 172
    edited 2005-05-13 10:38
    Hi Bronson,

    I agree with Chris, If you fixed it dont worry about it.

    I switch 120/220/480 volt relays, solenoids and transformers with Stamp based circuits all the time.

    The problem you are/were having most likely is not a·weakness with the interface chip, but with the Relay coil and its power supply. The cap you added across the coil filters out the spikes caused when the coil field collapses during shut off. This spike can get back into the power supply and if it is a common supply with the Stamp, it can lock up the stamp. Sometimes isolated power supplies can be effected.

    I try to keep my DC supplies seperate. It costs a little bit more, but in the long run it is more reliable. If you cant split the power supply, then run the relay power before the regulator·for the Stamp. Add a .01uf and a 300uf Cap across the output of the power supply/regulator feeding the Stamp.

    When in doubt, add filters.

    Alan Bradford

    Plasma Technologies
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2005-05-13 10:39
    The ULN2803 has build-in suppression diodes -- but they only come into play when you connect pin 10 to the positive side of your relay coils. Did you do that?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Jon Williams
    Applications Engineer, Parallax
    Dallas, TX· USA
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-05-13 14:40
    And, I read somewhere that if you use separate supplied, they should only be linked by one ground connection as you can get some nasty misbehaviors due to have multiple ground paths. So, keep it clean and simple to avoid trouble.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    G. Herzog in Taiwan
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-05-13 17:00
    ·· Alan states some good points/preventative measures for controlling high-voltage circuits.· Some things to keep in mind.· As for the common ground thing, even with separate supplies and only a common ground, noise can be introduced through ground, or even through the air as EMI.· One way to isolate circuits is to use an SSR (When applicable) or to use opto-couplers and drive the Relay from the target's supply.· This will protect the controller from much of the noise generated by Relays and solenoids.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • BronsonBronson Posts: 44
    edited 2005-05-14 11:27
    Thanks for the responds.
    For Chris and Alan, could you give me the rough schema/diagram of your idea (for better understanding since my English in technical terms and electrical background is limited) ?
    From the way you clarify my problem, it seems that you guys really understand my nightmare (I spent 3 weeks in finding the answer before I found the caps' soultion).

    For Jon, you were already involved 'indirectly' since my first project with BS until now. Thanks, Jon.

    Regards,
    Bronson ALex
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-05-15 03:52
    Bronson,

    ·· The specifics of the circuit really depend on exactly what you have connected at any given time, as well as the voltage, current, etc.· So there are too many factors to generalize.· If you know you want to control a relay with the Stamp Module, you find out it's coil voltage, coil resistance, etc.· Then you decide the best way to drive this particular relay.· Obviously a solenoid would have to be looked at a little differently.· So it's bext to do a little research.· There are tons of circuits out there for doing this, but not all work properly in every situation.· Most of these type of devices simply require a diode in reverse across the coil.· Sometimes you need a capacitor to clean up noise.· The size depends on whether the noise is high frequency, or low (voltage dropout).· Head spinning yet?· tongue.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
Sign In or Register to comment.