Shop OBEX P1 Docs P2 Docs Learn Events
Nice Relays for $1.10 ea/Prop Potential — Parallax Forums

Nice Relays for $1.10 ea/Prop Potential

ercoerco Posts: 20,259
edited 2012-05-20 10:48 in General Discussion
http://www.ebay.com/itm/Lot-10-HASCO-713-5-High-Voltage-Reed-Relays-SIP-5V-Coil-2-5A-max-/260991831092?pt=LH_DefaultDomain_0&hash=item3cc4534c34

$11 for 10 SPST reed relays shipped, I bought one lot of 10, and I might get another. Only 2 lots left... Unusually high voltage rating. Unusually low coil current. 500 ohm coil (I measured 518 ohms), so less than 10 mA coil current at 5V operation, easily driven directly by a Stamp or other uC IO pin.

Guaranteed operation down to 3.75V, likely to work at Prop's 3.3 V. I can test at 3.3 V if anyone is interested.

Specs for 713-5 relay at http://www.hascorelays.com/reed_relays_700_series.asp

You better buy 'em before I do. :)

When dey gone, dey gone!

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-05-16 15:59
    erco, I'm interested in knowing if these will work with 3.3V.

    You can never have too many relays.
  • ercoerco Posts: 20,259
    edited 2012-05-16 16:35
    Duane Degn wrote: »
    erco, I'm interested in knowing if these will work with 3.3V. You can never have too many relays.

    Now you're barkin'. And don't miss out on these latching relays on sale for 79 cents. I tested them at 3.1V and they work great. I'm throwin' you gold, Duane! http://www.goldmine-elec-products.com/prodinfo.asp?number=G2011

    Will test the reed relays at 3-ishV tonite and report back. You can switch 120V 40W light bulbs with those. Don't dare me.
  • localrogerlocalroger Posts: 3,452
    edited 2012-05-16 16:55
    Erco, those latching relays are seriously tempting for the memory/register elements of a relay based CPU. I totally don't have time to do a project like that but the pull is ... must resist ... MUST RESIST
  • ercoerco Posts: 20,259
    edited 2012-05-16 17:14
    @localroger: I already have about 30 of them at home. I wanna get a BS1 banging 28 of them individually.

    But I may need significantly more for another project as you mentioned a relay-based CPU...

    At 79 cents, a hundred relays are just $79. What would YOU do with 100 latching relays? :)
  • localrogerlocalroger Posts: 3,452
    edited 2012-05-16 17:39
    Latching relays greatly simplify the relay-based CPU thing because they latch, making them memory elements. At 79c each they are actually *almost* cheap enough to use for main memory bits. In fact they're cheaper than main memory bits were in the early 1970's, when they were made of iron donuts (though those were a bit faster than the relays). The only relay CPU project I know of that didn't take this shortcut is The Tim-8: http://www.northdownfarm.co.uk/rory/tim/ He brilliantly used electrolytic capacitor dynamic RAM and roll tape (printed by a real computer unfortunately) for program memory. With latching relays this cheap you could almost make a computer as useful as the ones of the early 1960's without using other modern technology at all. I think that would be a worthwhile hack and if I wasn't so effing busy with other stuff I'd be seriously considering a major purchase here.
  • dmlandrumdmlandrum Posts: 13
    edited 2012-05-16 18:02
    erco wrote: »
    At 79 cents, a hundred relays are just $79. What would YOU do with 100 latching relays? :)

    You could make a simple electromechanical FPGA. :D
  • ercoerco Posts: 20,259
    edited 2012-05-16 19:18
    Good News #1: I bought another lot of 10 reed relays!

    Good News #2: There are 8 lots of ten left, not one!

    Good News #3: All ten of my relays worked at 3.2V (two AA batteries) so 3.3V Properation (I just coined that word, a penny anytime someone else uses it, like Parall-Axe) should be fine!
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2012-05-16 20:57
    Hi erco;

    This relay is a bit marginal running on a 3.3V Prop..

    Don't forget, the output FET has a resistance of about 140 ohms, (??), as I recall from a thread a while ago.

    So, let say the power supply is 5% low at about 3.1V. And the relay is 500 ohms.
    The resultant coil voltage would be about 2.4V. Clearly marginal.

    Sure, it may work but will it do it reliably. I'm concerned.

    I had a similar problem a number of years ago.
    I worked out a circuit that guaranteed my reed relays would switch with a marginal supply voltage.

    ReedRelayDriver.jpg


    Here's how it works. Lets start with the pin is low and the relay off.
    1. The capacitor charges to a voltage about midway between the guaranteed actuation voltage.
    2. The pin goes high which raises the voltage on the relay to about 3.3V + 2.1V = 5.4V and drifts back to 2.1V.
    3. The capacitor again charges to 2.1V.
    4. The pin goes low and the voltage goes down to 2.1V - 3.3V = -1.2 V and drifts back up to 2.1V.

    Note! The resister was chosen to set the "idle" relay current so the voltage is about the average of 3.75V & 0.5V, from the spec. You should do some testing to choose the correct value. Likewise for the non-polarized capacitor.

    There are restrictions to the usage. Don't change state until after waiting enough time for the capacitor to charge.

    Have fun.

    Duane J
    ReedRelayDriver.jpg
    394 x 312 - 24K
  • ercoerco Posts: 20,259
    edited 2012-05-17 04:49
    Neat workaround Duane J (another sharp Duane, wassup with that?), although not necessary in this case. Agreed, the 5V reed relay is operating on marginal voltage at 3.3V. But like the bumblebee who flies 'cuz it doesn't know it can't fly, the Prop drives this relay fine. Here I'm using P12 on a Boe, which I believe is a direct connection to the Prop. Kudos for making me use my PropBoe for the first time ever! :)
  • ercoerco Posts: 20,259
    edited 2012-05-19 14:14
    Just got my second batch of 10 and tested them on the Prop BoE, 100% function. I tested the voltage across the 500-ohm relay coil and got 3.13V @ 6.09 mA coil current, so the Prop's output FET resistance is more like 28 ohms in this application. 3.29 volts at Vdd and also 3.29V no-load voltage at the Prop pin driving the relay.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-05-19 15:59
    @Duane,

    You got erco to use a Prop. Amazing!

    Kudos to you.



    @erco,

    I still love the sound of a 'banging" relay.

    Duane
  • TtailspinTtailspin Posts: 1,326
    edited 2012-05-20 08:20
    erco, I gotta ask..
    So what do you think of the Prop now?
  • ercoerco Posts: 20,259
    edited 2012-05-20 10:48
    I think I have much to learn! :)
Sign In or Register to comment.