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Latching relay circuit question? — Parallax Forums

Latching relay circuit question?

GreenShellGreenShell Posts: 3
edited 2008-07-20 02:23 in BASIC Stamp
I am trying to send an output pulse of 25ms from P1 to a latching relay that requires more than 20ma to actuate, so directly trying to control the latching relay from the 5V pulse·source of P1·will not work. However, conecting·my latching relay directly to VIN is enough to get the relay to·switch. My question is how do I configure my Homework board to use·the VIN on a 25ms pulse from P1?·My latching relay coil works on low voltage and·actuates a·120VAC switch.

Thanks,
Mark

Comments

  • UnsoundcodeUnsoundcode Posts: 1,532
    edited 2008-07-05 22:38
    Hi Mark, this link http://forums.parallax.com/attachment.php?attachmentid=37701
    describes how to use a transistor to safely use the output from a Stamp pin to control a motor or relay.
    Another option would be to use a solid state relay (SSR), taking care to choose one that has a switching input that is within the voltage / current range of the BS2.

    Jeff T.
  • GreenShellGreenShell Posts: 3
    edited 2008-07-06 01:32
    Thank Jeff,

    I couldn't find an SSR, but I will keep looking.. Fry's and RadioShack don't carry them. I did get two small reed relays to work though. The nominal coil voltage for the reed relay·is 11ma which the BS2 has.·The·reed relay· activated· the VIN circuits·9v·which is enough to·actuate my·latching relay.··I need two reed relays, one connected to P1 and one connected to·P2 to send opposited on/off signal pulses·to the latching relay. I hope to find one·SSR to do this later.

    Thanks Again,

    Mark W.·
  • Mike GreenMike Green Posts: 23,101
    edited 2008-07-06 01:53
    Reed relays are perfectly fine. Be sure to use a diode across the relay coil with the cathode end (bar) to the side of the relay coil connected to Vdd and the anode end to the other side of the relay coil. You should use a diode across the latching relay coils as well, again connected backwards to the polarity of the power source. These diodes dissipate the energy produced when the power is turned off to the relay coil and the magnetic field collapses. This energy can cause accelerated wear of the reed relay contacts and can damage the Stamp's I/O circuitry if not dissipated.
  • GreenShellGreenShell Posts: 3
    edited 2008-07-20 02:20
    Hi Mike,

    Thanks for the info. What kind of diode should I use specifically? As I'm new to building circuits, could you point me to a schematic or tutorial on how to connect the diodes properly?

    Thanks,
    Mark
  • Mike GreenMike Green Posts: 23,101
    edited 2008-07-20 02:23
    Go to the main Parallax web page and click on the Resources tab. You'll see a list with "Nuts and Volts Columns". Click on that and, on that page, look at column #6. This discusses the use of switching transistors to control things like relays. Any power diode like the 1N400x series will work. Also the 1N914 or equivalent will work.
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