Futurlec Solid State Relay

Bill Chennault

Mike and All--

Mike, thank you for suggesting the Futurlec SSR for use on my robot to allow a Stamp to control the 12vdc system. Although I have had the part for some time, I have been very busy doing other things and just yesterday mounted the solid state relay.

I have a very simple question. Since the SSR is triggered by an LED powered by the Stamp, should I place a 470 ohm resistor between the Stamp pin and the SSR?

I studied the data sheet (http://www.futurlec.com/Relays/SSRDC100V40A.shtml), but I am afraid I do not have enough experience yet to figure out the answer to my question.

Thanks!

--Bill

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Phil Pilgrim (PhiPi)

Since the input is rated for a voltage range, you can be sure there's a current-limiting resistor built-in. So you will not need an external one.

-Phil

Bill Chennault

Phil--

Ahh! So that may be a clue I can use in the future?

Just to be safe--and because I did not want to wait!--I stuck one in and it is allowing my BS2p40 to turn the SSR off and on according to my ohm meter. I believe I will leave the 470 ohm in for a bit and see what happens when I connect the HB25s.

With my extremely limited knowledge, I am under the impression that it cannot hurt. It might not work, but then I can just take it out without damage. Is this a good, conservative approach for the people such as myself?

Thanks!

--Bill

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You are what you write.

Phil Pilgrim (PhiPi)

Bill,

To make sure you get reliable operation with the 470-ohm resistor, measure the voltage across the SSR input terminals with it turned on. If it's above 3V, you should be okay. There's a chance, though, that it won't be, if the external resistor causes too much of a voltage drop.

-Phil

Bill Chennault

Phil--

With the 470 ohm resistor, the voltage measured across the SSR was 2.63vdc. I removed the 470 ohm resistor and the voltage rose to 4.42vdc which sounds better even to me!

Thank you, Phil.

Merry Christmas!

--Bill

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You are what you write.

Bill Chennault

Mike and All--

Mike, the Futurlec part is working perfectly in my application wherein I needed a Stamp to power on and off the 12 volt, 24 aH battery system. Currently that battery system powers the two track motors via two HB25s. This is an elegant way to bring up the HB25s, as well.

I want to leave the Stamps powered up all the time. But, there appears to be a current drain involving the HB25s--even when they are powered down--that kills my 7.2vdc Stamp battery system after a few days. The HB25 negative motor connection and VSS are tied together. And, of course, I have a pin from a Stamp tied to the HB25(s). That pin is left as an output when I power the 12vdc system down. I wonder if simply setting to input status after I power down the 12vdc system would cure the current drain problem?

Thanks for thinking about this.

--Bill

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You are what you write.

Mike Green

You can either set the pin to output low or to input. If you leave it set to output high, even pulsed high occasionally, the powered down HB25 acts as a short circuit when there's no power. Essentially the Stamp is trying to power the HB25's logic through its input protective diodes. If you set the I/O pin to input, do it after the HB25 is powered down and set it back to output low before you power up the HB25.

Bill Chennault

Mike--

Got'cha! It sounds like the best situation for me is to power the HB25s down, set the pin to input and then back to output low prior HB25 power up. With the Futurlec SSR in the loop, this will be easy.

· Thanks.

--Bill

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You are what you write.